Papers Supporting a Skeptical-of-the-Consensus Position for 2014
248 total papers, 147 on natural contributions to climate change (sun, ocean oscillations, clouds)
Solar Influence on Climate (93 papers)
A comparison of the secular variation in the Northern Hemisphere temperature proxies with the corresponding variations in sunspot numbers and the fluxes of cosmogenic 10Be in Greenland ice shows that a probable cause of this variability is the modulation of temperature by the century-scale solar cycle of Gleissberg. This is consistent with the results obtained previously for Northern Fennoscandia (67-70 N, 19-33 E). Thus, evidence for a connection between century-long variations in solar activity and climate was obtained for the entire boreal zone of the Northern Hemisphere.
Global ocean temperature time series from the surface to depths of 2000 m since the year 2000 are found to agree in detail with those of other diverse climate indices. It is asserted that these systems are driven by a forcing unquestionably of solar origin that has two manifestations: (1) a direct phase-locked response to what is identified as a solar forcing at a frequency of 1.0 cycle/yr for the whole time series; (2) a second phase-locked response at a period of two years or three years. With these findings it is becoming clear that the entire climate system is responding to the varying incident solar radiation, and is subject to interactions, most likely nonlinear, that produce the subharmonics of two or three year period, and is moreover evolving non-continuously, as evidenced by breaks in the pattern whose timing can be identified with known climate shifts. The most prominent manifestations of the pattern are found in the El Niño/La Niña phenomena. As emphasized in , the “natural” periodicity of El Niño/La Niña is two or three years, and observations of longer intervals should be considered probable evidence for an intervening climate shift.
Global and hemispheric mean surface temperatures show a significant dependence on solar irradiance at λ [wavelengths] > 250 nm. Also, powerful volcanic eruptions in 1809, 1815, 1831 and 1835 significantly decreased global mean temperature by up to 0.5 K for 2–3 years after the eruption. Reduction of irradiance at λ [wavelengths] > 250 nm leads to a significant (up to 2%) decrease in the ocean heat content (OHC) between 0 and 300 m in depth, whereas the changes in irradiance at λ < 250 nm or in energetic particles have virtually no effect. Also, volcanic aerosol yields a very strong response, reducing the OHC of the upper ocean by up to 1.5%. In the simulation with all forcings, the OHC of the uppermost levels recovers after 8–15 years after volcanic eruption, while the solar signal and the different volcanic eruptions dominate the OHC changes in the deeper ocean and prevent its recovery during the DM. Finally, the simulations suggest that the volcanic eruptions during the DM had a significant impact on the precipitation patterns caused by a widening of the Hadley cell and a shift in the intertropical convergence zone.
The ratio changed from <1 to >1 after 1950, reflecting that the summer quarter rainfall of the study area became dominant under stronger influence of the Northwestern Pacific High. Eastern China temperatures varied with the solar activity, showing higher temperatures under stronger solar irradiation, which produced stronger summer monsoons. During Maunder, Dalton and 1900 sunspot minima, more severe drought events occurred, indicating a weakening of the summer monsoon when solar activity decreased on decadal timescales. On an interannual timescale, dry conditions in the study area prevailed under El Niño conditions, which is also supported by the spectrum analysis. Hence, our record illustrates the linkage of Asian summer monsoon precipitation to solar irradiation and ENSO: wetter conditions in the study area under stronger summer monsoon during warm periods, and vice versa. During cold periods, the Walker Circulation will shift toward the central Pacific under El Niño conditions, resulting in a further weakening of Asian summer monsoons.
Discussion: The persistent presence of these solar cycles and their connections with monsoon records over a wide range of regions highlight the dominated solar control of the monsoon at centennial timescales. The persistence of these different periodicities also indicates that the influence of the low-frequency solar activity on the AM [Asian Monsoon cycle] is independent of other climate backgrounds, such as ice volumes, orbital configurations, and concentrations of major greenhouse gases. The pronounced influence of the centennial-scale solar activities may, therefore, be amplified by some mechanism that has a global influence. The centennial-scale cycles have been suggested to be related to changes in the ocean component of the Earth’s climate system. The small solar variations could be amplified by ocean salinity changes in the North Atlantic, which then transmit the signals globally through the North Atlantic deep water formation and thermohaline circulation.
Physical mechanisms of solar forcing on the Earth’s climate involve: 1) direct heating of the Earth by the TSI, 2) solar ultraviolet radiation mechanism through stratosphere–troposphere interaction, and 3) galactic cosmic rays mechanism via feedbacks of cloud formation. Generally, an increase of cosmic ray flux could increase the global low cloud amount and therefore decrease atmospheric temperature and moisture, and the monsoon intensity. Alternatively, if the variation in cloud cover is greater at higher latitudes, the cloud influence on the AM is likely also associated with the ocean circulation, because the high sensitivity of the sea ice at high latitudes to the Earth’s radiation budget is influenced by the cloud cover. The link between cosmic rays, cloud and climate in East Asia is further supported by a tree-ring δ18O record in Japan during the Maunder Minimum, which shows that minima of decadal solar cycles correlate to increase in relative humidity in East Asia, rapid cooling in Greenland and decrease in Northern Hemisphere mean temperature.
Our analysis provides a first order validation of the ACRIM TSI composite approach and its 0.037 %/decade upward trend during solar cycles 21–22. The implications of increasing TSI during the global warming of the last two decades of the 20th century are that solar forcing of climate change may be a significantly larger factor than represented in the CMIP5 general circulation climate models.
Total solar irradiance is the primary energy source of the Earth’s climate system and therefore its variations can contribute to natural climate change. This variability is characterized by, among other manifestations, decadal and secular oscillations, which has led to several attempts to estimate future solar activity. Of particular interest now is the fact that the behavior of the solar cycle 23 minimum has shown an activity decline not previously seen in past cycles for which spatial observations exist: this could be signaling the start of a new grand solar minimum. We also found that the solar activity grand minima periodicity is of 120 years; this periodicity could possibly be one of the principal periodicities of the magnetic solar activity not so previously well recognized.
Solar influence on climate is now accepted as an important contribution to climate variability, particularly on regional scales. Reflecting this, the main focus has moved from TSI [total solar irradiance] towards understanding SSI [solar spectral irradiance] variations and their impact as well as shifting from the global responses to more regional responses. With better understanding of SSI [solar spectral irradiance], the importance of the top-down stratospheric UV mechanism has been widely accepted. Improved measurements of both TSI and SSI became available leading to more reliable solar cycle variation estimates, and a new value for the solar constant (TSI) was recommended for the IPCC AR5 climate simulations.
Late Holocene ecohydrological and carbon dynamics of a UK raised bog: impact of human activity and climate change
[S]olar forcing was a significant driver of climate change over the last ∼1000 years. Following the intensification of agriculture and industry over the last two centuries, the combined climatic and anthropogenic forcing effects become increasingly difficult to separate
Solar forcing of North Atlantic surface temperature and salinity over the past millennium
There were several centennial-scale fluctuations in the climate and oceanography of the North Atlantic region over the past 1,000 years, including a period of relative cooling from about AD 1450 to 1850 known as the Little Ice Age. These variations may be linked to changes in solar irradiance, amplified through feedbacks including the Atlantic meridional overturning circulation. Changes in the return limb of the Atlantic meridional overturning circulation are reflected in water properties at the base of the mixed layer south of Iceland. Here we reconstruct thermocline temperature and salinity in this region from AD 818 to 1780 using paired δ18O and Mg/Ca ratio measurements of foraminifer shells from a subdecadally resolved marine sediment core. The reconstructed centennial-scale variations in hydrography correlate with variability in total solar irradiance. We find a similar correlation in a simulation of climate over the past 1,000 years. We infer that the hydrographic changes probably reflect variability in the strength of the subpolar gyre associated with changes in atmospheric circulation. Specifically, in the simulation, low solar irradiance promotes the development of frequent and persistent atmospheric blocking events, in which a quasi-stationary high-pressure system in the eastern North Atlantic modifies the flow of the westerly winds. We conclude that this process could have contributed to the consecutive cold winters documented in Europe during the Little Ice Age.
Causes of the heating and qualitative estimates of contributions of different factors in the global climate change remain unclear in many aspects. In still more degree, this refers to climate forecasts with accounting for anthropogenic impacts. There are many ambiguities in recent ideas about the global climate and causes of its variations. Observable correlations between long-term variations in the global temperature (GT) and CO2 content do not mean that the CO2 increase causes an increase in the global temperature. Actually observable temperature rise in the ocean also results in the increased content of CO2 in the atmosphere; therefore, such changes can be a consequence, but not a cause of global heating. In the opinion of adherents of the anthropogenic nature of global heating in the 20th century, the most significant evidence is the rate of the surface air temperature increase, which is unprecedentedly high (0.7°/100 years) and was not observed earlier. However, recent investigations of ancient ices, sampled during the boring of Greenland and Antarctica ice surfaces, allowed getting information on events of global heating and cooling off on different time scales. Based on oxygen-isotopic analysis of the ice in the Greenland core Summit, data on temperature variations in high latitudes of the North Hemisphere for the last 250 [thousand years] were found. Analysis of temporal variations in the air temperature in the past has shown that the rate of air temperature variation in high latitudes was not only comparable with that in the 20th century, but significantly exceeded it. The change from very cold climatic conditions to warm ones was very fast (practically, instant from the geological point of view), i.e., during several tens of years.
The study of the solar activity effect on the weather and climate has a long history. The comparison of characteristics of climate and solar activity on big time scales shows a great similarity in their behavior. [T]he variable part of the energy flow, incident on the upper boundary of the atmosphere and related to the solar activity, cannot directly change the energy of the Earth climatic system. Calculations in the framework of global climate models also show that variations in the solar constant cannot contribute significantly to variations in the global temperature. At the same time, in the framework of empiric models, the estimate of the solar activity contribution in the variation in the air global temperature in the 20th century is about 70%
We report on the existence and nature of Holocene solar and climatic variations on centennial to millennial timescales. We introduce a new solar activity proxy, based on nitrate (NO3−) concentration from the Talos Dome ice core, East Antarctica. We also use a new algorithm for computing multiple-cross wavelet spectra in time–frequency space that is generalized for multiple time series (beyond two). Our results provide a new interpretive framework for relating Holocene solar activity variations on centennial to millennial timescales to co-varying climate proxies drawn from a widespread area around the globe. Climatic proxies used represent variation in the North Atlantic Ocean, Western Pacific Warm Pool, Southern Ocean and the East Asian monsoon regions. Our wavelet analysis identifies fundamental solar modes at 2300-yr (Hallstattzeit), 1000-yr (Eddy), and 500-yr (unnamed) periodicities, leaves open the possibility that the 1500–1800-yr cycle may either be fundamental or derived, and identifies intermediary derived cycles at 700-yr and 300-yr that may mark rectified responses of the Atlantic thermohaline circulation to external solar modulation and pacing. … It is obviously premature to reject possible links between changing solar activity at these multiple scales and the variations that are commonly observed in paleoclimatic records.
We find that the variations of SSN [sunspot number] and T [temperature] have some common periodicities, such as the 208 year (yr), 521 yr, and ~1000 yr cycles. The correlations between SSN and T are strong for some intermittent periodicities. However, the wavelet analysis demonstrates that the relative phase relations between them usually do not hold stable except for the millennium-cycle component. The millennial variation of SSN [sunspot number] leads that of T by 30–40 years, and the anti-phase relation between them keeps stable nearly over the whole 11,000 years of the past. As a contrast, the correlations between CO2 and T are neither strong nor stable. These results indicate that solar activity might have potential influences on the long-term change of Vostok’s local climate during the past 11,000 years before modern industry.
Radiative forcing in both the short and long-wave lengths reaching the Earth’s surface accounted for more than 80% of the inter-annual variations in the mean yearly temperatures measured at Potsdam, Germany during the last 120 years [1893-2012]. Three-quarters of the increase in the long-wave flux was due to changes in the water content of the lower atmosphere; the remainder [25%] was attributed to increases in CO2 and other anthropogenic, radiatively active gases. Over the period radiative forcing in the short-wave flux [solar forcing] slightly exceeded [0.76 W/m2 per decade] that in the long wave [0.64 W/m2 per decade total, 0.16 W/m2 per decade for CO2].
Marine microorganisms adapt to their habitat by structural modification of their membrane lipids. This concept is the basis of numerous molecular proxies used for paleoenvironmental reconstruction. Archaeal tetraether lipids from ubiquitous marine planktonic archaea are particularly abundant, well preserved in the sedimentary record and used in several molecular proxies. Temporal variations of this lipid ratio indicate a strong influence of the ∼200-y de Vries solar cycle on reconstructed sea surface temperatures with possible amplitudes of several degrees and suggest signal amplification by a complex interplay of ecological and environmental factors. Laser-based biomarker analysis of geological samples has the potential to revolutionize molecular stratigraphic studies of paleoenvironments.
The so-called ‘Little Ice Age’ (LIA) of the 15th to 19th centuries AD is well-attested from much of Europe and from some other parts of the Northern Hemisphere. It has been attributed to solar forcing, associated with reduced solar activity, notably during the Spörer, Maunder and Dalton solar minima, although other causes have also been proposed and feature strongly in recent papers. Detection of the LIA in some proxy-climate records from the Southern Hemisphere is less clear, leading to suggestions that the LIA was perhaps not a global phenomenon. Resolving this issue requires more data from the Southern Hemisphere. We present proxy-climate data (plant macrofossils; peat humification) covering the past three millennia from an ombrotrophic mire (peat bog) in Tierra del Fuego, southern South America, but focus our discussion on the period traditionally associated with the LIA. During parts of this time, the mire surface was apparently relatively dry compared with much of its 3000-year record. It was reported earlier that a particularly dry episode in the mire coincided with the 2800 cal. BP ‘solar’ event (since identified as a Grand Solar Minimum), which was attributed to solar-driven changes in atmospheric circulation, and more specifically to a shift in position of the Westerlies. Parts of the LIA record show a similar shift to dryness, and we invoke a similar cause. The shifts to and from dry episodes are abrupt. These new data support the concept of a global LIA, and for at least the intense dry episodes might reinforce the claim for solar forcing of parts of the LIA climate.
[A] marked negative peak in solar irradiance at 2700 cal yrs BP seems to have provoked cooling on the continents and a southward shift of the ITCZ associated with a probable reduction in the Atlantic Meridian Overturning Circulation.
The Pacific North American (PNA) teleconnection has a strong influence on North American climate. Instrumental records and century-scale reconstructions indicate an accelerating tendency towards the positive PNA state since the mid-1850s, but much less is known about long-term PNA variability. Here we reconstruct PNA-like climate variability during the mid- and late Holocene using paired oxygen isotope records from two regions in North America with robust, anticorrelated isotopic response to the modern PNA. We identify mean states of more negative and positive PNA-like climate during the mid- and late Holocene, respectively. Superimposed on the secular change between states is a robust, quasi-200-year oscillation, which we associate with the de Vries solar cycle.
Centennial-scale North American climate variability during the Holocene has previously been linked to variations in solar radiation. The 195- and 219-year periodicities identified and associated with modulation of palaeo-PNA variability here are similar to that of the 210-year de Vries (Suess) solar cycle, which may suggest a persistent link between PNA-associated North American climate changes and solar variability during the MH and LH [Mid and Late Holocene]. Previous studies have demonstrated that variation in solar ultraviolet radiation can lead to shifts in regional atmospheric circulation patterns and the polar jet through heating and ozone chemistry in the middle atmosphere. North American circulation patterns for low and high solar activity winters during the period of instrumental record show strong associations with PNA+ and PNA− circulation patterns, respectively. A recent 275-year PNA reconstruction further supports this association, with two prominent solar minima (Dalton and Damon) being characterized by strong PNA+ conditions.
Abstract: Climate records of the mid-to-late Holocene transition, between 3–4 thousand years before present (ka), often exhibit a rapid change in response to the gradual change in orbital insolation. Here we investigate North Atlantic Central Water circulation as a possible mechanism regulating the latitudinal temperature gradient (LTG), which, in turn, amplifies climate sensitivity to small changes in solar irradiance.
Introduction: Observations over the past century indicate that changes in the North Atlantic Oscillation (NAO), exert the dominant control on the path and strength of the mid-latitude Westerlies and climate in the North Atlantic on interannual to decadal timescales (Hurrell, 1995; Visbeck et al., 2003). The region with the strongest response to NAO-modulated wind-stress is the northeastern subpolar basin of the Atlantic Ocean, where the strength of the Icelandic Low enhances westerly air flow by up to 8 m s−1 (Hurrell, 1995) and thereby lowers sea surface temperatures (SST) by several tenths of degrees (∼0.7 ◦C) during extremely positive NAO (+) years (Furevik and Nilsen, 2005; Johnson and Gruber, 2007). Subpolar Mode Water (SPMW) which forms in this region during winter convection (Tomczak and Godfrey, 1994) is thus highly susceptible to NAO phase shifts. … On centennial timescales, there is evidence (Ammann et al., 2007; Knudsen et al., 2009; Lockwood et al., 2010; Lohmann et al., 2004; Swingedouw et al., 2010) for the existence of similar ocean-atmosphere linkages that communicate and amplify relatively small changes in total solar irradiance (#TSI) into a climate signal extending beyond the northeastern Atlantic region (Lean, 2010; Morley et al., 2011; Shindell et al., 2001).
Results: ENACW [Eastern North Atlantic Central Waters] cooling of 1.2°C from ∼9.6°C to ∼8.6°C between 3.3 and 2.6 ka [thousand years ago] followed by distinct century scale cooling events centered at, 1.3, 0.8 and 0.4 ka. These events correspond to the commonly referenced Dark Ages Cold Period (DACP), Wolf solar minima (end of Viking colonization in Greenland), and the Maunder and Spörer solar minima or the Little Ice Age (LIA) (Fig. 2, Fig. A1). Warm intervals correspond to a plateau between 2.1 and 1.7 ka the so called Roman Warm Period (RWP), and centennial warm peaks centered during solar maxima at 1.1 (Medieval Warm Period), 0.6 and 0.2 ka
[W]e can conclude that there has been an emergence of causality running from sunspot numbers to global temperatures only recently at cycle length of 10.3 months and above.
Climate and ocean circulation in the North Atlantic region was mainly influenced over the course of the Holocene by two driving factors: disintegrating ice sheets, and the seasonally varying, orbitally-induced insolation [surface solar radiation] trends. During the early Holocene, the Laurentide ice sheet released large melt water fluxes into the North Atlantic affecting ocean circulation and in combination with the cooling effect of the remnant ice sheet, cooling large parts of the Northern Hemisphere. This impact is accompanied in the Nordic Seas by a rather small, but significant, amount of Greenland ice sheet melting that accompanied these cooling effects even further.
The influence of variations in solar activity on earth’s surface temperature is a key question in climate-change attribution. On the basis of natural cyclic sea surface temperatures and the annual mean daily sunspot number as a proxy for variability in solar influence on the energy retained by the planet, a predictive equation derived from well-understood physical principles proves capable of reproducing observed anomalies in annual global mean surface temperature since before 1900 with 90% accuracy (R2 = 0.9049). This accuracy results even where a zero-contribution from changes in greenhouse-gas concentrations is assumed. Here we show that the cumulative influence of the unusually elevated solar activity in the 64 years 1941-2005, as calculated using the time-integral of sunspot number anomalies (with a proxy factor) might have been a primary cause of the global warming observed through 2001. After 2001 the low solar activity is consistent with the observed flat average global temperature trend. The physically-based predictive equation, with the widely-projected decline in solar activity, moderated by the substantial effective thermal capacitance of the planet, especially the oceans, projects a downtrend steeper than 0.1K/decade.
[A] Holocene record of sun activity (sunspots) was utilized to evaluate long-term solar forcing. The results indicated that the UV-absorbance of cladoceran remains was highest (i.e. maximum UV-induced pigmentation) for a short period during the early Holocene and for several millennia during the mid-Holocene [when global temperatures were warmer than present]. Sun activity was high during these time intervals
The Mount Logan ALow [a low pressure center controlling atmospheric circulation in the Northern Hemisphere] proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various time scales, with stronger solar irradiance generally associated with a weaker ALow and La Niña-like tropical conditions
On the centennial timescale, the quasi-periodicities around 88 and 210 years suggest a strong link between solar activity and monsoon rainfall. The millennial monsoon cycle in northeastern China is associated with sea surface temperature (SST) variations in two active centers of the summer monsoon, the western Pacific Subtropical High (WPSH) and the Okhotsk High.
The mid- to late Holocene interval is characterised by a highly variable climate in response to a gradual change in orbital insolation. … The dates of major climate, volcanic, and archaeological event(s) determined using our model are in good agreement with the independently determined ages of the same events from other archives, confirming the accuracy of our age model; (3) test the sensitivity of the seasonal proxies to the available data on mid-Holocene changes in temperature and precipitation; (4) demonstrate that the changes in lake eutrophicity are correlative with temperature changes in NW Europe and probably triggered by solar variability; and (5) show that the early Iron Age onset of eutrophication in Lake Holzmaar was climate induced and began several decades before the impact of anthropogenic activity was seen in the form of intensified detrital erosion in the catchment area. Our work has implications for understanding the impact of climate change and anthropogenic activities on limnological systems.
The results of this comprehensive analyses suggest that the AHP [African Humid Period] highstand in the Suguta Valley was the direct consequence of a northeastwards shift in the Congo Air Boundary (CAB), which was in turn caused by an enhanced atmospheric pressure gradient between East Africa and India during a northern hemisphere insolation [solar radiation] maximum. Rapidly decreasing water levels of up to 90 m over less than a hundred years are best explained by changes in solar irradiation either reducing the East African-Indian atmospheric pressure P gradient and preventing the CAB from reaching the study area, or reducing the overall humidity in the atmosphere, or a combination of both these effects.
It is found that both the QBO [Quasi-biennial oscillation] and solar forcings in low latitudes can perturb the late winter polar vortex, likely via planetary wave divergence, causing an early breakdown of the vortex in the form of sudden stratospheric warming.
Furthermore, the climate changes across the North Pacific co-vary over widespread regions, such as the eastern tropical Pacific and the northern Red Sea, and the reconstructed solar activity. The cross-spectral and wavelet analyses show that the East Asian winter monsoon shares some cyclicity with the solar variability. Our results suggest that the solar activity is a fundamental forcing producing the centennial-scale EAWM [East Asian winter monsoon] variability mediated by the large-scale climate linkages.
It appears that the natural variability of climate change in NC during 1950–2009 can be explained mostly by AMO and solar activity.
Continuous, high-resolution paleoclimate records from the North Pacific region spanning the past 1500 years are rare; and the behavior of the Aleutian Low (ALow) pressure center, the dominant climatological feature in the Gulf of Alaska, remains poorly constrained. The Mount Logan ALow [Alelutian Low] proxy record shows strong similarities with tropical paleoclimate proxy records sensitive to the El Niño–Southern Oscillation and is consistent with the hypothesis that the Medieval Climate Anomaly was characterized by more persistent La Niña-like conditions while the Little Ice Age was characterized by at least two intervals of more persistent El Niño-like conditions. The Mount Logan ALow proxy record is significantly (p < 0.05) correlated and coherent with solar irradiance proxy records over various time scales, with stronger solar irradiance generally associated with a weaker ALow and La Niña-like tropical conditions.
Conclusion: The sudden break-up of the ice cover and the concentrated release of high amounts of sea ice and icebergs trapped therein at 17.6 ka BP then could have acted as a trigger for the AMOC break-down during Heinrich Event 1. Similarly, an almost perennial sea ice cover in Fram Strait coincided with a weakened AMOC during the Younger Dryas. The latter expansion of sea ice likely resulted from the overall increase in sea ice formation in the Arctic Ocean due to a significant deglacial freshwater release and sea level rise. The high insolation and a probably strengthened or reorganised oceanic and atmospheric circulation within the Arctic Ocean promoted the export of sea ice through Fram Strait to the North Atlantic where it impacted on thermohaline processes and contributed to the Younger Dryas AMOC weakening. Highest phytoplankton and lowest ice algae productivity characterised the early Holocene when a maximum insolation [surface solar radiation] led to a significant sea surface warming and sea ice retreat in the study area.
Highlights: •We reconstruct late Holocene climate history of subtropical west Guandong in South China. •Multi-proxy records reveal three stronger and three weaker Asian summer monsoon periods. •Three dry and cold intervals may correlate with the Bond events 3, 2, and 1. •The trend of climatic changes and the significant cycles reflect strong signals of solar forcing. •Solar output and oceanic–atmospheric circulation played a role in the late Holocene climate.
The surface response to 11 year solar cycle variations is investigated by analyzing the long-term mean sea level pressure and sea surface temperature observations for the period 1870–2010. The analysis reveals a statistically significant 11 year solar signal over Europe, and the North Atlantic provided that the data are lagged by a few years. The delayed signal resembles the positive phase of the North Atlantic Oscillation (NAO) following a solar maximum. The corresponding sea surface temperature response is consistent with this. A similar analysis is performed on long-term climate simulations from a coupled ocean-atmosphere version of the Hadley Centre model that has an extended upper lid so that influences of solar variability via the stratosphere are well resolved.
Appropriate solar proxy models demonstrate the existence of a significant sun-climate relation.
[T]he solar signature in the surface temperature record can be recognized only using specific techniques of analysis that take into account non-linearity and filtering of the multiple climate change contributions; the post 1880-year temperature warming trend cannot be compared or studied against the sunspot record and its 11-year cycle, but requires solar proxy models showing short and long scale oscillations plus the contribution of anthropogenic forcings, as done in the literature. Multiple evidences suggest that global temperatures and sunspot numbers are quite related to each other at multiple time scales. Thus, they are characterized by cyclical fractional models. However, solar and climatic indexes are related to each other through complex and non-linear processes.
The present study points at a potentially large impact of the increased SW [short wave solar radiation] forcing during EHIM [Early Holocene, 9,000 to 6,000 years ago] through the surface albedo feedback, leading to a breakdown of the perennial sea ice cover into a state dominated by ice free summers. Above we have discussed some mechanisms and feedback processes that are not included in the present model study. Although some of the in this model omitted mechanisms are believed to be important (e.g. the surface albedo feedback associated with vegetation) the current understanding of the climate system as a whole is far from complete. Evidence of problems with the coupled GCMs [general circulation models] can be found in the PMIP [models of paleoclimate] literature. For instance Jiang et al. (2012) show that 35 out of 36 PMIP models produce colder than present day climate in China during mid-Holocene which is in stark contrast to available multiproxy data for the same time and region indicating 1–5 °C warmer than present day conditions. Suffice to say that further research on the coupled global climate system is needed before any conclusive results regarding the evolution of the Arctic sea ice cover during Holocene can be reached through climate modelling. …. Several studies suggest that the GHG concentrations were lower during the [Early Holocene Insolation Maximum, ∼ 9,000 years ago] (Indermuhle, 1999, Brook et al., 2000 and Sowers et al., 2003). However, when running the model with GHG [greenhouse gas] concentrations estimated from paleo-proxy data (LeGrande and Schmidt, 2009) for 9000 years BP [before present] yields only a moderate effect on the ice cover thickness of typically ∼0.1 m. This is consistent with the results of CAPE Project members (2001) showing also only marginal effects of the GHG [greenhouse gas] concentration variations on the Arctic climate.
Nile discharge was highly variable on multicentennial time scale during the early to middle Holocene, being strongly influenced by variable solar activity. This solar-driven variability is also recorded in contemporaneous SIM records…Solar-driven variability in Nile discharge also influenced paleoenvironmental conditions in the eastern Mediterranean.
There is strong statistical evidence that solar activity influences the Indian summer monsoon rainfall. To search for a physical link between the two, we consider the coupled cloud hydrodynamic equations, and derive an equation for the rate of precipitation that is similar to the equation of a forced harmonic oscillator, with cloud and rain water mixing ratios as forcing variables. We also solved the precipitation equation by allowing for the effects of long-term variation of aerosols. We tentatively conclude that the net effects of aerosols variation are small, when compared to the solar factors, in terms of explaining the observed rainfall variability covering the full Indian monsoonal geographical domains.
This study provides evidence of the robust response of the East Asian monsoon rainband to the 11-yr solar cycle and first identify the exact time period within the summer half-year (1958–2012) with the strongest correlation between the mean latitude of the rainband (MLRB) over China and the sunspot number (SSN). This period just corresponds to the climatological-mean East Asian mei-yu season, characterized by a large-scale quasi-zonal monsoon rainband (i.e., 22 May–13 July). Both the statistically significant correlation and the temporal coincidence indicate a robust response of the mei-yu rainband to solar variability during the last five solar cycles. During the high SSN years, the mei-yu MLRB lies 1.2° farther north, and the amplitude of its interannual variations increases when compared with low SSN years. The robust response of monsoon rainband to solar forcing is related to an anomalous general atmospheric pattern with an up–down seesaw and a north–south seesaw over East Asia.
Our records show that the regional temperatures during the MWP exceeded those in the recent warm period. [W]e estimated that lake temperatures were higher by ~4.0°C, ~1.9°C and ~0.5°C for Lake Sugan, Gahai and Qinghai respectively during the MWP optimum. Further, our temperature reconstructions, within age uncertainty, can be well correlated with solar irradiance changes, suggesting a possible link between solar forcing and natural climate variability, at least on the northern Tibetan Plateau.
[T]he modern Grand maximum (which occurred during solar cycles 19–23, i.e., 1950–2009) was a rare or even unique event, in both magnitude and duration, in the past three millennia. Except for these extreme cases, our reconstruction otherwise reveals that solar activity is well confined within a relatively narrow range.
This research examines a 17-year database of UV-A (320–400 nm) and visible (400–600 nm) solar irradiance obtained by a scanning spectroradiometer located at the South Pole. The goal is to define the variability in solar irradiance reaching the polar surface… To eliminate changes associated with the varying solar elevation, the analysis focuses on data averaged over 30–35 day periods centered on each year’s austral summer solstice. The long-term average effect of South Polar clouds is a small attenuation, with the mean measured irradiances being about 5–6% less than the clear-sky values, although at any specific time clouds may reduce or enhance the signal that reaches the sensor. The instantaneous fractional attenuation or enhancement is wavelength dependent, where the percent deviation from the clear-sky irradiance at 400–600 nm is typically 2.5 times that at 320–340 nm. When averaged over the period near each year’s summer solstice, as measured by the 10.7 cm solar radio flux. An approximate 1.8 ± 1.0% decrease in ground-level irradiance occurs from solar maximum to solar minimum for the wavelength band 320–400 nm. The corresponding decrease for 400–600 nm is 2.4 ± 1.9%. The best-estimate declines appear too large to originate in the sun. If the correlations have a geophysical origin, they suggest a small variation in atmospheric attenuation [clouds] with the solar cycle over the period of observation, with the greatest attenuation [more clouds] occurring at solar minimum.
We show that during the solar cycle minima around 1879 and 1901 the average solar wind speed was exceptionally low, implying the Earth remained within the streamer belt of slow solar wind flow for extended periods. This is consistent with a broader streamer belt, which was also a feature of the recent low minimum (2009), and yields a prediction that the low near-Earth IMF during the Maunder minimum (1640-1700), as derived from models and deduced from cosmogenic isotopes, was accompanied by a persistent and relatively constant solar wind of speed roughly half the average for the modern era.
When the Pacific Decadal Oscillation is in phase with the 11 year sunspot cycle, there are positive sea level pressure (SLP) anomalies in the Gulf of Alaska, nearly no anomalous zonal SLP gradient across the equatorial Pacific, and a mix of small positive and negative sea surface temperature (SST) anomalies there. When the two indices are out of phase, positive SLP anomalies extend farther south in the Gulf of Alaska and west into eastern Russia, with a strengthened anomalous zonal equatorial Pacific SLP gradient and larger magnitude and more extensive negative SST anomalies along the equatorial Pacific. In the North Atlantic, when the North Atlantic Oscillation (NAO) is in phase with the sunspot peaks, there is an intensified positive NAO SLP pattern. When the NAO is out of phase with the peaks, there is the opposite pattern (negative NAO). The relationships are physically consistent with previously identified processes and mechanisms and point the way to further research.
We conclude that variations in solar activity play a significant role in monsoonal rainfall variability at multi-decadal and longer timescales. The combined effect of orbital and solar forcing explains important details in the temporal evolution of AISM rainfall during the last 6000 years.
Our analyses show that the combined solar and volcanic forcing is highly correlated to both existing AMO reconstructions over the past two centuries. The correlation between the AMO reconstructions and the combined external forcing record is highly significant for both the tree-ring and multiproxy records after AD 1775 when compared with 10,000 randomly generated red-noise AR1 data. Comparison with red-noise AR1 time series suggests that the abrupt change in correlation around AD 1775 observed for the tree-ring AMO is highly unlikely to occur by chance (P~0.005). Cross-correlation analyses furthermore show that both AMO reconstructions temporally lag the combined solar and volcanic forcing by ~5 years in the interval following the transition around AD 1775. . In these model simulations, the AMO lags the external forcing by ~5 years, which is in close agreement with the ~5-year lag observed in the present study for the period after AD 1775. A more detailed explanation for this lagged North Atlantic SST response to solar variability was recently proposed based on idealized experiments showing that a step change in ultraviolet forcing has an immediate impact on the atmosphere, which subsequently takes several years to accumulate in the ocean. During this time, the atmospheric response continues to increase, suggesting a positive feedback between the ocean and atmosphere. Similarly, several studies indicate that the ‘top-down’ stratosphere–troposphere mechanism represents an important response to solar variability, particularly at high latitudes.
The now arid Great Basin of western North America hosted expansive late Quaternary pluvial lakes, yet the climate forcings that sustained large ice age hydrologic variations remain controversial. Here we present a 175,000 year oxygen isotope record from precisely-dated speleothems that documents a previously unrecognized and highly sensitive link between Great Basin climate and orbital forcing. Our data match the phasing and amplitudes of 65°N summer insolation [surface solar radiation], including the classic saw-tooth pattern of global ice volume and on-time terminations.
Discussion: Our data document a previously unrecognized and robust link between Great Basin climate and summer insolation [surface solar radiation]. The saw-tooth character of the δ18O-GB record over the past 175 ka suggests that global ice volume and insolation are first-order controls on western North America paleoclimate.
Changes in solar activity have previously been proposed to cause decadal- to millennial-scale fluctuations in both the modern and Holocene climates. Direct observational records of solar activity, such as sunspot numbers, exist for only the past few hundred years, so solar variability for earlier periods is typically reconstructed from measurements of cosmogenic radionuclides such as10Be and 14C from ice cores and tree rings. We conclude that the mechanism behind solar forcing of regional climate change may have been similar under both modern and Last Glacial Maximum climate conditions.
Wanner’s paper reminds us that insolation [surface solar radiation ] rose from the end of the Last Glacial Maximum into the early Holocene, reaching a peak roughly 10000 years ago, and that the Holocene of the Northern Hemisphere warmed gradually from its beginning at 11700 years ago to the mid-Holocene Thermal Maximum (or Climate Optimum) between 10000 and 7000 years ago. … As Wanner et al. (2014) made plain, superimposed on this insolation-driven pattern are other forcing factors for climate, among them variations in the Sun’s output, in volcanic activity, and in the supply of greenhouse gases, most notably CO2 and CH4. Early in the Holocene, outbreaks of freshwater from glacial lakes in North America led to local cooling of the Northern Hemisphere, especially 8200 years ago in an event that has a global signature. Late Holocene cold events of the past 3000 years seem largely to represent the superimposition upon the orbital decline in insolation of large tropical volcanic eruptions and Grand Solar Minima, such as the Maunder Minimum, a period of zero sunspots between AD 1645 and 1715 at the heart of the Little Ice Age. Other internal climate system processes must have also been at work. Small changes in CO2 and CH4 throughout the Holocene do not seem to have had a significant effect on global temperature until their sharp exponential rise beginning post-1800.
We investigate the role of the 11-year solar cycle in modulating the Pacific-North American (PNA) influence on North American winter climate. The PNA appears to play an important conduit between solar forcing and surface climate. The low solar (LS) activity may induce an atmospheric circulation pattern that resembles the positive phase of the PNA, resulting in a significant warming over northwestern North America and significant dry conditions in the Pacific Northwest, Canadian Prairies and the Ohio-Tennessee-lower Mississippi River Valley. The solar-induced changes in surface climate share more than 67% and 14% of spatial variances in the PNA-induced temperature and precipitation changes for 1950-2010 and 1901-2010 periods, respectively. These distinct solar signatures in North American climate may contribute to deconvolving modern and past continental-scale climate changes and improve our ability to interpret paleoclimate records in the region.
Within the context of an overall strong EASM [East Asian Summer Monsoon] during the MCA [Medieval Climate Anomaly], a weakening of the monsoon was detected in many of the records during the period 1000–.\1100 A.D. Comparison of the timing of this event with variations of sea surface temperature (SST) of the Indian Ocean-western Pacific and with proxy records of solar activity reveals a significant covariation, suggesting that the driver of the event may have resulted from changes in the Indian Ocean-western Pacific, related to changes in solar activity.
[E]ffective moisture history was: hyper-arid at 12.8–11.6 ka [thousand years ago], humid and variable at 11.6–8.3 ka, moderately humid and stable at 8.3–3.5 ka, and increasingly arid at 3.5–0 ka; (3) the effective moisture change was mainly controlled by the Asian summer monsoon (ASM), which mainly followed the change of Northern Hemispheric summer insolation [surface solar radiation], and the westerlies strengthened and increased the aridity in the QB when the ASM shrank.
Abrupt climate changes did not only happen during glacials but also during interglacials such as the Holocene. Marine sediments provide evidence for the periodic occurrence of centennial-scale events with enhanced iceberg discharge during the past 11.000 years (Bond et al., 2001). These events were chronologically linked to reduced solar activity as reconstructed using cosmogenic isotopes (Bond et al., 2001), indicating that even an external forcing that is considered to be small, has a potential impact on climate due to several feedback mechanisms (Renssen et al., 2006).
When the Pacific Decadal Oscillation is in phase with the 11 year sunspot cycle, there are positive sea level pressure (SLP) anomalies in the Gulf of Alaska, nearly no anomalous zonal SLP gradient across the equatorial Pacific, and a mix of small positive and negative sea surface temperature (SST) anomalies there. When the two indices are out of phase, positive SLP anomalies extend farther south in the Gulf of Alaska and west into eastern Russia, with a strengthened anomalous zonal equatorial Pacific SLP gradient and larger magnitude and more extensive negative SST anomalies along the equatorial Pacific. In the North Atlantic, when the North Atlantic Oscillation (NAO) is in phase with the sunspot peaks, there is an intensified positive NAO SLP pattern. When the NAO is out of phase with the peaks, there is the opposite pattern (negative NAO). The relationships are physically consistent with previously identified processes and mechanisms and point the way to further research.
This study quantitatively diagnoses the linkage between Total Solar Irradiance (TSI) and Earth’s near-surface air temperature (TAS) of past 1000-year as simulated by Paleoclimate Modeling Intercomparison Project 3 (PMIP3) models. The results demonstrate that there is causal feedback of TAS [near-surface air temperatures] from TSI variations, especially in the tropical and subtropical regions. The consistency between models in simulating solar signal in TAS responses is significant in these regions with more than 70% selected models showing agreement. There is no agreement between models in simulating TSI-TAS relationship in mid and high latitude regions.
The sun-hurricane connection: Diagnosing the solar impacts on hurricane frequency…..
Abstract: Regional hurricane frequency over the period 1866–2010 is examined in response to September sunspot number (SSN) while controlling for other relevant climate factors. The response features a 13 % reduction in probability of annual hurricane occurrence for southeastern Cuba, the southern Bahama islands, Haiti, and Jamaica when the SSN is 80 sunspots. In contrast, hurricane risk in regions of the southeastern Atlantic is predicted to increase by 73 % when the SSN is 160 sunspots. … Variations in solar activity are monitored by sunspots. Sunspots are visible disturbances on the photosphere of the sun. During the sun’s 11-year (on average) geographic switching of magnetic poles, dark central cores (umbra) appear in various shapes (penumbra) in response to the convective inhibition of solar plasma induced by migrating magnetic fields (Weiss, 2007). The cooler, darker sunspots decrease overall solar luminosity. However, cloud-like features (faculae) above the sunspot are roughly 300 K higher than the normal surface temperature of the sun of 5,778 K, an increase of 5.2%. The result is higher overall solar irradiance, especially in the ultraviolet and extreme ultraviolet wavelengths as described by Planck’s law. Earth’s stratospheric ozone absorbs this additional UV energy, and the result is increased stratospheric and upper-tropospheric temperatures (Labitzke et al., 2002, Hood, 2003).
Insolation [solar radiation] and glacial-interglacial control on southwestern African hydroclimate over the past 140,000 years
Southwestern Africa was wetter during southern hemisphere summer insolation [solar radiation] maxima.
An interhemispheric hydrologic seesaw—in which latitudinal migrations of the Intertropical Convergence Zone (ITCZ) produce simultaneous wetting (increased precipitation) in one hemisphere and drying in the other—has been discovered in some tropical and subtropical regions. For instance, Chinese and Brazilian subtropical speleothem (cave formations such as stalactites and stalagmites) records show opposite trends in time series of oxygen isotopes (a proxy for precipitation variability) at millennial to orbital timescales, suggesting that hydrologic cycles were antiphased in the northerly versus southerly subtropics. This tropical to subtropical hydrologic phenomenon is likely to be an initial and important climatic response to orbital [solar] forcing. The impacts of such an interhemispheric hydrologic seesaw on higher-latitude regions and the global climate system, however, are unknown. Here we show that the antiphasing seen in the tropical records is also present in both hemispheres of the mid-latitude western Pacific Ocean. Furthermore, our result implies that insolation [solar radiation]-driven ITCZ dynamics may provoke water vapour and vegetation feedbacks in northern mid-latitude regions and could have regulated global climate conditions throughout the late Quaternary ice age cycles.
above a certain threshold and 2) is affected by the consumption of incoming radiation during snowmelt.
Interestingly, the underlying periodicity in groundwater recharge fluctuations is similar to those of solar-induced climate cycle “Suess wiggles” and appears to be coherent with phases of the climate fluctuations and solar cycles. Matching periodicity of groundwater recharge rates and solar and climate cycles renders a strong impression that solar-induced climate signals may act as a critical amplifier for driving the underlying hydrographic cycle through the common coupling of long-term Sun-climate groundwater linkages.
We use Indian temperature data of more than 100 years [1901–2007] to study the influence of solar activity on climate. We study the Sun–climate relationship by averaging solar and climate data at various time scales; decadal, solar activity and solar magnetic cycles. We also consider the minimum and maximum values of sunspot number (SSN) during each solar cycle. This parameter SSN is correlated better with Indian temperature when these data are averaged over solar magnetic polarity epochs (SSN maximum to maximum). Our results indicate that the solar variability may still be contributing to ongoing climate change and suggest for more investigations.
Relatively warm conditions with a strong influence of the Irminger Current (IC) were indicated for the early part of the record (~ 5000–3860 cal. yr BP), corresponding in time to the latest part of the Holocene Thermal Maximum. Between 3860 and 1510 cal. yr BP, April SIC oscillated around the mean value (55%) and during the time interval 1510–1120 cal. yr BP and after 650 cal. yr BP was above the mean, indicating more extensive sea-ice cover in Disko Bugt. Agreement between reconstructed April SIC and changes in the diatom species suggests that the sea-ice condition in Disko Bugt was strongly influenced by variations in the relative strength of two components of the West Greenland Current, i.e. the cold East Greenland Current and the relatively warm IC. Further analysis of the reconstructed SIC [sea ice change] record suggests that solar radiation may be an important forcing mechanism behind the historic sea-ice changes.
Introduction: Monsoon is a large-scale phenomenon of the seasonal cycle in various regions around the world and the associated precipitation changes are stronger in summer, i.e. June July August (JJA) over the Northern Hemisphere and December January February (DJF) over the Southern Hemisphere. Monsoon is also part of the global energetics and participates in the redistribution of heat and water across the two hemispheres as well as between land and ocean. Paleoclimate records and climate model simulations suggest that orbitally forced change in insolation was a major factor causing longer-term climate variations in the Holocene (e.g. Hewitt and Mitchell, 1998; Mitchell et al., 1988; Fleitmann et al., 2003, 2007; Mayewski et al., 2004; Gupta et al., 2005). Previous climate simulations (Weber et al., 2004) and proxy records (Staubwasser et al., 2003; Higginson and Altabet, 2004; Gupta et al., 2005; Selvaraj et al., 2007) have also shown that small (<1%) decadal to centennial scale solar irradiance can bring pronounced changes in the tropical monsoon during the Holocene. Accordingly, regional monsoon systems have undergone significant changes during the Holocene, and a common forcing mechanism (the Earth’s orbital precession cycle) has been proposed to underlie low latitude climate dynamics acting synchronously on the different monsoon sub-systems (Beaufort et al., 2010).
Energetic electron precipitation (EEP) from the Earth’s outer radiation belt continuously affects the chemical composition of the polar mesosphere. EEP can contribute to catalytic ozone loss in the mesosphere through ionization and enhanced production of odd hydrogen. However, the long-term mesospheric ozone variability caused by EEP has not been quantified or confirmed to date. Here we show, using observations from three different satellite instruments, that EEP events strongly affect ozone at 60–80 km, leading to extremely large (up to 90%) short-term ozone depletion. This impact is comparable to that of large, but much less frequent, solar proton events. On solar cycle timescales, we find that EEP causes ozone variations of up to 34% at 70–80 km. With such a magnitude, it is reasonable to suspect that EEP could be an important part of solar influence on the atmosphere and climate system.
The surface energy budget of the model during the melting periods [in Antarctica] showed that the net downwelling short-wave surface flux [the net solar energy at the surface] was the largest contributor to the melting energy, indicating that the cloud clearing effect of föhn events is likely to be the most important factor for increased melting relative to non-föhn days.
These coherent periodic modes match well with the 11-yr Schwabe sunspot cycle and 22-yr solar Hale cycle. The observed layering pattern is thus interpreted as recording solar induced climate changes that may have modulated microbial growth rate and biomass production in restricted subtidal environments on a broad epicontinental platform. The documented example represents the first reported solar signature in Mesoproterozoic marine carbonates and implies the sensitivity of microbial life to environmental changes prior to metazoan evolution.
Using 13 solar cycles (1869-2009) we study winter surface temperatures and North Atlantic oscillation (NAO) during four different phases of the sunspot cycle: minimum, ascending, maximum and declining phase. We find significant differences in the temperature patterns between the four cycle phases, which indicates a solar cycle modulation of winter surface temperatures.
Increased fresh meltwater input and early sea-ice retreat in spring under the solar irradiance maximum follow the positive phase of Arctic Oscillation which impacted the primary production and volume of upper intermediate water production in the following winter. Strength of this 11 year solar irradiance effect might be further regulated by the pressure patterns of Pacific decadal oscillation and/or El Niño-Southern Oscillation variability.
The cooling transition observed at the boundary between the Neoglacial and RWP [Roman Warm Period] in our study also agrees with the abrupt climate deterioration at 2800-2700 BP (also referred to as the Subboreal/Subatlantic transition) and therefore may have been driven by decreased solar radiation and weakened North Atlantic Oscillation conditions.
It is established that the climatic response in the tropospheric and sea surface temperature to the effect of solar and geomagnetic activity is characterised by a significant space-time irregularity and is local. A distinguishing feature of these distributions is the presence of regions of both positive and negative correlations. The exception is the epoch (1910-1940) when the SST response to geomagnetic activity was positive in virtually all regions, i. e. was global. This epoch coincides with the longest period of increase in geomagnetic activity during the period considered at the end of which annual averages of geomagnetic activity exceeded maximum values at the beginning of the epoch.
The impact of solar variations on particle formation and cloud condensation nuclei (CCN), a critical step for one of the possible solar indirect climate forcing pathways, is studied here. Our global simulations indicate that a decrease in ionization rate associated with galactic cosmic ray flux change from solar minimum to solar maximum reduces annual mean nucleation rates, number concentration of condensation nuclei larger than 10 nm (CN10), and number concentrations of CCN at water supersaturation ratio of 0.8% (CCN0.8) and 0.2% (CCN0.2) in the lower troposphere by 6.8%, 1.36%, 0.74%, and 0.43%, respectively. The inclusion of 0.2 C temperature increase enhances the CCN solar cycle signals by around 50%. The effect of solar cycle perturbation on CCN0.2 [cloud formation] based on present study is generally higher than those reported in several previous studies, up to around one order of magnitude.
Conclusion: [G]ravitational and electromagnetic planetary forces should modulate both solar activity and, directly or indirectly, the electromagnetic properties of the heliosphere. The climate could respond both to solar luminosity oscillations and to the electromagnetic oscillations of the heliosphere, and synchronize to them. The electromagnetic oscillations of the heliosphere and the interplanetary electric field could directly influence the Earth’s cloud system through a modulation of cosmic ray and solar wind causing oscillations in the terrestrial albedo, which could be sufficiently large (about 1-3%) to cause the observed climatic oscillations (e.g: Mörner, 2013; Scafetta, 2012a, 2013b; Svensmark, 2007; Tinsley, 2008; Voiculescu et al., 2013).
Phase-locked sequences are found in Pacific Ocean SST3.4 temperature data during the periods 1991–1999, 2002–2008 and in 2009–2013. These three sequences apparently being separated by climate shifts. It is asserted that the associated climate system is driven by a forcing of solar origin that has two manifestations: (1) A direct phase-locked response to what is identified as a solar forcing at a frequency of 1.0 cycle/yr for the whole time series; (2) A phase-locked response at either the second or third subharmonic of the putative solar forcing between 1991 and 1999; 2001–02 and 2008; and again between 2008 and 2013. This study confirms the results of  that some of the largest maxima/minima in the oscillations of the phase-locked state correspond to well-known El Niños/La Niñas.
Tibetan lake sediments have been extensively studied to understand past climate change in the Tibetan Plateau in NW China, especially during the Holocene. It is now well-established that the first half of the Holocene was largely warm (~11–~5 ka ago), but the climate generally became colder with a greater variability during the last ~5 ka. These climatic variations were largely driven by changes in the magnitudes of solar insolation and earth’s orbit. Kusai Lake sediments on the Northern Tibetan Plateau archive the solar insolation variations and the changes of the ocean-atmospheric circulation pattern since the last 3770 years. The overall climate in the Kusai Lake region was warm between ~3770–2550 years before the present (abbreviated as cal. yr BP hereafter, where the year 1950 AD was defined as the present), but gradually cooled between ~2550–2150 cal. yr BP, and became dry and cold in the last 2150 years. Four distinct winter monsoon periods were recognized and are coincident with the four well-recognized sunspot minima (Wolf, Spörer, Maunder, and Dalton).
Antarctic “Vostok” station works most closely to the center of the ice cap among permanent year-around stations. Climate conditions are exclusively stable: low precipitation level, cloudiness and wind velocity. These conditions can be considered as an ideal model laboratory to study the surface temperature response on solar irradiance variability during 11-year cycle of solar activity. Here we solve an inverse heat conductivity problem: calculate the boundary heat flux density (HFD) from known evolution of temperature. Using meteorological temperature record during (1958–2011) we calculated the HFD variation about 0.2–0.3 W/m2 in phase with solar activity cycle. This HFD [heat flux density] variation is derived from 0.5 to 1 °C temperature variation and shows relatively high climate sensitivity per 0.1 % of solar radiation change.
Motivated by numerous ground-based Noctilucent Cloud (NLC) sightings at latitudes as low as ~ 40oN in recent years, we have conducted a study to determine if there have been any systematic NLC increases in the mid-northern latitudes.. Results show a statistically significant increase in the number of PMCs [Polar Mesospheric Clouds] each season in the latitude range 40o-55oN for the past ten-year period examined [2002-2011]. Increases in cloud frequency appear to be driven by corresponding temperature decreases over the same time period. During this time, solar activity decreased from an active to a quiet period, which might have been partially responsible for the temperature decrease over this time period.
[T]he variability of the hemispheric tropospheric temperature is well connected to the Scandinavian Pattern, to the Pacific North American teleconnection and less with the North Atlantic Oscillation. There is also a possible link with the Southern Oscillation (SO) for winter. Solar UV and cosmic ray flux might influence tropospheric temperature during warm seasons, solar maximum or QBO West. Significant correlations between the Northern stratospheric temperature and the SO is observed especially during the Eastern phase of QBO and solar minimum. Signatures of geomagnetic variability are seen in the winter stratospheric temperature. The stratospheric temperature correlates with the cosmic ray flux and solar UV at annual level at solar maximum and QBO [Quasi-biennial oscillation] West.
An 11-year cycle of diatom and radiolarian flux peaks was identified from the laminated interval. Increased fresh meltwater input and early sea-ice retreat in spring under the solar irradiance maximum follow the positive phase of Arctic Oscillation which impacted the primary production and volume of upper intermediate water production in the following winter. Strength of this 11 year solar irradiance effect might be further regulated by the pressure patterns of Pacific decadal oscillation and/or El Niño-Southern Oscillation variability.
Geological archives have shown periods of abrupt climate change in the relatively stable Holocene epoch (last ca. 11700 years). One of these periods was around 2800 cal BP. Several records, mainly from Europe, reveal a shift towards wetter, cooler and windier conditions. There are, however, indications for a global extent of the climate change. The climate change [cooler] coincides with a distinct increase in the atmospheric radiocarbon (14C) concentration, which has been interpreted to be a result of decreased solar activity. Therefore, a solar-induced climate change has been suggested.
The recent extended minimum of solar and geomagnetic variability (XSM) mirrors the XSMs in the nineteenth and twentieth centuries: 1810–1830 and 1900–1910. Such extended minima also were evident in aurorae reported from 450 A.D. to 1450 A.D. This paper argues that these minima are consistent with minima of the Centennial Gleissberg Cycles (CGCs), a 90–100 year variation observed on the Sun, in the solar wind, at the Earth, and throughout the heliosphere.
Here we investigate North Atlantic Central Water circulation as a possible mechanism regulating the latitudinal temperature gradient (LTG), which, in turn, amplifies climate sensitivity to small changes in solar irradiance. Through this mechanism, sharp climate events and transitions are the result of a positive feedback process that propagates and amplifies climate events in the North Atlantic region. The presented records demonstrate the important role of ENACW [East North Atlantic Central Waters] circulation in propagating the climate signatures of the LTG by reducing the meridional heat transfer from high to low latitudes during the transition from the Holocene Thermal Maximum to the late-Holocene. In addition, the dynamic response of ENACW circulation to the gradual climate forcing of LTGs provides a prime example of an amplifying climate feedback mechanism.
Solar Brightening/Reduction in Cloud, Aerosols (Surface Solar Radiation) = Global Warming
Given that models overestimate the influence of carbon dioxide it follows that the relative accuracy of the models for the period 1950 to 1997, as reported in IPCC’s 4AR , could only occur if the models under estimated the influence of other forcings. One forcing that might have been underestimated is cloud cover. Variations in total solar irradiance are often discussed but not variations in cloud cover, but cloud cover impedes the flow of radiation, which in general means that it controls the amount of radiation reaching the Earth’s surface during the day, and how much heat is lost during overnight cooling. The reduction in total cloud cover of 6.8% [between 1984 – 2009] means that 5.4 Wm−2 (6.8% of 79) is no longer being reflected but acts instead as an extra forcing into the atmosphere. To put this [5.4 Wm-2 of solar radiative forcing via cloud cover reduction between 1984-2009] into context, the IPCC Fifth Assessment Report…states that the total anthropogenic radiative forcing for 2011 relative to 1750 is 2.29 Wm−2 for all greenhouse gases and for carbon dioxide alone is 1.68 Wm−2. The increase in radiative forcing caused by the reduction in total cloud cover over 10 years is therefore more than double the IPCC’s estimated radiative forcing for all greenhouse gases and more than three times greater than the forcing by carbon dioxide alone [from 1750 to present].
This study analyses the interannual variability of sunshine duration (SDU) at the urban area of Athens from 1897 to 2011. Observations of total cloud cover (TCC) are also used for a better interpretation of SDU variations. The annual SDU in Athens has increased by +8% (+19 h/decade) over the past century, mainly due to increase in the summer and spring SDU, however, distinct sub periods with decreasing and increasing trends are also discerned. SDU in Athens has undergone an abrupt increase during 1940s with early 1950s being the brightest period of the record. For long periods the course of SDU mirrors TCC, indicating a strong negative correlation between the two variables, nevertheless during the last three decades, both variables reveal trends of the same sign (more evident in spring). Under all-sky conditions, annual SDU decreased by approximately 7% from 1950s to 1980s and increased by 3% thereafter. Under clear sky conditions, the increase of SDU after 1980s is larger, amounting to 9%. Singular spectrum analysis and Continuous Wavelet Transform indicated significant non-linear trends of SDU and an intermittent oscillation, centered at 2.9–3.0 yrs.
Trends in downwelling global solar irradiance were evaluated at high elevation sites on the island of Maui, Hawai‘i. Departures from monthly means were assessed for the 6-month Hawaiian wet and dry seasons over the period 1988 to 2012. Linear regression analysis was used to characterize trends in each season. For the dry season (May-October), statistically significant (p ≤0.05) positive trends of 9–18 W m-2 (3–6%) per decade were found at all four high elevation stations tested [for 1988 to 2012]. Wet season trends were not significant, except at the highest elevation station, which had a significant negative trend. No consistent trends in aerosol concentrations have been observed at high elevations in Hawai‘i, therefore, the observed dry-season brightening is most likely the result of decreasing cloud cover. Supporting this hypothesis, analysis of 15 years (1997-2012) of high temporal resolution Geostationary Operational Environmental Satellite (GOES) imagery over the Hawaiian Islands showed a statistically significant decrease in leeward cloud cover amounting to 5–11% per decade over the stations. In addition, analysis of Moderate Resolution Imaging Spectroradiometer (MODIS) data were in general agreement with the GOES trends, although statistically significant dry-season trends were found at only one of the four stations.
The contribution of clouds and aerosols to the decadal variations of downward surface shortwave radiation (SSR) is a current controversial topic. This study proposes a method, which is based on surface-based SSR measurements, aerosol observations, and radiative transfer simulations (in cloud-free and cloud- and aerosol-free scenarios), to evaluate cloud-aerosol (CARE), cloud (CRE), and aerosol (ARE) radiative effects. This method is applied to quantify the role played by, separately, clouds and aerosols on the intense brightening of the SSR observed in the Iberian Peninsula. Clouds and Earth’s Radiation Energy Budget System (CERES) and surface-based data exhibit an increase in SSR between 2003 and 2012, exceeding +10 W m−2 over this period for some areas of the peninsula. The calculations are performed for three surface-based sites: Barcelona and Valladolid (Spain), and Évora (Portugal). Ranges in monthly values of CARE, CRE, and ARE are (−80, −20), (−60, −20), and (−30, 0), respectively (in W m−2). The average trends for the analyzed period of CARE, CRE, and ARE are +7, +5, and +2 W m−2 per decade, respectively. Overall, three fourths of the SSR trend is explained by clouds, while the other one fourth is related to aerosol changes. The SSR trends explained by the clouds and aerosol radiative effects are in line with the observed reductions in total cloud cover and aerosol load (both at the surface and in the whole atmospheric column). Furthermore, the CRE values are compared against CERES data showing good agreement between both data series, although some discrepancies are observed in their trends.
Concerning the global solar radiation, many publications agree on the existence of a solar dimming period between 1970 and 1985 and a subsequent solar brightening period (Norris and Wild, 2007; Solomon et al., 2007; Makowski et al., 2009; Stjern et al., 2009; Wild et al., 2009; Sanchez-Lorenzo and Wild, 2012). Different studies have calculated the trend in Sg after 1985. The trend in Sg [global solar radiation] from GEBA (Global Energy Balance Archive; between 1987 and 2002 is equal to +1.4 ( 3.4)Wm-2 per decade according to Norris and Wild (2007). Stjern et al. (2009) found a total change in the mean surface solar radiation trend over 11 stations in northern Europe of +4.4% between 1983 and 2003. In the Fourth Assessment Report of the IPCC (Solomon et al., 2007), 421 sites were analyzed; between 1992 and 2002, the change of all-sky surface solar radiation was equal to 0.66 Wm-2 per year. Wild et al. (2009) investigated the global solar radiation from 133 stations from GEBA/World Radiation Data Centre belonging to different regions in Europe. All series showed an increase over the entire period, with a pronounced upward tendency since 2000. For the Benelux region, the linear change between 1985 and 2005 is equal to +0.42 Wm-2 per year, compared to the pan-European average trend of +0.33Wm-2 per year (or +0.24Wm-2 if the anomaly of the 2003 heat wave is excluded) (Wild et al. 2009). Our trend at Uccle of +0.5 ( 0.2)Wm-2 per year [5 W/m-2 per decade] (or +4% per decade) agrees within the error bars with the results from Wild et al. (2009).
The annual sunshine duration mean time series shows a decrease from the early 1960s to the late 1970s [in Iran], in line with the widespread dimming of surface solar radiation observed during this period. By the early 1980s, there is an increase in sunshine through the end of the 20th century, aligning with a well-known and well-documented brightening period.
Total global solar shortwave (G) irradiation and sunshine duration were recorded at nine Spanish stations located in the Iberian Peninsula. Averaged series (using the nine locations) showed a statistically significant decrease in annual G [dimming] from 1950 to the mid 1980s (−1.7%dc−1) [-8.5 W/m2] together with a significant increase [brightening] from the mid 1980s to 2011 (1.6%dc−1) [+8 W/m2].
Results showed that DTR [daily temperature range] decreased rapidly (0.291 C/decade) from 1962 to 1989 [in China] due to slightly decreased Tmax [maximum temperatures] and significantly increased Tmin [minimum temperatures], but the decrease in DTR [daily temperature range] has stopped since 1990 as Tmax [maximum temperatures] and Tmin [minimum temperatures] kept pace with each other. During 1990-2011, DTR [daily temperature range] remained trendless, with slight increase in the 1990s and slight decrease after 2000. During the whole study period from 1962 to 2011, DTR [daily temperature range] decreased at a rate of 0.157 C/decade nationally. The changes in DTR [daily temperature range] were closely correlated with changes in sunshine duration (SD) in China except the Tibetan Plateau, suggesting that SD [sunshine duration] decrease is an important contributor to the decrease of DTR [daily temperature range] through its influence on Tmax [maximum temperatures].
The Carpathians are the longest mountain range in Europe and a geographic barrier between Central Europe, Eastern Europe, and the Balkans. To investigate the climate of the area, the CARPATCLIM project members collected, quality-checked, homogenized, harmonized, and interpolated daily data for 16 meteorological variables and many derived indicators related to the period 1961–2010….Temperature was found to increase in every season, in particular in the last three decades, confirming the trends occurring in Europe; wind speed decreased in every season; cloud cover and relative humidity decreased in spring, summer, and winter, and increased in autumn, while relative sunshine duration behaved in the opposite way [increased]; precipitation and surface air pressure showed no significant trend, though they increased slightly on an annual basis. We also discuss the correlation between the variables and we highlight that in the Carpathian Region positive and negative sunshine duration anomalies are highly correlated to the corresponding temperature anomalies during the global dimming (1960s and 1970s) and brightening (1990s and 2000s) periods.
Solar – Cosmic Climate Linkages
[D]ecreasing/increasing GCR [galactic cosmic ray] flux can influence the rainfall and the temperature. We speculate that the proposed hypothesis, based on the Indian climate data can be extended to whole tropical and sub-tropical belt, and that it may contribute to global temperature in a significant way. If correct, our hypothesis has important implication for the sun – climate link.
Increased Earth surface heating during solar maxima regulates integrated water vapor, cloud liquid water content, and rainfall.
- Solar control on [Indian Summer Monsoon] ISM rainfall, [cloud liquid water content] LWC and [integrated water vapor] IWV is observed over India during 1977–2012.
- Sun influences the formation clouds and rainfall activity through GCR [Galactic Cosmic Ray] mediation.
- Increased Earth surface heating during solar maxima regulates IWV, LWC and rainfall.
- SSN [Sunspot Number] shows both positive and negative correlation with LWC and ISM rainfall.
- Wavelet analyses also indicate a solar control on ISM rainfall, LWC & IWV over India.
These results can be regarded as the effect of cosmic factors on cloud covering in Abastumani, which in turn may have an influence on climatic variations
We have studied conditions in interplanetary space, which can have an influence on galactic cosmic ray (CR) and climate change. In this connection the solar wind and interplanetary magnetic field parameters and cosmic ray variations have been compared with geomagnetic activity represented by the equatorial Dst index from the beginning 1965 to the end of 2012. Dst index is commonly used as the solar wind–magnetosphere–ionosphere interaction characteristic. The important drivers in interplanetary medium which have effect on cosmic rays as CMEs (coronal mass ejections) and CIRs (corotating interaction regions) undergo very strong changes during their propagation to the Earth. Because of this CMEs, coronal holes and the solar spot numbers (SSN) do not adequately reflect peculiarities concerned with the solar wind arrival to 1 AU. Therefore, the geomagnetic indices have some inestimable advantage as continuous series other the irregular solar wind measurements. We have compared the yearly average variations of Dst index and the solar wind parameters with cosmic ray data from Moscow, Climax, and Haleakala neutron monitors during the solar cycles 20–23. The descending phases of these solar cycles (CSs) had the long-lasting solar wind high speed streams occurred frequently and were the primary contributors to the recurrent Dst variations. They also had effects on cosmic rays variations. We show that long-term Dst variations in these solar cycles were correlated with the cosmic ray count rate and can be used for study of CR variations. Global temperature variations in connection with evolution of Dst index and CR variations is discussed.
Natural Ocean Oscillation Climate Influence (34)
Rapid Arctic warming and sea-ice reduction in the Arctic Ocean are widely attributed to anthropogenic climate change. The Arctic warming exceeds the global average warming because of feedbacks that include sea-ice reduction4, 5 and other dynamical and radiative feedbacks. We find that the most prominent annual mean surface and tropospheric warming in the Arctic since 1979 has occurred in northeastern Canada and Greenland. In this region, much of the year-to-year temperature variability is associated with the leading mode of large-scale circulation variability in the North Atlantic, namely, the North Atlantic Oscillation. Here we show that the recent warming in this region is strongly associated with a negative trend in the North Atlantic Oscillation, which is a response to anomalous [natural] Rossby wave-train activity [planetary waves related to the Earth’s rotation] originating in the tropical Pacific. Atmospheric model experiments forced by prescribed tropical sea surface temperatures simulate the observed circulation changes and associated tropospheric and surface warming over northeastern Canada and Greenland. Experiments from the Coupled Model Intercomparison Project Phase 5 (ref. 16) models with prescribed anthropogenic forcing show no similar circulation changes related to the North Atlantic Oscillation or associated tropospheric warming. This suggests that a substantial portion of recent warming in the northeastern Canada and Greenland sector of the Arctic arises from unforced natural variability.
Model simulations predict a decrease of the AMOC in the 21st century in response to increasing greenhouse gases of the order of one half a Sverdrup per decade (IPCC, 2007). Our observations indicate that the actual change over the last decade is much greater. The magnitude of the observed changes suggests that they are a part of a cyclical change rather than being directly linked to the projected anthropogenic AMOC decrease. [O]ur observations…show no significant change in the Gulf Stream transport over the 2004–2012 period when the AMOC is decreasing. …. We have shown that there was a slowdown in the AMOC transport between 2004 and 2012 amounting to an average of −0.54 Sv yr−1 (95 % c.i. −0.08 to −0.99 Sv yr−1 ) at 26◦ N, and that this was primarily due to a strengthening of the southward flow in the upper 1100 m and a reduction of the southward transport of NADW below 3000 m. This trend is an order of magnitude larger than that predicted by climate models associated with global climate change scenarios, suggesting that this decrease represents decadal variability in the AMOC system rather than a response to climate change. Further observations from the 26◦ N array will in time allow a better understanding of decadal variability of the AMOC and its relationship to the climate of the North Atlantic region.
4.3 The atmospheric circulation: Many of the recent and historical periods of climatic warming in Europe have been explained by changes in atmospheric circulation. For instance, much of the warming that occurred in the late 20th century in Europe has been attributed to the increased number of winters with a high-index AO/NAO (Hurrell, 1995; Visbeck et al., 2001). High-index AO/NAO conditions are also thought to have occurred during the Medieval Climate Anomaly, providing a dynamic explanation for the winter warmth experienced over Europe at this time (Trouet et al., 2009). Similarly in summer, the increased occurrence of heat waves in recent years has been shown to be the result of anomalous atmospheric circulation associated with blocking anticyclones (Kysely and Huth, 2006). This pattern has also been shown to underlie summer warming on longer timescales in the late Holocene (Della-Marta et al., 2007; Trouet et al., 2012; Yiou et al., 2012). Changes in atmospheric circulation have a significant influence on European climate (Sepp and Jaagus, 2002; van Ulden and van Oldenborgh, 2006; Hoy et al., 2013), but many climate models have difficulty reproducing this aspect of modern climate (van Ulden and van Oldenborgh, 2006; Woollings, 2010; Kjellstrom et al., 2011; Brands et al., 2013). The warming in Europe during the mid-Holocene simulated in climate models differs fundamentally from that shown in the data, and indicates a high sensitivity in models to the effects of the amplified seasonal insolation cycle experienced at this time, showing greater warming (cooling) in summer (winter) in response to increased (decreased) summer (winter) insolation.
The hydrological cycle is expected to intensify in response to global warming. Yet, little unequivocal evidence of such an acceleration has been found on a global scale. This holds in particular for terrestrial evaporation, the crucial return flow of water from land to atmosphere. Here we use satellite observations to reveal that continental evaporation has increased in northern latitudes, at rates consistent with expectations derived from temperature trends. However, at the global scale, the dynamics of the El Niño/Southern Oscillation (ENSO) have dominated the multi-decadal variability. During El Niño, limitations in terrestrial moisture supply result in vegetation water stress and reduced evaporation in eastern and central Australia, southern Africa and eastern South America. The opposite situation occurs during La Niña. Our results suggest that recent multi-year declines in global average continental evaporation Future changes in continental evaporation will be determined by the response of ENSO to changes in global radiative forcing, which still remains highly uncertain.
The most intense El Niño episodes in more than a century occurred after the 1970s climate shift. Previous studies show that the characteristics of the El Niño-Southern Oscillation (ENSO) phenomenon changed synchronously with the shift, but the associated causes are not fully understood.
Our results imply that, if the GSA [Great Salinity Anomaly] has not an anthropogenic origin, as was suggested, then the tropical Pacific climate shift [which led to more intense El Ninos] has a natural origin.
The El Niño Southern Oscillation (ENSO) creates strong variations in sea surface temperature in the eastern equatorial Pacific, leading to major climatic and societal impacts. In particular, ENSO influences the yearly variations of tropical cyclone (TC) activities in both the Pacific and Atlantic basins through atmospheric dynamical factors such as vertical wind shear and stability. Until recently, however, the direct ocean thermal control of ENSO on TCs has not been taken into consideration because of an apparent mismatch in both timing and location: ENSO peaks in winter and its surface warming occurs mostly along the Equator, a region without TC activity. Here we show that El Niño—the warm phase of an ENSO cycle—effectively discharges heat into the eastern North Pacific basin two to three seasons after its wintertime peak, leading to intensified TCs. This basin is characterized by abundant TC activity and is the second most active TC region in the world. As a result of the time involved in ocean transport, El Niño’s equatorial subsurface ‘heat reservoir’, built up in boreal winter, appears in the eastern North Pacific several months later during peak TC season (boreal summer and autumn). By means of this delayed ocean transport mechanism, ENSO provides an additional heat supply favourable for the formation of strong hurricanes. This thermal control on intense TC variability has significant implications for seasonal predictions and long-term projections of TC activity over the eastern North Pacific.
The North Atlantic sea surface temperature exhibits fluctuations on the multidecadal time scale, a phenomenon known as the Atlantic Multidecadal Oscillation (AMO). This letter demonstrates that the multidecadal fluctuations of the wintertime North Atlantic Oscillation (NAO) are tied to the AMO, with an opposite-signed relationship between the polarities of the AMO and the NAO. Our statistical analyses suggest that the AMO signal precedes the NAO by 10–15 years with an interesting predictability window for decadal forecasting. The AMO footprint is also detected in the multidecadal variability of the intraseasonal weather regimes of the North Atlantic sector. This observational evidence is robust over the entire 20th century and it is supported by numerical experiments with an atmospheric global climate model. The simulations suggest that the AMO-related SST anomalies induce the atmospheric anomalies by shifting the atmospheric baroclinic zone over the North Atlantic basin. As in observations, the positive phase of the AMO results in more frequent negative NAO—and blocking episodes in winter that promote the occurrence of cold extreme temperatures over the eastern United States and Europe. Thus, it is plausible that the AMO plays a role in the recent resurgence of severe winter weather in these regions and that wintertime cold extremes will be promoted as long as the AMO remains positive.
We have recently suggested that the warming in the sea surface temperature (SST) since 1900, did not occur smoothly and slowly, but with two rapid shifts in 1925/1926 and 1987/1988, which are more obvious over the tropics and the northern midlatitudes. Apart from these shifts, most of the remaining SST variability can be explained by the El Niño Southern Oscillation and the Pacific Decadal Oscillation (PDO). Here, we provide evidence that the timing of these two SST shifts (around 60 years) corresponds well to the quasi-periodicity of many natural cycles, like that of the PDO, the global and Northern Hemisphere annual mean temperature, the Atlantic Multi-decadal Oscillation, the Inter-Tropical Convergence Zone, the Southwest US Drought data, the length of day, the air surface temperature, the Atlantic meridional overturning circulation and the change in the location of the centre of mass of the solar system. In addition, we show that there exists a strong seasonal link between SST and ENSO over the tropics and the NH midlatitudes, which becomes stronger in autumn of the Northern Hemisphere. Finally, we found that before and after each SST shift, the intrinsic properties of the SST time series obey stochastic dynamics, which is unaffected by the modulation of these two shifts. In particular, the SST fluctuations for the time period between the two SST shifts exhibit 1/f-type long-range correlations, which are frequently encountered in a large variety of natural systems. Our results have potential implications for future climate shifts and crossing tipping points due to an interaction of intrinsic climate cycles and anthropogenic greenhouse gas emissions.
This study presents a climate reconstruction utilizing a seasonally resolved 417-year oxygen-isotope record of tree rings from southern Georgia, United States (1580–1997 CE). Oxygen isotopes within the cellulose predominately reflect moisture source observed on a seasonal scale between earlywood and latewood growth. Signatures of large climate oscillations were captured in modern and subfossil wood. Spectral and wavelet transform analyses of seasonally resolved oxygen isotopes showed distinct periodicities coinciding with the Atlantic multidecadal oscillation and other major climate oscillation phenomena. Oxygen-isotope values in latewood growth revealed a significant correlation with North Atlantic sea surface temperature anomalies. This correlation suggests that the precipitation source was strongly influenced by fluctuations in the Atlantic multidecadal oscillation and teleconnections with other major climate phenomena such as the North Atlantic subtropical high-pressure system, El Niño Southern Oscillation, and Pacific Decadal Oscillation. These results emphasize the utility of oxygen isotopes in tree rings for revealing seasonal influences associated with major climate drivers over centuries and enhance our understanding of long-term climate behavior on a detailed scale.
In this paper, we present two time-series from the Nile Delta to probe both millennial and centennial-scale changes in deltaic hydrogeomorphology over the past 8000 years. In a global Holocene context, the long-term decrease in Nile Delta accretion rates is consistent with insolation-driven changes in the ‘monsoon pacemaker’, attested throughout the mid-latitude tropics. Using a second record we suggest that, at shorter timescales, many of the major phases of deltaic modification were mediated by climate events linked to El Niño Southern Oscillation- type (ENSO) variability.
At multi-centennial timescale, changes in thermohaline circulation, via freshwater content fluctuations, appear to be responsible for the coupling between dryness in Iberia and SST cooling in eastern North Atlantic subtropical gyre. In contrast, some Holocene events include centennial-scale oscillations (~100 years) marked by MF declines in southern Iberia concomitant with SST warming in the eastern North Atlantic subtropical gyre. This climatic pattern is similar to that observed at decadal timescale under the influence of the positive mode of the North Atlantic Oscillation (NAO). We suggest, therefore, that synchronous SW Iberian dryness and SST warming at centennial timescale could be explained by atmospheric fluctuations related to NAO changes.
We present sediment oxygen isotope records spanning the last two millennia from 10 lakes, as well as climate model simulations, indicating that the Little Ice Age was dry relative to the Medieval Climate Anomaly in much of the Pacific Northwest of North America. This pattern is consistent with observed associations between the El Niño–Southern Oscillation (ENSO), the Northern Annular Mode, and drought as well as with proxy-based reconstructions of Pacific and Atlantic ocean-atmosphere variations over the past 1000 years.
Periods of more frequent storm events over the two last centuries are analysed first in order to link these events with possible forcing mechanisms (North Atlantic Oscillation (NAO) and Atlantic Multidecadal Oscillation (AMO) modes) triggering the most destructive storms. Then, palaeostorm events are discussed at the Holocene scale, from 6000 yr BP to present, to verify the forcing mechanisms. Most recorded [storm] events appear to be linked with cooling episodes, mostly in winter, a transition to or from a negative winter NAO mode, a positive AMO mode. Extreme storms occur immediately prior to the ‘Medieval Warm Period’ (MWP). Maximum effects are reached prior to the onset of the MWP and during the Maunder and Dalton solar minima. Low storm activity occurred during the Spörer Minimum linked to an acceleration of the Atlantic Meridional Overturning Circulation (AMOC). Main storm triggers seem to correspond to a positive AMO mode with an unstable jetstream configuration driving a negative NAO. In this study, four specific weather configurations were defined to explain each type of recorded storminess. The strongest storms correspond to low AMO and decennial-negative NAO modes (e.g. ‘Little Ice Age’), or high AMO in association with dominant low NAO modes, as during the early Middle Age and present-day period. Fresh or warm oceans in association with a positive NAO mode are stormy but with very low sting storms frequency.
This study presents the first precisely dated, annually resolved, multiregional Arctica islandica chronologies from the North Sea which cover the time interval AD 1040–2010 and contain important information on supra-regional climatic conditions (sea surface temperature (SST), ocean productivity, wind stress). Shell growth varied periodically on timescales of 3–8, 12–16, 28–36, 50–80, and 120–240 years, possibly indicating a close association with the North Atlantic Oscillation, ocean-internal cycles of the North Atlantic controlled by ocean–atmosphere couplings, and the Atlantic Multi-Decadal Oscillation. Increased climatic instability, that is, stronger quasi-decadal variability, seems to be linked to the predominance of atmospheric forcings and some significantly decreased insolation phases (e.g. Spörer and Maunder Minima). Increased climatic variability of shorter timescales was also observed during some particularly warm phases or regime shifts (e.g. during the ‘Medieval Climate Anomaly’ and since c. 1970). More stable climatic conditions, that is, extended warm or cold periods (‘Medieval Climate Anomaly’, ‘Little Ice Age’), however, fell together with a predominance of multi-decadal oceanic cycles. Whether the sunspot number and the higher frequency climate variability are causally linked and which processes and mechanisms are required lie beyond this study.
- Late Holocene storminess in Bermuda is linked to North Atlantic cooling
- Coastal SSTs [sea surface temperatures] in Bermuda are linked to NAO [North Atlantic Oscillation] phasing over the late Holocene
North Atlantic climate archives provide evidence for increased storm activity during the Little Ice Age (150 to 600 calibrated years (cal years) B.P.) and centered at 1700 and 3000 cal years B.P., typically in centennial-scale sedimentary records. Meteorological (tropical versus extratropical storms) and climate forcings of this signal remain poorly understood, although variability in the North Atlantic Oscillation (NAO) or Atlantic Meridional Overturning Circulation (AMOC) are frequently hypothesized to be involved.
Florida climate in highly sensitive to both high and low latitude climate perturbations due to its latitudinal position surrounded by water masses that transport heat northward. A well-studied aspect is that middle Holocene conditions became significantly wetter in Florida, initiating widespread peat accumulation in the Everglades. This environmental change has been attributed to various climate forcings, such as migration of the Intertropical Convergence Zone (ITCZ), increases in tropical storm intensity, position of the Bermuda High, intensification of the El Niño Southern Oscillation (ENSO), and post glacial sea level rise (SLR). Discerning between these forcings is only possible with quantitative reconstructions from a transect of sites that are affected differentially. Application of a transfer function on a north-to-south gradient of pollen records from Florida lakes here shows that the pattern of increasing precipitation during the middle Holocene cannot be explained by SLR, but that ENSO intensification is an important contributing factor. Seasonal-resolved proxy records with improved age models are urgently needed to further solve these issues.
Late twentieth-century instrumental records reveal a persistent southward shift of the Southern Westerly Winds during austral summer and autumn associated with a positive trend of the Southern Annular Mode (SAM) and contemporaneous with glacial recession, steady increases in atmospheric temperatures and CO2 concentrations at a global scale. However, despite the clear importance of the SAM in the modern/future climate, very little is known regarding its behaviour during pre-Industrial times. Here we present a stratigraphic record from Lago Cipreses (51°S), southwestern Patagonia, that reveals recurrent ~200-year long dry/warm phases over the last three millennia, which we interpret as positive SAM-like states. These correspond in timing with the Industrial revolution [Current Warm Period], the Mediaeval Climate Anomaly, the Roman and Late Bronze Age Warm Periods and alternate with cold/wet multi-centennial phases in European palaeoclimate records. We conclude that SAM-like changes at centennial timescales in southwestern Patagonia represent in-phase interhemispheric coupling of palaeoclimate over the last 3,000 years through atmospheric teleconnections.
The teak record and PDO index correlate most significantly and positively during December–May, at r = 0.41 (0.002, n = 109). We generated composite climate anomalies for southern Asia and adjacent ocean areas during negative and positive PDO phases and above/below average teak growth for the May–September wet monsoon season. They show that negative (positive) PDO phases correspond to dry (wet) conditions, due to reduced (enhanced) moisture flux into central Myanmar. Multitaper Method (MTM) and Singular Spectrum Analysis (SSA) spectral analyses reveal considerable multidecadal variability over the past several centuries of the teak chronology, consistent with the PDO.
An extended reanalysis, a combination of observations and model output, is used to examine the spatial patterns of physical variables associated with the Atlantic Multidecadal Oscillation (AMO) from 1871 to 2008. The results are presented as anomalies during positive and negative phases of the AMO. As in previous studies, during positive (negative) AMO phases the sea surface temperature (SST) is anomalously warm (cold) over most of the North Atlantic, with the exception of the east coast of the United States. The atmospheric patterns, associated with the positive phase of the AMO, include anomalous low pressure over the Atlantic between 20°S and 50°N, cyclonic surface winds around the low, reduced wind speeds over the tropical Atlantic and enhanced precipitation in the eastern tropical Atlantic, with roughly opposite conditions during negative AMO phases. There are, however, substantial differences in the SST and the atmospheric anomalies between periods of the same phase, especially in the extratropics. Correlations between the AMO and air temperature anomalies are positive over much of the globe between 40°S and 50°N, with correlations exceeding 0.6 (~ 95% significance level) over the Maritime Continent and northern rim of the Pacific Ocean. Most of the sea level pressure (SLP) anomalies beyond the Atlantic are not statistically significant.
The surface of the world’s oceans has been warming since the beginning of industrialization. In addition to this, multidecadal sea surface temperature (SST) variations of internal origin exist. Evidence suggests that the North Atlantic Ocean exhibits the strongest multidecadal SST variations and that these variations are connected to the overturning circulation. This work investigates the extent to which these internal multidecadal variations have contributed to enhancing or diminishing the trend induced by the external radiative forcing, globally and in the North Atlantic. A model study is carried out wherein the analyses of a long control simulation with constant radiative forcing at preindustrial level and of an ensemble of simulations with historical forcing from 1850 until 2005 are combined. First, it is noted that global SST trends calculated from the different historical simulations are similar, while there is a large disagreement between the North Atlantic SST trends. Then the control simulation is analyzed, where a relationship between SST anomalies and anomalies in the Atlantic meridional overturning circulation (AMOC) for multidecadal and longer time scales is identified. This relationship enables the extraction of the AMOC-related SST variability from each individual member of the ensemble of historical simulations and then the calculation of the SST trends with the AMOC-related variability excluded. For the global SST trends this causes only a little difference while SST trends with AMOC-related variability excluded for the North Atlantic show closer agreement than with the AMOC-related variability included. From this it is concluded that AMOC [Atlantic meridional overturning circulation] variability has contributed significantly to North Atlantic SST trends since the mid nineteenth century.
The abyssal warming around Antarctica is one of the most prominent multidecadal signals of change in the global ocean. Here we investigate its dynamical impacts on the Atlantic Meridional Overturning Circulation (AMOC) by performing a set of experiments with the ocean-sea ice model NEMO-LIM2 at ½° horizontal resolution. The simulations suggest that the ongoing warming of Antarctic Bottom Water (AABW), already affecting much of the Southern Hemisphere with a rate of up to 0.05°C decade, has important implications for the large-scale meridional overturning circulation in the Atlantic Ocean. While the abyssal northward flow of AABW is weakening, we find the upper AMOC cell to progressively strengthen by 5–10% in response to deep density changes in the South Atlantic. The simulations suggest that the AABW-induced strengthening of the AMOC is already extending into the subtropical North Atlantic, implying that the process may counteract the projected decrease of the AMOC in the next decades.
Snow events are not a rare episode in Mediterranean area, especially in northern and hilly areas of Italy. However, snowfall occurring quasi-simultaneously in the whole peninsula is extraordinary. This study collects, reconstructs, and analyzes the extraordinary snowfall episodes that occurred simultaneously in the whole Italian peninsula since 1709. This is the longest snowfall time series in the central Mediterranean area. The data, obtained by several documentary sources (from ancient archival to online databases), have been analyzed using different statistical tests, in order to explore normality, homogeneity, and stationarity. The results are characterized by a time-series stationarity with a quasi 60- and 100-year-dominant oscillation. No clear trend in the snowfall episode records is found. The 60-year cycle roughly matches with global-scale oscillations linked to natural forces, such as the Atlantic Multidecadal Oscillation and the winter North Atlantic Oscillation.
The characteristics of multidecadal variability (MDV) in global land surface air temperature (SAT) are analyzed based on observations. The role of sea surface temperature (SST) variations in generating MDV in land SAT is assessed using atmospheric general circulation model simulations forced by observed SST. MDV in land SAT exhibits regional differences, with amplitude larger than 0.3 °C mainly over North America, East Asia, Northern Eurasia, Northern Africa and Greenland for the study period of 1902–2004. MDV can account for more than 30 % of long-term temperature variation during the last century in most regions, especially more than 50 % in parts of the above-mentioned regions. The SST-forced simulations reproduce the observed feature of zonal mean MDV in land SAT, though with weaker amplitude especially at the northern high-latitudes. Two types of MDV in land SAT, one of 60-year-timescale, mainly observed in the northern mid-high-latitude lands, and another of20–30-year-timescale, mainly observed in the low-latitude lands, are also well reproduced. The SST-forced MDV accounts for more than 40 % amplitude of observed MDV in most regions. Except for some sporadically distributed regions in central Eurasia, South America and Western Australia, the SST-forced multidecadal variations are well in-phase with observations. The Atlantic Multidecadal Oscillation and Pacific Decadal Oscillation signals are found dominant in MDV of both the observed and SST-forced land SAT, suggesting important roles of these oceanic oscillations in generating MDV in global land SAT.
PDO phase seems to be an important influence on spring temperatures in the northwest U.S. [E]astern temperature regimes in annual, winter, summer and fall temperatures are more coincident with cool and warm phase AMO regimes. Annual AMO values also correlate significantly with summer temperatures along the eastern seaboard and fall temperatures in the southwest.
El Niño Southern Oscillation (ENSO) is the most dominant interannual signal of climate variability and has a strong influence on climate over large parts of the world. In turn, it strongly influences many natural hazards (such as hurricanes and droughts) and their resulting socioeconomic impacts, including economic damage and loss of life.
The bidecadal to centennial climate shifts in the Pacific region during the MCA [Medieval Climate Anomaly] can be described in terms of the latitudinal extent of the tropics and the mean state of the Pacific Ocean region with respect to the persistence or frequency of either phase of the El Niño−Southern Oscillation (ENSO). Shifts in mean climate state result from a change in the timing and frequency of persistent seasonal summer−winter weather patterns, and storm frequency. For example, a shift to more El Niño-like (La Niña-like) climate involves a higher frequency of westerly (southeasterly) winds in the Southern Hemisphere tropics and, on a decadal scale, represents the occurrence of multiyear El Niño (La Niña) events, as seen in recent decades 1980–2000 (1950–1970). Similarly, a poleward expansion (equatorward contraction) of the tropics results in more (less) frequent, quasistationary anticyclones in the subtropics, and more (less) north– south (west–east) winds in the southwest Pacific. During A.D. 800–900 and A.D. 1000–1100, the centennial mean climate pattern resembles a shift to the Central Pacific (Modoki) El Niño pattern, with southwesterly wind fields over New Zealand, and anomalous westerly wind fields (trade wind reversals) over the Central Pacific, combined with a poleward tropics. The Pacific region during the intervening A.D. 900–1000 period was dominated by the El Niño pattern and equatorward tropics, where the westerly wind field anomalies are located in the western to central Pacific. From A.D. 1000-1300, the Pacific tradewinds were strengthened generally by the poleward expansion of the tropics and the related, persistent subtropical anticyclones, firstly located over eastern and southern Australia and the Tasman Sea before A.D. 1100, then later over New Zealand and eastward post-A.D. 1140. During A.D. 1140–1260, the Pacific was dominated by a shift in mean climate to the Central Pacific (Modoki) La Niña pattern, together with an intensification and poleward expansion of the subtropical anticyclone. The post-A.D. 1140 patterns impact the CEP via cool sea surface temperatures (SSTs) and drought in the tropical central Pacific, and bifurcation of tradewinds and surface currents in the vicinity of the Austral and Tuamotu Islands. Hence, the poleward expansion of the tropics during the MCA [Medieval Climate Anomaly] opened an anomalous climate window for off-wind sailing routes to the southwest Pacific extratropics, primarily New Zealand.
Of the rise in global atmospheric temperature over the past century, nearly 30% occurred between 1910 and 1940 when anthropogenic forcings were relatively weak. This early warming has been attributed to internal factors, such as natural climate variability in the Atlantic region, and external factors, such as solar variability and greenhouse gas emissions. However, the warming is too large to be explained by external factors alone and it precedes Atlantic warming by over a decade. For the late twentieth century, observations and climate model simulations suggest that Pacific trade winds can modulate global temperatures, but instrumental data are scarce in the early twentieth century. Here we present a westerly wind reconstruction (1894–1982) from seasonally resolved measurements of Mn/Ca ratios in a western Pacific coral that tracks interannual to multidecadal Pacific climate variability. We then reconstruct central Pacific temperatures using Sr/Ca ratios in a coral from Jarvis Island, and find that weak trade winds and warm temperatures coincide with rapid global warming from 1910 to 1940. In contrast, winds are stronger and temperatures cooler between 1940 and 1970, when global temperature rise slowed down. We suggest that variations in Pacific wind strength at decadal timescales significantly influence the rate of surface air temperature change.
http://www.nature.com/ncomms/2014/141208/ncomms6752/full/ncomms6752.html The Atlantic Meridional Overturning Circulation (AMOC) is a key component of the global climate system, responsible for a large fraction of the 1.3 PW northward heat transport in the Atlantic basin. Numerical modelling experiments suggest that without a vigorous AMOC, surface air temperature in the North Atlantic region would cool by around 1–3 °C, with enhanced local cooling of up to 8 °C in regions with large sea-ice changes. Substantial weakening of the AMOC would also cause a southward shift of the inter-tropical convergence zone, encouraging Sahelian drought, and dynamic changes in sea level of up to 80 cm along the coasts of North America and Europe.
[T]he millennial oscillation in the flow of the North Atlantic Drift reported by Bond et al. (1997) is proposed to be part of a 1500 yr intrinsic deep ocean oscillation. This oscillation involves the exchange of North Atlantic intermediate-level deep water (NADW) formed in the seas east of Greenland with Antarctic Bottom Water formed in a shallow-water zone at the edge of the Antarctic continent. The concept of NADW formation is already well known, with details of the sinking water flowing out of the Greenland Sea observed by Smethie et al. (2000) using chlorofluorocarbon tracers. The concept of Antarctic Bottom Water formation is also already well established. However, its modulation by the changing fraction of NADW in the Southern Ocean, which I infer from the analysis of Weyl (1968), has not been previously discussed. The modulated lower-salinity Antarctic Bottom Water that reaches the northern North Atlantic then provides negative feedback for the cyclic variation of NADW formation as proposed here. This causes the 1500 yr bipolar oscillation. The feedback suggests the possible sinusoidal character of the proposed oscillation model. The model is consistent with the cooling of the Little Ice Age (Lamb, 1972, 1995), and it also correctly predicts NASA’s observation of today’s record maximum area of winter sea ice on the Southern Ocean and the present observed record low rate of Antarctic Bottom Water production cited by Broecker (2000). The sinusoidal form of this conceptual model is therefore reinforced by both old and new data, and provides insights into world-wide climate change.
[F]rom the decadal to the secular scales (up to 110-year intervals) the tide gauge accelerations oscillate significantly from positive to negative values mostly following the PDO, AMO and NAO oscillations. In particular, the influence of a large quasi 60–70 year natural oscillation is clearly demonstrated in these records.
- Western N. America winter temperature reconstructions clearly detect ENSO patterns. •Early post-volcanic El Niño-like response is conditional on eruptions evaluated. •Clear and robust La Niña-like response occurs in Years 3–5 after eruption.
The cooling trend in the eastern tropical Pacific sea surface temperature (SST) during 1979–2008 is examined by using a wide variety of data sets for the ocean and atmosphere. The results show that the cooling trend is statistically significant at the 10% level out of the equator rather than along the equator. Diagnostic analysis indicates that the SST cooling in the eastern tropical Pacific is resulted from a competition of global warming mode, Interdecadal Pacific Oscillation (IPO) mode, and Atlantic Multidecadal Oscillation (AMO) mode. The cooling trend is preliminarily dominated by the phase transition of IPO from positive to negative phases in the year around 1998/1999, which overwhelms the effect of global warming in past three decades. Quantitative estimates based on the average of four different SST data sets indicate that the global warming mode offsets more than half of the cooling effect of IPO mode. The phase transition of AMO during 1990s causes a weak warming trend in the eastern tropical Pacific and partly weakens the cooling, making the trend along the equator less significant. Climate impacts associated with global warming mode, IPO mode, and AMO mode are further examined. The surface air temperature cooling over the eastern tropical Pacific, the easterly wind anomaly along the Pacific equator, the enhanced zonal gradient in sea level pressure over tropical Pacific, and the increased precipitation over the Asian monsoon region during 1979–2008 are dominated by the phase transition of IPO.
This paper offers three interdependent contributions to studies of climate variation: (1) the recognition and analysis of an intrinsic millennial oceanic oscillation that affects both Northern and Southern high latitude climates, (2) The recognition of an oceanographic switch to ice-free seas west of Greenland that explains the initiation of the Last Ice Age, and (3) an analysis of the effect of increasing salinity in the seas east of Greenland that suggests the possibility of the initiation of an ice age threshold climate in the near future. …the hypothesis that modern society’s activities might cause a repetition of the transition to an ice age threshold climate within one or two decades from 2013.
It is known that the western United States (US) precipitation displays a north-south contrast, i.e., the so-called “precipitation dipole,” during El Niño and La Niña winters. Furthermore, the Pacific Decadal Oscillation (PDO) has been known to modulate this precipitation dipole. However, the underlying physical mechanism regulating this modulation is not well understood. This study revisits previous studies and suggests a physical mechanism of precipitation dipole modulation based on the PDO-storm track relationship. We found that both jet stream and storm track tend to move northward (southward) over the North Pacific during negative (positive) PDO winters, contributing to the increase of precipitation over the northwestern (southwestern) US, respectively. This relationship is robust regardless of El Niño-Southern Oscillation (ENSO), possibly facilitating modulation of the precipitation dipole. Moreover, changes in oceanic baroclinicity associated with the PDO phase are suggested to be responsible for anchorage of storm tracks over the North Pacific.
Natural Variability (8)
MULTIDECADAL- TO CENTURY-SCALE CLIMATE VARIATIONS: Analyses of observed climate records during the twentieth century, the last ice age, and the Holocene, in conjunction with climate modeling results, suggest that pronounced multidecadal to century-scale variability can be produced internally by a number of different mechanisms.
CONCLUDING REMARKS: The climate response to external forcing—especially on regional scales—is strongly influenced by dynamical processes in both the ocean and the atmosphere. Moreover, the existence of strong natural multidecadal to centennial variability makes the detection of anthropogenic climate change a challenge. The presentations at the workshop dealt with the full range of processes that contribute to forced and free (also referred to as unforced or internal) multidecadal climate variability. This broader framing of climate change science is required for quantifying the societal risks of future climate change because the internal variability is so large that ignoring it may lead to false estimates of the climate’s sensitivity to anthropogenic forcing. It is also required for properly assessing the extent to which today’s weather, specifically the statistics of extreme weather events, is changing in response to human-induced climate change.
While internal climate variability is known to affect climate projections, its influence is often underappreciated and confused with model error. Why? In general, modeling centers contribute a small number of realizations to international climate model assessments (e.g., Coupled Model Intercomparison Project 5 (CMIP5)). As a result, model error and internal climate variability are difficult, and at times impossible, to disentangle. Early results demonstrate the substantial influence of internal climate variability on 20th–21st century climate trajectories. Global warming hiatus decades occur, similar to those recently observed. Internal climate variability alone can produce projection spread comparable to that in CMIP5.
Arctic temperatures have risen dramatically relative to lower latitudes in recent decades, with a common supposition being that sea ice declines are primarily responsible for amplified Arctic tropospheric warming. This conjecture is central to a hypothesis in which Arctic sea ice loss forms the beginning link of a causal-chain that includes weaker westerlies in mid-latitudes, more persistent and amplified mid-latitude waves, and more extreme weather. Through model experimentation, the first step in this chain is examined by quantifying contributions of various physical factors to October-December (OND) mean Arctic tropospheric warming since 1979. The results indicate that the main factors responsible for Arctic tropospheric warming are recent decadal fluctuations and long-term changes in sea surface temperatures (SSTs), both located outside the Arctic. Arctic sea ice decline is the largest contributor to near-surface Arctic temperature increases, but accounts for only about 20% of the magnitude of 1000-500hPa warming. These findings thus disconfirm the hypothesis that deep tropospheric warming in the Arctic during OND has resulted substantially from sea ice loss. Contributions of the same factors to recent mid-latitude climate trends are then examined. It is found that pronounced circulation changes over the North Atlantic and North Pacific result mainly from recent decadal ocean fluctuations and internal [natural] atmospheric variability, while effects of sea ice declines are very small. Therefore, a hypothesized causal chain of hemisphere-wide connections originating from Arctic sea ice loss is not supported.
Projected sea level trends of the representative concentration pathway 4.5 (RCP4.5) scenario for 20-, 50-, and 100-yr intervals grow from being largely dominated by internal variability on shorter time scales to being the dominant sea level signal on long time scales. The internal variability is estimated by calculating overlapping trends for the various time scales on the regional sea level control run output from each model. When compared to the ensemble spread of the RCP4.5 scenario trends, the internal variability remains a substantial portion of the spread even after 50 years.
We examine how physical factors spanning climate and weather contributed to record warmth [heat waves] over the central and eastern United States in March 2012, when daily temperature anomalies at many locations exceeded 20°C. Several lines of evidence strongly implicate natural variations as the primary cause for the extreme event. The 2012 temperature anomalies had a close analog in an exceptionally warm U.S. March occurring over 100 years earlier, providing observational evidence that an extreme event similar to March 2012 could be produced through natural variability alone. In addition, forcing associated with a strong Madden–Julian oscillation further increased the probability for extreme U.S. warmth and provided important additional predictive information on the timing and spatial pattern of temperature anomalies. The results indicate that the superposition of a strong natural variation similar to March 1910 on longterm warming of the magnitude observed would be sufficient to account for the record warm March 2012 U.S. temperatures. We conclude that the extreme warmth over the central and eastern United States in March 2012 resulted primarily from natural climate and weather variability— a substantial fraction of which was predictable.
After a decrease of SST [sea surface temperature] by about 1 °C during 1964–1975, most apparent in the northern tropical region, the entire tropical basin warmed up. That warming was the most substantial (>1 °C) in the eastern tropical ocean and in the longitudinal band of the intertropical convergence zone. Examining data sets of surface heat flux during the last few decades for the same region, we find that the SST warming was not a consequence of atmospheric heat flux forcing [greenhouse gases]. Conversely, we suggest that long-term SST warming drives changes in atmosphere parameters at the sea surface, most notably an increase in latent heat flux, and that an acceleration of the hydrological cycle induces a strengthening of the trade winds and an acceleration of the Hadley circulation. These trends are also accompanied by rising sea levels and upper ocean heat content over similar multi-decadal time scales in the tropical Atlantic. Though more work is needed to fully understand these long term trends, especially what happens from the mid-1970’s, it is likely that changes in ocean circulation involving some combination of the [natural] Atlantic meridional overtuning circulation [AMOC] and the subtropical cells are required to explain the observations.
No increase in global temperature variability despite changing regional patterns
Evidence from Greenland ice cores shows that year-to-year temperature variability was probably higher in some past cold periods, but there is considerable interest in determining whether global warming is increasing climate variability at present. This interest is motivated by an understanding that increased variability and resulting extreme weather conditions may be more difficult for society to adapt to than altered mean conditions. So far, however, in spite of suggestions of increased variability, there is considerable uncertainty as to whether it is occurring. Here we show that although fluctuations in annual temperature have indeed shown substantial geographical variation over the past few decades [1984-2006], the time-evolving standard deviation of globally averaged temperature anomalies has been stable. A feature of the changes has been a tendency for many regions of low variability to experience increases, which might contribute to the perception of increased climate volatility. The normalization of temperature anomalies creates the impression of larger relative overall increases, but our use of absolute values, which we argue is a more appropriate approach, reveals little change. Regionally, greater year-to-year changes recently occurred in much of North America and Europe. Many climate models predict that total variability will ultimately decrease under high greenhouse gas concentrations, possibly associated with reductions in sea-ice cover. Our findings contradict the view that a warming world will automatically be one of more overall climatic variation.
A holistic perspective on changing rainfall-driven flood risk is provided for the late 20th and early 21st centuries. Economic losses from floods have greatly increased, principally driven by the expanding exposure of assets at risk. It has not been possible to attribute rain-generated peak streamflow trends to anthropogenic climate change over the past several decades. Projected increases in the frequency and intensity of heavy rainfall, based on climate models, should contribute to increases in precipitation-generated local flooding (e.g. flash flooding and urban flooding). [T]his article is consistent with the recent IPCC SREX assessment finding that the impacts of climate change on flood characteristics are highly sensitive to the detailed nature of those changes and that presently we have only low confidence in numerical projections of changes in flood magnitude or frequency resulting from climate change.
Cloud Climate Forcing (6)
[I]n all cases, two rapid changes in the atmosphere can bring the outgoing longwave radiation at the top of the atmosphere almost exactly (a difference of 0% to 0.3%) to the observed pseudo-balance values of clear and cloudy skies. According to the true energy balance values, the slightly nonlinear cloud forcing would be -0.56 Wm-2 per 1% increase in cloudiness and -0.1 °C per 1% increase in cloudiness over the normal cloudiness range variation from 60% to 70%. According to this study, the commonly used cloud forcing in the units of W/m2 yields effects that are about 40% too low for the long-term cloudiness changes. Cloudiness changes could alone explain the global warming.
We will show that changes of relative humidity or low cloud cover explain the major changes in the global mean temperature. We will present the evidence of this argument using the observed relative humidity between years 1970 and 2011 and the observed low cloud cover between years 1983 and 2008. One percent increase in relative humidity or in low cloud cover decreases the temperature by 0.15 °C and 0.11 °C, respectively. In the time periods mentioned before the contribution of the CO2 increase was less than 10% to the total temperature change.
Analysis of the Angstrom-Prescott relationship between normalized values of global radiation and sunshine duration measured during the last 50 years made at five sites with a wide range of climate and aerosol emissions showed few significant differences in atmospheric transmissivity under clear or cloud-covered skies between years when global dimming occurred and years when global brightening was measured, nor in most cases were there any significant changes in the parameters or in their relationships to annual rates of fossil fuel combustion in the surrounding 1° cells. It is concluded that at the sites studied changes in cloud cover rather than anthropogenic aerosols emissions played the major role in determining solar dimming and brightening during the last half century and that there are reasons to suppose that these findings may have wider relevance.
A simple theoretical model is constructed to reveal the cause of the future warming patterns. The result shows that a much greater polar, rather than tropical, warming depends primarily on present-day mean SST and surface latent heat flux fields, and atmospheric longwave radiation feedback associated with cloud change further enhances this warming contrast. In the tropics, an El Niño–like warming over the Pacific and Atlantic arises from a similar process, while cloud feedback resulting from different cloud regimes between east and west ocean basins also plays a role. A dipole warming over the equatorial Indian Ocean is a response to weakened Walker circulation in the tropical Pacific.
Increases in Asian aerosol emissions have been suggested as one possible reason for the hiatus in global temperature increase during the past 15 years. We study the effect of sulphur and black carbon (BC) emission changes between 1996 and 2010 on the global energy balance. We find that the increased Asian emissions have had very little regional or global effects, while the emission reductions in Europe and the U.S. have caused a positive radiative forcing. In our simulations, the global-mean aerosol direct radiative effect changes by 0.06 W/m2 during 1996 to 2010, while the effective radiative forcing (ERF) is 0.42 W/m2. The rather large ERF arises mainly from changes in cloudiness, especially in Europe. In Asia, the BC warming due to sunlight absorption has largely offset the cooling caused by sulphate aerosols. Asian BC concentrations have increased by a nearly constant fraction at all altitudes, and thus, they warm the atmosphere also in cloudy conditions.
This study shows that the magnitude of global surface warming greatly depends on the meridional distribution of surface thermal forcing. An atmospheric model coupled to an aquaplanet slab mixed layer ocean is perturbed by prescribing heating to the ocean mixed layer. The heating is distributed uniformly globally or confined to narrow tropical or polar bands, and the amplitude is adjusted to ensure that the global mean remains the same for all cases. Since the tropical temperature is close to a moist adiabat, the prescribed heating leads to a maximized warming near the tropopause, whereas the polar warming is trapped near the surface because of strong atmospheric stability. Hence, the surface warming is more effectively damped by radiation in the tropics than in the polar region. As a result, the global surface temperature increase is weak (strong) when the given amount of heating is confined to the tropical (polar) band. The degree of this contrast is shown to depend on water vapor– and cloud–radiative feedbacks that alter the effective strength of prescribed thermal forcing.
Water Vapor and Climate (2)
Water vapor is the most important greenhouse gas. It plays a major role in the dynamics of atmospheric circulation, radiation exchange within the atmosphere, and climate variability. Knowledge of the distribution of water vapor is important for understanding climate change and global warming. In this study, radiosonde data from 1985 to 2012 were used to examine the monthly, interannual, and annual variations and trends of precipitable water vapor (PWV) in central Saudi Arabia in the city of Riyadh (24° 43′N; 46° 40′E, 764 m a.s.l.). The results revealed a clear seasonal cycle of PWV with a maximum during the summer months (June–August) and a minimum during the winter (December–February). This variation follows the mean monthly variation of air temperature. The PWV displays considerable variability at the interannual scale. We could not attribute the variations to the air temperature because no relationship was found between the two variables when the interannual variations were examined. Study of the annual variations of the PWV showed cyclic variations with a period of approximately 10–11 years. The two maximums and minimums were in 1996 and 2007 and 1989 and 2000, respectively. The results showed that the annual [precipitable water vapor] PWV values are anticorrelated with solar activity, represented by sunspot number, during solar cycles 22 and 23.
Each method shows that, on average, water vapour contributes approximately 96% of current greenhouse gas warming. Thus, the factors controlling the amount of water vapour in the air also control the earth’s temperature.
TOTAL BACK RADIATION OF ALL GHG Figure 7 is FAQ 1.1 Figure 1 from page 96 of AR4. It shows the radiation balance for the earth and that the back radiation of all of the greenhouse gases is 324 W m-2. This is the value used to calculate the RF [radiative forcing] of CO2 at 378 ppmv as (8.67/324)/100 = 2.7% back radiation of the total of all of the greenhouse gases
From Table 1, CO2 accounts for 2.7% of the global warming while all of the other gases account for approximately 0.7% for a total of approximately 3.4%. It becomes evident that, on average, water vapour accounts for approximately 96% of the current global [greenhouse effect] warming. This is an important finding because it leads to the conclusion that the factors controlling the average level of water vapour in the atmosphere also control atmospheric temperature.
[O]n average, each molecule of CO2 is surrounded by approximately 23 molecules of water vapour at ground level. … If the warming effect of water molecules and CO2 molecules were the same, then the contribution of CO2 would be (1/22.7) = 4.4% of that of water vapour. But from the previous section, water molecules are 1.6 times more effective at warming than CO2 molecules. Using this value and the ratio of 22.7:1, the contribution of CO2 to warming of the atmosphere is approximately (1/22.7)/1.6 = 2.8% of that of water vapour. As water vapour is approximately 96% of the total RF of all of the GHG, the contribution of CO2 is approximately 4% less than this, i.e., 2.69%. If the average RH were 60%, the contribution of CO2 would be ((1/27.4)/1.32) x 0.96 = 2.65%. For practical purposes, these values are the same as the 2.7% obtained by the quadratic model.
Volcanic Influence on Climate (4)
The millennial scale is analyzed applying a specific filtering method. In that scale, the climate is cool after 1200–1400 AD. This more or less steady period is suggested to be due to volcanic episodes, which reduced the northward heat transport in the North Atlantic. The century scale variation, on the other hand, is suggested to be due to internal [natural] oscillations in sea surface temperature (SST) and to be connected to variations in the Arctic sea ice. Specifically, these oscillations have caused an additional warming and cooling trend in Northern Fennoscandian temperatures before and after 1930’s, respectively.
The relatively muted warming of the surface and lower troposphere since 1998 has attracted considerable attention. One contributory factor to this “warming hiatus” is an increase in volcanically-induced cooling over the early 21st century. Here, we identify the signals of late 20th and early 21st century volcanic activity in multiple observed climate variables. Volcanic signals are statistically discernible in spatial averages of tropical and near-global SST, tropospheric temperature, net clear-sky short-wave radiation, and atmospheric water vapor. Signals of late 20th and early 21st century volcanic eruptions are also detectable in near-global averages of rainfall. In tropical-average rainfall, however, only a Pinatubo-caused drying signal is identifiable. Successful volcanic signal detection is critically dependent on removal of variability induced by the El Niño/Southern Oscillation (ENSO).
Satellite observations of aerosol optical depth (AOD) above 15 km have demonstrated that small-magnitude volcanic eruptions substantially perturb incoming solar radiation. Here we use lidar, AERONET and balloon-borne observations to provide evidence that currently available satellite databases neglect substantial amounts of volcanic aerosol between the tropopause and 15 km at mid to high latitudes, and therefore underestimate total radiative forcing resulting from the recent eruptions. Incorporating these estimates into a simple climate model, we determine the global volcanic aerosol forcing since 2000 to be −0.19 ± 0.09 Wm−2. This translates into an estimated global cooling of 0.05 to 0.12 °C. We conclude that recent volcanic events are responsible for more post-2000 cooling than is implied by satellite databases that neglect volcanic aerosol effects below 15 km.
Despite continued growth in atmospheric levels of greenhouse gases, global mean surface and tropospheric temperatures have shown slower warming since 1998 than previously. Possible explanations for the slow-down include internal climate variability, external cooling influences and observational errors. Several recent modelling studies have examined the contribution of early twenty-first-century volcanic eruptions to the muted surface warming. Here we present a detailed analysis of the impact of recent volcanic forcing on tropospheric temperature, based on observations as well as climate model simulations. We identify statistically significant correlations between observations of stratospheric aerosol optical depth and satellite-based estimates of both tropospheric temperature and short-wave fluxes at the top of the atmosphere. We show that climate model simulations without the effects of early twenty-first-century volcanic eruptions overestimate the tropospheric warming observed since 1998. In two simulations with more realistic volcanic influences following the 1991 Pinatubo eruption, differences between simulated and observed tropospheric temperature trends over the period 1998 to 2012 are up to 15% smaller, with large uncertainties in the magnitude of the effect. To reduce these uncertainties, better observations of eruption-specific properties of volcanic aerosols are needed, as well as improved representation of these eruption-specific properties in climate model simulations.
In 2012, a total of 22 state and extension climatologists were selected through a purposive sample to represent main outlets of publicly available and location-specific climate information in the region. Nineteen of these climatologists completed a pre-interview survey that included the climate change question (see Wilke 2013). Consistent with the many disciplinary scientists in the two USDA-NIFA projects, over 90% of the climatologists agreed that climate change is occurring while none believed that it is not occurring (Table 1). Fifty-three percent [10 of 19] attributed climate change primarily to human activities.
An online survey of about 1600 private and public agricultural advisors was conducted in 2012 in four states (Indiana, Iowa, Michigan and Nebraska) in the Midwestern United States. Three-quarters of these advisors believed that climate change is occurring, with 12% [197 of 1,605] of them believing that it is mostly caused by human activities (Table 1).
Extension educators are a unique set of agricultural advisors who serve to connect and translate research from universities to farmers in order to decrease risk to the farm enterprise and increase productive capacity and resilience. Typically, Extension educators have at least a Masters degree and are trained in agronomic sciences, which may not include climate sciences. Almost 75% of the Extension educators [239 respondents] believed in climate change, with over 19% [46 of 239] attributing climate change mostly to human activities (Table 1).
In the Earth atmosphere, methane gradually converts into carbon dioxide which, according to the conventional anthropogenic theory of global warming, is the main driver of global climate change. The authors investigated the greenhouse effect of methane and carbon dioxide in the atmosphere using their tested adiabatic model, which relates the global temperature of troposphere to the atmospheric pressure and solar activity. This model allows one to analyze the global temperature changes due to variations in mass and chemical composition of the atmosphere. Even significant releases of anthropogenic carbon dioxide and methane into the atmosphere do not change average parameters of the Earth’s heat regime and have no essential effect on the Earth’s climate. Thus, petroleum production and other anthropogenic activities resulting in accumulation of additional amounts of methane and carbon dioxide in the atmosphere have practically no effect on the Earth’s climate.
The residual fraction of anthropogenic CO2 emissions which has not been captured by carbon sinks and remains in the atmosphere, is estimated by two independent experimental methods which support each other: the 13C/12C ratio and the temperature-independent fraction of d(CO2)/dt on a yearly scale after subtraction of annual fluctuations the amplitude ratio of which reaches a factor as large as 7. The anthropogenic fraction is then used to evaluate the additional warming by analysis of its spectral contribution to the outgoing long-wavelength radiation (OLR) measured by infrared spectrometers embarked in satellites looking down. The anthropogenic CO2 additional warming extrapolated in 2100 is found lower than 0.1°C in the absence of feedbacks. The global temperature data are fitted with an oscillation of period 60 years added to a linear contribution. The data which support the 60-year cycle are summarized, in particular sea surface temperatures and sea level rise measured either by tide gauge or by satellite altimetry. The tiny anthropogenic warming appears consistent with the absence of any detectable change of slope of the 130-year-long linear contribution to the temperature data before and after the onset of large CO2 emissions.
Arguments put forth in favor of anthropogenic global warming (AGW) are frequently lacking in objectivity due to the use of imprecise terms and unwarranted extrapolations. A salient characteristic of such arguments is, moreover, the seemingly arbitrary attribution of causes to certain phenomena [Singer, 2012a]. As a result, such arguments run counter to the reasoning that is a hallmark of the scientific method. The purpose of this paper is to reason about some of those erroneous arguments in order to better inform people about pitfalls from a misuse of the scientific method in arguments about AGW.
http://iopscience.iop.org/1748-9326/9/11/114007/article Chronologies from 80 m or more below treeline show a change in climate response and do not correlate strongly with temperature-sensitive chronologies developed from trees growing at upper treeline. Rather, they more closely resemble lower elevation precipitation-sensitive chronologies. At the highest sites, trees on South-facing slopes grow faster than trees on North-facing slopes. High growth rates in the treeline South-facing trees have declined since the mid-1990s. This suggests the possibility that the climate-response of the highest South-facing trees may have changed and that temperature may no longer be the main limiting factor for growth on the South aspect. These results indicate that increasing warmth may lead to a divergence between tree growth and temperature at previously temperature-limited sites.
It is known that carbon dioxide emissions cause the Earth to warm, but no previous study has focused on examining how long it takes to reach maximum warming following a particular CO2 emission. Using conjoined results of carbon-cycle and physical-climate model intercomparison projects, we find the median time between an emission and maximum warming is 10.1 years.
Climate of the Past (23)
A well-expressed Medieval Climate Anomaly (A.D. 910–1257) occurred in NENA [North Eastern North America] before the A.D. 1257 Samalas [volcanic eruption] event. The warmest decades reconstructed by STREC occurred between A.D. 1141 and 1170 (positive anomalies ranging from 0.89 °C to 1.80 °C with respect to the last decade) and between A.D. 1061 and 1095 (0.87–1.19 °C). The confidence intervals of STREC for these two periods were almost all higher than the mean temperatures of the last decade. The amplitude and timing of the Medieval Climate Anomaly reconstructed by STREC also resemble the results of a pollen-based temperature reconstruction for the North American forest tundra, and closely correspond to a period of ice-cap melting in the Eastern Canadian Arctic. Collectively, these complementary data sources demonstrate that a major and prolonged climatic shift occurred over the NENA sector after a series of 13th century volcanic eruptions centered around the A.D. 1257 Samalas event. This shift marked the end of the Medieval Climate Anomaly and the beginning of the Little Ice Age in this sector. … Temperature anomalies ranged from −1.3 °C to −3.0 °C in response to the three strongest tropical [volcanic] eruptions of the last millennium (A.D. 1257, 1452/1453, and 1815). With about two cooling episodes per century lasting for 10–20 y with a consequent reduction in tree growth
[The below graph from the paper shows North Eastern North America was much warmer during the Medieval Warm Period than modern.]
The large-scale syntheses of global mean temperatures in IPCC fourth report suggested that the Northern Hemisphere temperature in the second half of the 20th century was likely the highest in at least the past 1,300 years and the 1990s was likely the warmest decade. However, this remains debated and the controversy is centered on whether temperatures during the recent half century were higher than those during the Medieval Climate Anomaly (MCA, AD 800–1300) and the Roman Warm Period (RWP, BC 200–AD 400), the most recent two natural warm periods of the late Holocene. Here the high resolution sea surface temperatures (SSTs) of two time windows around AD 990 (±40) and AD 50 (±40), which located in the MCA and RWP respectively, were reconstructed by the Sr/Ca ratio and δ 18O of Tradacna gigas shells from the northern South China Sea. The results suggested that the mean SSTs around AD 990 (±40) and AD 50 (±40) were 28.1 °C and 28.7 °C, 0.8 °C and 1.4 °C higher than that during AD 1994–2005, respectively. These records, together with the tree ring, lake sediment and literature records from the eastern China and northwest China, imply that the temperatures in recent decades do not seem to exceed the natural changes in MCA [Medieval Climate Anomaly], at least in eastern Asia from northwest China to northern SCS.
Holocene sea surface temperatures in the eastern Fram Strait are reconstructed based on Mg/Ca ratios measured on the planktic foraminifer Neogloboquadrina pachyderma(sin). The reconstructed sub sea surface temperatures (sSSTMg/Ca) fluctuate markedly during the earliest Holocene at ~11.7 and 10.5 kyr BP. This is probably in response to the varying presence of sea-ice and deglacial meltwater. Between ~10.5–7.9 kyr BP, the sSSTMg/Ca values are relatively high (~4°C) and more stable reflecting high insolation and intensified poleward advection of Atlantic Water. After 7.9 kyr BP, the sSSTMg/Ca values decline to an average of ~3°C throughout the mid-Holocene. These changes can be attributed to a combined effect of reduced poleward oceanic heat advection and a decline in insolation as well as a gradually increased influence of eastward migrating Arctic Water. The sSSTMg/Ca values increase and vary between 2.1°C and 5.8°C from ~2.7 kyr BP to the present. This warming is in contrast to declining late-Holocene insolation and may instead be explained by factors including increased advection of oceanic heat to the Arctic region possibly insulated beneath a widening freshwater layer in the northern North Atlantic in conjunction with a shift in calcification season and/or depth habitat of N. pachyderma (sin).
To determine the longterm sensitivity of the Greenland ice sheet to a warmer climate, we explored how the southern Greenland ice sheet responded to climatic changes the last 10,000 years and in particular the Holocene Thermal Maximum (HTM), when local atmospheric temperatures in Greenland were 2-4°C higher than the present. We have used a number of threshold lakes to show that the ice margin was retracted behind its present-day extent in all sectors for a limited period between ~7 and 5 cal. kyr BP and in most sectors also from ~1.5 to 1 cal. kyr BP, in response to higher atmospheric and ocean temperatures.
As a proxy for Holocene climate near the ice sheet margin, we reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland. Multi-proxy data from sediments in Two Move lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material from ∼6.5 to ∼1.9 cal ka BP in Two Move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake. … The fluctuations of Bregne ice cap were likely influenced by Northern Hemisphere summer insolation [surface solar radiation] throughout the Holocene and abrupt late Holocene cold events.
Pollen analysis of a 2 m deep sediment core from Khedla Quila Lake, Betul District (southwestern Madhya Pradesh), India has demonstrated the vegetation succession and climate change since the Late-Holocene. The pollen sequences have revealed that between 1416 and 506 cal BP (AD 534e1444), open mixed tropical deciduous forest comprising Madhuca indica, Sapotaceae, Holoptelea, Acacia, and Schleichera occupied the region under a warm and moderately humid climate, corresponding, to a certain extent, with the Medieval Warm Period (MWP) that is known between AD 740 and 1150 worldwide. Between 506 and 120 cal BP (AD 1444e1830), the open mixed tropical deciduous forest was succeeded by dense mixed tropical deciduous forest due to the prevalence of a warm and humid climate, coinciding with the Little Ice Age (LIA) which falls within the temporal range of AD 1450 and 1850 at global level. Since 120 cal BP to Present (AD 1830 onwards), the open mixed tropical deciduous forest again came into existence owing to a warm and less humid climate. The cereal-based agriculture practice continued at almost the same pace, but the lake widened during the second phase, which could be attributed to increased monsoon precipitation.
Little Ice Age (LIA) austral summer temperature anomalies were derived from palaeoequilibrium line altitudes at 22 cirque glacier sites across the Southern Alps of New Zealand. Modern analog seasons with temperature anomalies akin to the LIA reconstructions were selected, and then applied in a sampling of high-resolution gridded New Zealand climate data and global reanalysis data to generate LIA climate composites at local, regional and hemispheric scales. The composite anomaly patterns assist in improving our understanding of atmospheric circulation contributions to the LIA climate state, allow an interrogation of synoptic type frequency changes for the LIA relative to present, and provide a hemispheric context of the past conditions in New Zealand. An LIA summer temperature anomaly of −0.56 °C (±0.29 °C) for the Southern Alps based on palaeo-equilibrium lines compares well with local tree-ring reconstructions of austral summer temperature. … Associated land-based temperature and precipitation anomalies suggest both colder- and wetter-than-normal conditions were a pervasive component of the base climate state across New Zealand during the LIA, as were colder-than-normal Tasman Sea surface temperatures. Proxy temperature and circulation evidence were used to corroborate the spatially heterogeneous Southern Hemisphere composite z1000 and sea surface temperature patterns generated in this study. A comparison of the composites to climate mode archetypes suggests LIA summer climate and atmospheric circulation over New Zealand was driven by increased frequency of weak El Niño-Modoki in the tropical Pacific and negative Southern Annular Mode activity.
[The below graph from this paper shows that 20th/21st century temperatures in Antarctica have not fallen outside the range of natural variability for the last 12,000 years.]
The South Atlantic Subtropical Dipole index (SASD) is based on the distribution of SST in the South Atlantic and fits these criteria. It represents the dominant mode of variability of SST [sea surface temperatures] in the South Atlantic, which is modulated by changes in the position and intensity of the South Atlantic Subtropical High. Here we reconstructed an index of the South Atlantic Ocean SST (SASD-like) for the past twelve thousand years (the Holocene period) based on proxy-data.
[The below graph from this paper shows that 20th/21st century temperatures in the South Atlantic have not fallen outside the range of natural variability for the last 12,000 years.]
The Agulhas Current (AC) is the strongest western boundary current in the Southern Hemisphere and is key for weather and climate patterns, both regionally and globally. Its heat transfer into both the midlatitude South Indian Ocean and South Atlantic is of global significance. A new composite coral record (Ifaty and Tulear massive Porites corals), is linked to historical AC sea surface temperature (SST) instrumental data, showing robust correlations.
[The below graph from this paper shows that 20th/21st century temperatures in South Africa have not fallen outside the range of natural variability for the last 334 years; temperatures in 1800-1825 and 1850-1875 were similarly as warm as modern.]
http://gsabulletin.gsapubs.org/content/127/1-2/297.abstract Three marine sediment cores were collected along the length of the fjord axis of Barilari Bay, Graham Land, west Antarctic Peninsula (65°55′S, 64°43′W). Multi-proxy analytical results constrained by high-resolution geochronological methods (210Pb, radiocarbon, 137Cs) in concert with historical observations capture a record of Holocene paleoenvironmental variability. Our results suggest early and middle Holocene (>7022–2815 cal. [calibrated] yr B.P.) retreated glacial positions and seasonally open marine conditions with increased primary productivity. Climatic cooling increased sea ice coverage and decreased primary productivity during the Neoglacial (2815 to cal. 730 cal. yr B.P.). This climatic cooling culminated with glacial advance to maximum Holocene positions and expansion of a fjord-wide ice shelf during the Little Ice Age (LIA) (ca. 730–82 cal. yr B.P.). Seasonally open marine conditions were achieved and remnant ice shelves decayed within the context of recent rapid regional warming (82 cal. yr B.P. to present). Our findings agree with previously observed late Holocene cooling and glacial advance across the Antarctic Peninsula, suggesting that the LIA was a regionally significant event with few disparities in timing and magnitude. Comparison of the LIA Antarctic Peninsula record to the rest of the Southern Hemisphere demonstrates close synchronicity in the southeast Pacific and southern most Atlantic region but less coherence for the southwest Pacific and Indian Oceans. Comparisons with the Northern Hemisphere demonstrate that the LIA Antarctic Peninsula record was contemporaneous with pre-LIA cooling and sea ice expansion in the North Atlantic–Arctic, suggesting a global reach for these events.
Effect of Holocene climate and sea level changes on landform evolution and human habitation: Central Kerala, India
The Holocene deposit in the study area is composed mainly of sand and clay dominant sediments that fall within an age range between 5390 ± 140 yrs BP and 10,110 ± 80 yrs BP. The palynological and non – pollen palynomorphs in the sediments together with the textural and geochemical attributes indicate that Holocene sedimentation took place in the area under fluctuating environmental conditions with marked changes of climate and sea level. The northern part of the study area near Pattanam revealed multiple lines of evidence of human habitation which were subsequently buried under fluvio-marine sediments in the Late Holocene.
A glacial expansion occurred during the Mid Holocene (5.1±0.1 kyr), represented by a large push moraine that enclosed a unique ice mass at the foot of the Monte Perdido Massif. (4) A melting phase occurred at approximately 3.4±0.2 and 2.5±0.1kyr (Bronze/ Iron Ages) after one of the most important glacial advances of the Neoglacial period. (5) Another glacial expansion occurred during the Dark Age Cold Period (1.4–1.2 kyr), followed by a melting period during the Medieval Climate Anomaly. (6) The ‘LIA’ represented a clear stage of glacial expansion within the Marboré Cirque. Two different pulses of glaciation were detected, separated by a short retraction. The first pulse occurred most likely during the late 17th century or early 18th century (Maunder Minimum), whereas the second occurred between 1790 and AD 1830 (Dalton Minimum). A strong deglaciation process has affected the Marboré Cirque glaciers since the middle of the 19th century
Rapid early Holocene ice retreat in West Greenland
Our compilation of 10Be and 14C ages demonstrates that the ice sheet retreated from the outer-coast to the present ice margin between c. 11.4 and 10.4 cal. ka BP in the Godthåbsfjord system and between 10.7 ± 0.6 and 10.1 ± 0.4 ka ago in Buksefjord, whereas the coast at Sermilik became ice free at c. 10.5 cal. ka BP. We find no significant changes in the retreat rates between the deep Godthåbsfjord system and the Buksefjord-Sermilik region, which is characterized by only a few narrow and shallow fjords. However, deglaciation was initiated c. 700–900 years earlier in the Godthåbsfjord system indicating that the deep fjords probably triggered land-based deglaciation by dynamic ice loss leading to an overall rapid early Holocene ice retreat and drawdown of the ice sheet in West Greenland.
Earth’s climate system has been oscillating over the last million years between cold glacials and warm interglacials, leaving the imprints of their climate states in form of isotopes variations and chemical impurities in polar ice caps. … Based on the unique reconstructed age scale to unfold the stratigraphically disturbed part from about 2200 m depth downwards (NEEM community members, Nature, 2013), we are able to present the first Greenland chemistry record over the entire last interglacial, the so called Eemian period (about 128’000 to 115’000 years ago). As the Eemian is believed to have been 4 to 8 degrees C warmer than the modern climate, it can be used as an analogue for our present warming climate and, thus, contributes to a better understanding of processes causing natural variations.
The past few decades of climate warming have brought overall margin retreat to the Greenland Ice Sheet. In order to place recent and projected changes in context, we are undertaking a collaborative field-modeling study that aims to reconstruct the Holocene history of ice-margin fluctuation near Thule (~76.5°N, 68.7°W), and also along the North Ice Cap (NIC) in the Nunatarssuaq region (~76.7°N, 67.4°W). Fieldwork reported by Kelly et al. (2013) reveals that ice in the study areas was less extensive than at present ca. 4700 (GIS) and ca. 880 (NIC) cal. years BP, presumably in response to a warmer climate.
It is widely believed that the last glaciers in the British Isles disappeared at the end of the Younger Dryas stadial (12.9–11.7 cal. kyr BP). Here, we use a glacier–climate model driven by data from local weather stations to show for the first time that glaciers developed during the Little Ice Age (LIA) in the Cairngorm Mountains. Our model is forced from contemporary conditions by a realistic difference in mean annual air temperature of −1.5°C and an increase in annual precipitation of 10%, and confirmed by sensitivity analyses. These results are supported by the presence of small boulder moraines well within Younger Dryas ice limits, and by a dating programme on a moraine in one cirque. As a result, we argue that the last glaciers in the Cairngorm Mountains (and perhaps elsewhere in upland Britain) existed in the LIA within the last few hundred years, rather than during the Younger Dryas [~15,000 – 11,700 years ago].
Evidence from variations in sediment density, validated by changes in Ti concentrations, reveal glaciers remained present in the catchment following deglaciation prior to 11,300 cal BP, culminating in a Holocene maximum between 9.6 and 9.5 ka cal BP. Correspondence with freshwater pulses from Hudson Strait suggests that Early Holocene glacier advances were driven by the melting Laurentide Ice Sheet (LIS). We find that glaciers disappeared from the catchment between 7.4 and 6.7 ka cal BP, following a late Hypsithermal. Glacier reformation around 4250 cal BP marks the onset of the Neoglacial, supporting previous findings. Between 3380 and 3230 cal BP, we find evidence for a previously unreported centennial-scale glacier advance. Both events are concurrent with well-documented episodes of North Atlantic cooling. We argue that this brief forcing created suitable conditions for glaciers to reform in the catchment against a background of gradual orbital cooling. These findings highlight the climate-sensitivity of the small glaciers studied, which rapidly responded to climate shifts. The start of prolonged Neoglacial glacier activity commenced during the Little Ice Age (LIA) around 700 cal BP, in agreement with reported advances from other glaciers on Svalbard. In conclusion, this study proposes a three-stage Holocene climate history of Svalbard, successively driven by LIS meltwater pulses, episodic Atlantic cooling and declining summer insolation.
Conclusion: Most of the late Holocene, including the MCA [Medieval Climate Anomaly] was characterized by overall warmer and wetter regional conditions as lake sediment records suggest ice retreated. There is strong evidence of glacial advances during the LIA [Little Ie Age] in the Venezuelan Andes at locations with headwalls above w4600 m asl, providing additional evidence that it was both colder and wetter at this time. The Holocene glacial and lake level records from Venezuela do not clearly conform to the expected responses to local solar insolation forcing, suggesting additional factors, such as shifting oceanic mean-state temperatures were instrumental in driving the pattern of observed climate changes.
We present a 1200 year drought reconstruction for the European Alpine region based on carbon isotope variations of tree rings from living larch trees and historic timber. The carbon isotope fractionation at the study site is sensitive to summer precipitation, temperature, and [solar] irradiance, resulting in a stable and high correlation with a drought index for interannual to decadal frequencies and possibly beyond (r2 = 0.58 for 1901–2004, July/August). When combining this information with maximum latewood density-derived summer temperature, a strongly reduced occurrence of summer droughts during the warm A.D. 900–1200 period is evident, coinciding with the Medieval Climate Anomaly (MCA), with a shift to colder and drier conditions for the subsequent centuries. The warm-wet MCA contrasts strongly with the climate of the drought-prone warm phase of the recent decades, indicating different forcing mechanism for these two warm periods and pointing to beneficial conditions for agriculture and human well-being during the MCA in this region.
The response of Earth’s major climate systems to natural forcings during the last 2000 years can provide valuable insight into the affect that ongoing climate change may have on these systems. … New results from Laguna de Ubaque, a small moraine dammed lake at 2060 m ASL in the Eastern Cordillera of the Colombian Andes, suggest a reduction in Andean South American summer monsoon (SASM) rainfall during the Medieval Climate Anomaly (MCA; 900 to 1200 CE) that is consistent with other records from the Andes. During the Little Ice Age (LIA; 1450 to 1900 CE), Ubaque shows wet conditions between 1450 and 1600 CE and drier conditions from1600 to 1900 CE.
A comparison of the Medieval fjord hydrography and climate regime of the main Norse settlements in Greenland demonstrates important differences in the timing of sea-ice expansion and storminess when comparing the Western and Eastern Settlement regions. The Western Settlement, as well as the northern hunting grounds around Disko Bugt, had already experienced major climate deterioration in the first decades after AD 1200. This regime shift in West Greenland included an expansion of fjord and sea ice (“West Ice”) in coastal waters as well as a drastic atmospheric cooling and an increase in storminess, mainly in the summer season. In contrast, environmental conditions in the Eastern Settlement deteriorated notably later, i.e., around AD 1400. At that time, ice conditions became much more severe, whereas the previously prevailing strong wind activity decreased, which was coeval with a general decrease in aeolian activity in West Greenland, eastern Canada, and NW Iceland. Summer blockage of the fjord entrance by thick, multi-year sea ice (“Storisen”) is a specific feature of the Eastern Settlement area, whereas in the Western Settlement region, the West Ice would have threatened Norse sailing in late winter. We may thus conclude that by shortly after AD 1200 living conditions in the Western Settlement had already became less attractive due to adverse effects of the early, regional climate deterioration.
Norse populations populated Iceland around AD 870, and a little over a century later, historical accounts indicate that Erik the Red and his father Thorvald Asvaldsson left Iceland because they had been implicated in a homicide (Gad, 1970; Karlsson 2000). In AD 985, they settled in a land named Greenland which was previously discovered by the explorer Gunnbjörn Ulfsson sometime between AD 876–932 and named Greenland by Erik Thorvaldsson (known as Erik the Red) in order to distinguish it from Iceland, as well as to attract settlers (Massa, 2010). Less than two hundred years later, the population of Greenland had grown to several thousand inhabitants due to climate conditions that favored Viking agricultural and pastoral practices (McGovern, 1991). Viking populations were primarily distributed in two regions: the Eastern Settlement and the Western Settlement (Figure 1). Based on ecclesiastic records, we know that the Western settlement had been abandoned by AD 1350, and the last record that documents a Norse presence Greenland is a letter dated AD 1409, which announces a marriage that took place in AD 1408 (Gad, 1970). … Norse subsistence was principally based on livestock including cattle, sheep, goats, pigs and horses (Dugmore et al, 2012). While they did cultivate barley, corn spurrey (Spergula arvensis) and flax (Linum usitatissimum) (Fredskild and Humle 1991, Dugmore et al. 2012), most agricultural production focused on fodder used to feed cattle during the winter.
During the early stages of their occupation of Greenland, which occurred during the Medieval Warm Period (MWP), Norse populations practiced agriculture and pastoralism while their neighbors, the Inuits, subsisted on sea resources. Isotopic analyses and zooarchaelogical data indicate that, across all five centuries of their Greenland occupation, Norse populations did progressively adopt Inuit subsistence practices to a minor extent (Arneborg et al., 1999, 2012; McGovern et al., 2006). However, as pointed out by several authors, on the whole, Viking populations did not significantly modify their sedentary, production-based lifestyle, and continued as much as possible their ‘cultural intransigence’ (Barlow et al., 1997); i.e., agrarian production combined with livestock grazing. … Numerous climate records indicate that between AD 1350 and AD 1850 the climate deteriorated, and this period is termed the Little Ice Age (LIA). This severe climatic deterioration disturbed the Norse economy (Dansgaard et al., 1975; Dugmore et al., 2007), adversely affecting agricultural productivity due to dry winds (Lassen et al., 2004) and rising sea levels (Mikkelsen et al., 2008). These climatic changes also adversely affected trade since sea ice off southeastern Greenland significantly expanded and made shipping between Iceland and Greenland difficult (Kuijpers, et al., 1999).
Contaminated Temperature Records (2)
New Zealand provides a rare long temperature time series in the Southern Hemisphere, and it is one of the longest continuous climate series available in the Southern Hemisphere Pacific. It is therefore important that this temperature dataset meets the highest quality control standardsNew Zealand’s national record for the period 1909 to 2009 is analysed and the data homogenized. Current New Zealand century-long climatology based on 1981 methods produces a trend of 0.91 °C per century. Our analysis, which uses updated measurement techniques and corrects for shelter-contaminated data, produces a trend of 0.28 °C per century.
Daily minimum temperature (Tmin) and maximum temperature (Tmax) data of Huairou station in Beijing from 1960 to 2008 are examined and adjusted for inhomogeneities by applying the data of two nearby reference stations. Urban effects on the linear trends of the original and adjusted temperature series are estimated and compared. Results show that relocations of station cause obvious discontinuities in the data series, and one of the discontinuities for Tmin are highly significant when the station was moved from downtown to suburb in 1996. The daily Tmin and Tmax data are adjusted for the inhomogeneities. The mean annual Tmin and Tmax at Huairou station drop by 1.377°C and 0.271°C respectively after homogenization.
Ocean Acidification (7)
The state of the world’s seas is often painted as verging on catastrophe. But although some challenges are very real, others have been vastly overstated, researchers claim in a review paper. The team writes that scientists, journals and the media have fallen into a mode of groupthink that can damage the credibility of the ocean sciences. The controversial study exposes fault lines in the marine-science community. Carlos Duarte, a marine biologist at the University of Western Australia in Perth, and his colleagues say that gloomy media reports about ocean issues such as invasive species and coral die-offs are not always based on actual observations. It is not just journalists who are to blame, they maintain: the marine research community “may not have remained sufficiently sceptical” on the topic.
http://link.springer.com/article/10.1007%2Fs00338-014-1241-3 This study investigated the response of the gorgonian coral Eunicea fusca to a range of CO2 concentrations from 285 to 4,568 ppm (pH range 8.1–7.1) over a 4-week period. Gorgonian growth and calcification were measured at each level of CO2 as linear extension rate and percent change in buoyant weight and calcein incorporation in individual sclerites, respectively. In general, growth and calcification did not stop in any of the concentrations of pCO2… These results highlight the susceptibility of the gorgonian coral E. fusca to elevated levels of carbon dioxide but suggest that E. fusca could still survive well in mid-term ocean acidification conditions expected by the end of this century, which provides important information on the effects of ocean acidification on the dynamics of coral reef communities.
[T]here have been a few claims for already realized impacts of ocean acidification on calcifiers, such as a decline in the number of oysters on the West Coast of North America (Barton et al. 2012) and in Chesapeake Bay (Waldbusser et al. 2011). However, the link between these declines and ocean acidification through anthropogenic CO2 is unclear. Corrosive waters affecting oysters in hatcheries along the Oregon coast were associated with upwelling (Barton et al. 2012), not anthropogenic CO2. The decline in pH affecting oysters in Chesapeake Bay (Waldbusser et al. 2011) was not attributable to anthropogenic CO2 but was likely attributable to excess respiration associated with eutrophication. Therefore, there is, as yet, no robust evidence for realized severe disruptions of marine socioecological links from ocean acidification to anthropogenic CO2, and there are significant uncertainties regarding the level of pH change that would prompt such impacts.
[O]n the basis of a survey of the scientific literature, Oliver and colleagues (2009) identified four global coral bleaching events (1983, 1987, 1998, and 2005) when the bleaching frequency and intensity dramatically affected a substantial number of countries. However, the number of bleaching records has apparently increased during the past three decades, which has confounded efforts to separate changes in bleaching frequency from changes in reporting (Oliver et al 2009). Therefore, despite the strong mechanistic or physiological basis for a role of warming in coral bleaching and coral growth, a robust demonstration of a direct causal link between global warming and global coral bleaching over decadal time scales has not yet been produced.
Todd and colleagues (2010) reported high rates of miscitation in the marine biology literature, with only 75.8% of citations clearly supporting the assertions made. This assessment refers to miscitations of past research, but citation biases can also derive from selective citations. Selective citations are described by authors’ tendencies to report the evidence that corresponds with their preconceived ideas while discarding contradictory results.
Calcifying foraminifera are expected to be endangered by ocean acidification; however, the response of a complete community kept in natural sediment and over multiple generations under controlled laboratory conditions has not been constrained to date. During 6 months of incubation, foraminiferal assemblages were kept and treated in natural sediment with pCO2-enriched seawater of 430, 907, 1865 and 3247 [ppm] μatm pCO2. The fauna was dominated by Ammonia aomoriensis and Elphidium species, whereas agglutinated species were rare. After 6 months of incubation, pore water alkalinity was much higher in comparison to the overlying seawater. Consequently, the saturation state of Ωcalc was much higher in the sediment than in the water column in nearly all pCO2 treatments and remained close to saturation. As a result, the life cycle (population density, growth and reproduction) of living assemblages varied markedly during the experimental period, but was largely unaffected by the [ppm] pCO2 treatments applied.
[T]he principal proximate causes of the loss of hermatypic corals have been attributed to storm damage, coral bleaching events, widespread growth of corallivores (e.g., crown-of-thorns starfish, COTS), and coral skeletal diseases (CSDs). [I]t is now widely accepted that the lack of recovery of the reefs and the proliferation of COTS are largely attributable to eutrophication [localized water pollution] … [E]vidence is emerging that CSDs and coral bleaching are also promoted by eutrophication.
Corals play a key role in ocean ecosystems and carbonate balance but their molecular response to ocean acidification remains unclear. The only previous whole transcriptome study (Moya et al. 2012) documented extensive disruption of gene expression, particularly of genes encoding skeletal organic matrix proteins, in juvenile corals (A. millepora) after short-term (3 d) exposure to elevated pCO2. In the present study, whole transcriptome analysis was used to compare the effects of such “acute” (3 d) exposure to elevated pCO2 with a longer (“prolonged”; 9 d) period of exposure beginning immediately post-fertilisation. The most obvious feature of the molecular response in the 9 d treatment experiment was the up-regulation of five distinct Bcl-2 family members, the majority predicted to be anti-apoptotic. This suggests that an important component of the longer-term response to elevated CO2 is suppression of apoptosis. It therefore appears that juvenile A. millepora [corals] have the capacity to rapidly acclimate to elevated pCO2, a process mediated by up-regulation of specific HSPs and a suite of Bcl-2 family members.
Reef corals are highly sensitive to heat, yet populations resistant to climate change have recently been identified. To determine the mechanisms of temperature tolerance, we reciprocally transplanted corals between reef sites experiencing distinct temperature regimes and tested subsequent physiological and gene expression profiles. Local acclimatization and fixed effects, such as adaptation, contributed about equally to heat tolerance and are reflected in patterns of gene expression. In less than 2 years, acclimatization achieves the same heat tolerance that we would expect from strong natural selection over many generations for these long-lived organisms. Our results show both short-term acclimatory and longer-term adaptive acquisition of climate resistance. Adding these adaptive abilities to ecosystem models is likely to slow predictions of demise for coral reef ecosystems.
Sea Level Rise (14)
- GMSL [global mean sea levels] started decelerated rising since 2004 with rising rate 1.8 ± 0.9 mm/yr in 2012.
- Deceleration is due to slowdown of ocean thermal expansion during last decade.
- Recent ENSO events introduce large uncertainty of long-term trend estimation.
Here we investigate the global-mean sea level (GMSL) change during 1993–2012 using Empirical Mode Decomposition, in an attempt to distinguish the trend over this period from the interannual variability. It is found that the GMSL rises with the rate of 3.2 ± 0.4 mm/yr during 1993–2003 and started decelerating since 2004 to a rate of 1.8 ± 0.9 mm/yr in 2012. This deceleration is mainly due to the slowdown of ocean thermal expansion in the Pacific during the last decade
We study the longest tide gauge record available from Greenland, that is the Nuuk/Godthab site in southwest Greenland, for the time period 1958–2002. Standard regression methods and the application of the Ensemble Empirical Mode Decomposition technique reveal a rate of sea-level rise of ≈ 2 mm yr− 1, two complete cycles of the 18.6-years lunar nodal tide, and a negligible acceleration. Using previous assessments for the globally averaged sea-level rise during that period, glacial isostatic adjustment modeling and sea-level “fingerprinting” of the mass loss of continental ice sources, terrestrial water sources and oceanic steric effects, we evaluate the various contributions to local sea-level rise at the tide gauge location. The misfit between the observed and the modeled sea-level trend is unlikely to reflect tectonic deformations but, more intriguingly, may indicate that the mass balance of the Greenland ice sheets was, during the second half of the last century, somehow closer to balance than suggested by previous investigations.
Despite the two independent methods [GRACE and residual] covering different time periods with differing spatial and temporal resolution, they both capture the same large-scale mass addition trend patterns including higher rates of mass addition in the North Pacific, South Atlantic, and the Indo-Atlantic sector of the Southern Ocean, and lower mass addition trends in the Indian, North Atlantic, South Pacific, and the Pacific sector of the Southern Ocean. The global mean trend of ocean mass addition is 1.5 (±0.4) mm yr for 1996–2006 from the residual method and the same for 2003–2013 from the GRACE method.
Since the early 1990s, sea level rose at a mean rate of ~3.1 mm yr. However, over the last decade a slowdown of this rate, of about 30%, has been recorded. It coincides with a plateau in Earth’s mean surface temperature evolution, known as the recent pause in warming
http://onlinelibrary.wiley.com/doi/10.1002/2014GC005272/abstract Upon correction for isostatic island subsidence, we find that local relative sea level was at least ~1.5±0.4 m higher than present at ~5,400 years ago.
The distribution of prehistoric cultures was closely related with Holocene sea-level fluctuations, especially on the banks of Hangzhou Bay, where the distribution changes of prehistoric cultural sites were greatly affected by sea-level changes, with the closest relationships between them. After 7000 cal. a BP, the process of lowered sea-level and regression-epeirogenesis provided wider terrestrial living spaces for prehistoric inhabitants.
[I]n the Maqiao cultural period, cultural sites were greatly reduced in the coastal lowland of eastern Jiaxing and northeast Hangzhou. This might be related to a sea-level rise event between 4000-3000 cal. a BP (Chen et al., 2008).
Deep-ocean contribution to sea level and energy budget not detectable over the past decade
As the dominant reservoir of heat uptake in the climate system, the world’s oceans provide a critical measure of global climate change. Here, we infer deep-ocean warming in the context of global sea-level rise and Earth’s energy budget between January 2005 and December 2013. Direct measurements of ocean warming above 2,000 m depth explain about 32% of the observed annual rate of global mean sea-level rise. Over the entire water column, independent estimates of ocean warming yield a contribution of 0.77 ± 0.28 mm yr−1 in sea-level rise and agree with the upper-ocean estimate to within the estimated uncertainties. Accounting for additional possible systematic uncertainties, the deep ocean (below 2,000 m) contributes −0.13 ± 0.72 mm yr−1 to global sea-level rise and −0.08 ± 0.43 W m−2 to Earth’s energy balance. The net warming of the ocean implies an energy imbalance for the Earth of 0.64 ± 0.44 W m−2 from 2005 to 2013.
Finally, a global reconstruction of sea level (Jevrejeva et al. in Geophys Res Lett 35:L08715, 2008) and a reconstruction of the North Atlantic Oscillation (NAO) index (Luterbacher et al. in Geophys Res Lett 26:2745–2748, 1999) are analyzed and compared: both sequences cover about three centuries from 1700 to 2000. The proposed methodology quickly highlights oscillations and teleconnections among the records at the decadal and multidecadal scales. At the secular time scales tide gauge records present relatively small (positive or negative) accelerations, as found in other studies (Houston and Dean in J Coast Res 27:409–417, 2011). On the contrary, from the decadal to the secular scales (up to 110-year intervals) the tide gauge accelerations oscillate significantly from positive to negative values mostly following the PDO, AMO and NAO oscillations. In particular, the influence of a large quasi 60–70 year natural oscillation is clearly demonstrated in these records. The multiscale dynamical evolutions of the rate and of the amplitude of the annual seasonal cycle of the chosen six tide gauge records are also studied.
We therefore study individual tide gauge data on sea levels from the Permanent Service for Mean Sea Level (PSMSL) during 1807 – 2010 without recourse to data reconstruction. Although mean sea levels are rising by 1 mm/year, sea level rise is local rather than global, and is concentrated in the Baltic and Adriatic seas, South East Asia and the Atlantic coast of the United States. In these locations, covering 35 percent of tide gauges, sea levels rose on average by 3.8mm/year. Sea levels were stable in locations covered by 61 percent of tide gauges, and sea levels fell in locations covered by 4 percent of tide gauges. In these locations sea levels fell on average by almost 6mm/year.
Highlights: Sea levels are oscillating with important multidecadal periodicities. Sea levels are not presently positively accelerating worldwide. Sea levels are presently decreasing in Norway and not positively accelerating. Sea level rises from 16 to 116 cm by 2100 in Norway are unrealistic.
This paper shows that despite today’s most popular climate models indicating that sea levels are generally rising and accelerating and that the coastal management in Norway may face sea level rises from 16 to 116 cm by the year 2100, all the local and global tide gauges and the satellite radar altimeter reconstruction of global mean sea level consistently show that there is no accelerating behaviour, with negative sea level rises for the specific of Norway because of the post-glacial rebound. This suggests the sea level rise of this century will very likely be the one from the past century.
Global mean sea level change since 1900 is found to be 1.77 ± 0.38 mm year on average [less than 7 inches per century]. Although the acceleration found for the global mean, +0.0042 ± 0.0092 mm year, is not significant, local values range from -0.1 mm year in the central Indian Ocean to +0.1 mm year in the western tropical Pacific and east of Japan.
Even if sea levels fluctuate with decadal and multi decadal periodicities about a linear trend without any positive acceleration component, many papers continue to compare different compilations of tide gauges of different length and different locations or assemble selected tide gauges of selected length and location to prove that sea levels are accelerating in Australia and elsewhere in the world when they are not. … It is proposed here a novel procedure fitting the tide gauge data with linear and multiple sinus functions that also iteratively completes the gaps in the recorded data with subsequent guess of the fitted function. It is shown that the tide gauges of Sydney and Fremantle, the only two exceeding a century in Australia, are acceleration free and naturally oscillating with different periodicities, phases and amplitudes for the Indian and Pacific Ocean locations. It is also shown that tide gauge records of length smaller than 60 years have rates of rise differing considerably from the legitimate long term trends, and these values may change significantly from an update to the other because of the natural oscillations.
Tide gauge records are the primary source of sea level information over multi-decadal to century timescales. A critical issue in using this type of data to determine global climate-related contributions to sea level change concerns the vertical motion of the land upon which the gauges are grounded. Here we use observations from the Global Positioning System for the correction of this vertical land motion. As a result, the spatial coherence in the rates of sea level change during the 20th century is highlighted at the local and the regional scales, ultimately revealing a clearly distinct behavior between the northern and the southern hemispheres with values of 2.0 mm/year and 1.1 mm/year, respectively [1.55 mm/year globally, or 6.1 inches per century]. Our findings challenge the widely accepted value of global sea level rise for the 20th century.
Sea levels generally oscillate with multi-decadal periodicities worldwide with up to the quasi-60 years detected in many tide gauges. Nevertheless, the most part of the literature on sea levels computes apparent rates of rise of sea levels much larger than the legitimate by using short time windows in selected locations only covering part of a valley-to-peak of this multi-decadal oscillation. It is shown in this paper that along the Pacific coast of Australia the sea levels oscillate with a frequency close to the Southern Ocean Index (SOI) oscillation of 19 years and a lower frequency of about 60 years. The rates of rise of sea levels computed by linear fitting of the data recorded since the early 1990s in selected locations of the Australian Pacific coastline and in the tropical Pacific islands are from a valley of the peak and valley oscillations and are much higher than the legitimate long term values.
Glaciers, Ice Sheets, and Sea Ice (10)
Even though the rise of global mean air temperature accelerated in the 20th century, the mass loss rate of glaciers during the second half of the 20th century was not higher than during the first half of the century (Leclercq et al., 2011; Marzeion et al., 2012).
The data set contains the glacier length records for 471 [global] glaciers and it covers the period 1535–2011. There are glacier length records from all continents and at almost all latitudes. For the observed glaciers, the 20th century retreat was strongest in the first half of the 20th century.…. [T]he retreat is strongest in the period 1921–1960 rather than in the last period 1961–2000, with a median retreat rate of 12.5 m yr in 1921–1960 and 7.4 m yr in the period 1961–2000. [Globally, glaciers melted 69% more rapidly from 1921-1960 than from 1961-2000.]
We present the first proxy record of sea-ice area (SIA) in the Ross Sea, Antarctica, from a 130 year coastal ice-core record. High-resolution deuterium excess data show prevailing stable SIA from the 1880s until the 1950s, a 2–5% reduction from the mid-1950s to the early-1990s, and a 5% increase after 1993. Additional support for this reconstruction is derived from ice-core methanesulphonic acid concentrations and whaling records. While SIA has continued to decline around much of the West Antarctic coastline since the 1950s, concurrent with increasing air and ocean temperatures, the underlying trend is masked in the Ross Sea by a switch to positive SIA anomalies since the early-1990s. This increase is associated with a strengthening of southerly winds and the enhanced northward advection of sea ice.
Two thousand and eighteen glaciers representing climatically diverse terrains in the Himalaya were mapped and monitored. It includes glaciers of Karakoram, Himachal, Zanskar, Uttarakhand, Nepal and Sikkim regions. Among these, 1752 glaciers (86.8%) were observed having stable fronts (no change in the snout position and area of ablation zone), 248 (12.3%) exhibited retreat and 18 (0.9%) of them exhibited advancement of snout. The net loss in 10,250.68 sq. km area of the 2018 glaciers put together was found to be 20.94 sq. km or 0.2%.
The change of ice thickness and velocity in the ice shelf [East Antarctica] is mainly influenced by the basal melt distribution, but, although the ice shelf thins in most of the simulations, there is little grounding line retreat. We find that the Lambert Glacier grounding line can retreat as much as 40 km if there is sufficient thinning of the ice shelf south of Clemence Massif, but the ocean model does not provide sufficiently high melt rates in that region. Overall, the increased accumulation computed by the atmosphere models outweighs ice stream acceleration so that the net contribution to sea level rise is negative.
The average snow accumulation rate [East Antarctica] calculated between volcanic stratigraphic horizons for the period AD 1260–2010 is 20.9 mm H2O [per year]. Positive (+13%) anomalies of snow accumulation were found for AD 1661–1815 and AD 1992–2010, and negative (−12%) for AD 1260–1601. We hypothesized that the changes in snow accumulation are associated with regional peculiarities in atmospheric transport.
Arctic Ocean sea ice proxies generally suggest a reduction in sea ice during parts of the early and middle Holocene (∼6000–10,000 years BP) compared to present day conditions. This sea ice minimum has been attributed to the northern hemisphere Early Holocene Insolation Maximum (EHIM) associated with Earth’s orbital cycles. Here we investigate the transient effect of insolation variations during the final part of the last glaciation and the Holocene by means of continuous climate simulations with the coupled atmosphere–sea ice–ocean column model CCAM. We show that the increased insolation during EHIM has the potential to push the Arctic Ocean sea ice cover into a regime dominated by seasonal ice, i.e. ice free summers. The strong sea ice thickness response is caused by the positive sea ice albedo feedback. Studies of the GRIP ice cores and high latitude North Atlantic sediment cores show that the Bølling–Allerød period (c. 12,700–14,700 years BP) was a climatically unstable period in the northern high latitudes and we speculate that this instability may be linked to dual stability modes of the Arctic sea ice cover characterized by e.g. transitions between periods with and without perennial sea ice cover.
Here we present three-dimensional (3D) floe-scale maps of sea-ice draft for ten floes, compiled from two springtime expeditions by an autonomous underwater vehicle to the near-coastal regions of the Weddell, Bellingshausen, and Wilkes Land sectors of Antarctica. Mean drafts range from 1.4 to 5.5 m, with maxima up to 16 m. We also find that, on average, 76% of the ice volume is deformed [thick] ice. Our surveys indicate that the floes are much thicker and more deformed than reported by most drilling and ship-based measurements of Antarctic sea ice. We suggest that thick ice in the near-coastal and interior pack may be under-represented in existing in situ assessments of Antarctic sea ice and hence, on average, Antarctic sea ice may be thicker than previously thought.
Geothermal Heat Flux Melts Antarctic Ice
One major contributor to fast glacial flow is the presence of subglacial water, the production of which is a result of both glaciological shear heating and geothermal heat flux. A zone of thinner crust is also identified near the area’s subaerial volcanoes lending support to a recent interpretation predicting that this part of Marie Byrd Land is a major volcanic dome, likely within the West Antarctic Rift System itself. [W]e prefer the hypothesis that Marie Byrd Land volcanoes are thermally-supported by warmer upper mantle. The presence of such inferred warm upper mantle also suggests regionally elevated geothermal heat flux in this sector of the West Antarctic Rift System and consequently the potential for enhanced meltwater production beneath parts of Thwaites Glacier itself.
Heterogeneous geothermal flux and subglacial volcanism have the potential to modulate ice sheet behavior and stability by providing a large, variable supply of meltwater to the subglacial water system, lubricating and accelerating the overlying ice. … Thwaites Glacier is one of the largest, most rapidly changing glaciers on Earth, and its landward sloping bed reaches into the deep interior of the WAIS [West Antarctic Ice Sheet], making it a leading component in scenarios for rapid deglaciation. … [H]eterogeneous geothermal flux beneath Thwaites Glacier is likely a significant factor in local, regional, and continental-scale ice sheet stability.
Oceans, Missing Heat, Regional Cooling (7)
Highlights •Results of climate models are in striking contrast with measurements. •Since 2004 deep ocean water salinities and temperatures have changed minimally. •Since 2000 sea ice extent has increased and surface air temperatures reduced.
Increasing ocean heat content has been suggested on the basis of theories. Reconstructions (modelling results based on selected scattered measurements) and simulations (modelling results not based on observations) have both shown a significant warming since the year 1970 that increased at an ever faster rate over the 14 years this century. It is shown here that, contrary to this claim, the detailed measurements of the ocean temperature and salinity by the sampling buoys of the ARGO project show only minor changes of temperature and salinity since the early 2000s. The ARGO results cover the ocean layers 0–2000 m except for the North and South Poles. The satellite NSSTC surface air temperature measurements over the world oceans show a global cooling over the last 11 years, and the satellite NSDIC sea ice extent measurements show globally increasing ice coverage over the North and South Poles. The North Pole sea ice is certainly reducing, but over the last 11 years the growth of the South Pole sea ice has more than compensated that loss. The true measurements are in marked contrast to theoretical reconstructions and simulations. This result has a huge implication on coastal management that should be based on observationally derived forecasts rather than “projections” of models lacking validation.
In the 1960s and early 1970s, sea surface temperatures in the North Atlantic Ocean cooled rapidly. There is still considerable uncertainty about the causes of this event, although various mechanisms have been proposed. There is strong evidence that changes in atmospheric circulation, linked to a southward shift of the Atlantic ITCZ, played an important role in the event, particularly in the period 1972–76. Theories for the cooling event must account for its distinctive space–time evolution.
In the 1960s North Atlantic sea surface temperatures (SST) cooled rapidly. The magnitude of the cooling was largest in the North Atlantic subpolar gyre (SPG), and was coincident with a rapid freshening of the SPG. … We show that initialisation of an anomalously weak Atlantic Meridional Overturning Circulation (AMOC), and hence weak northward heat transport, is crucial for DePreSys to predict the magnitude of the observed cooling. Such an anomalously weak AMOC is not captured when ocean observations are not assimilated (i.e. it is not a forced response in this model). The freshening of the SPG is also dominated by ocean salt transport changes in DePreSys; in particular, the simulation of advective freshwater anomalies analogous to the Great Salinity Anomaly were key. Therefore, DePreSys suggests that ocean dynamics played an important role in the cooling of the North Atlantic in the 1960s, and that this event was predictable.
The observed 5 year mean temperature averaged over the upper 500 m of the SPG [Subpolar Gyre, North Atlantic Ocean) is shown in Figure 1a (red and blue shading [above]). There is a marked cooling in the late 1960s followed by a period with below average temperatures, and a warming in the 1990s followed by a period with above average temperatures. The SPG has been cooling slightly since the mid-2000s, but remains well above average. The grand ensemble 5 year hindcasts that were intialized between 1960 and 2007 (diamonds) show high skill in predicting the decadal variability of the observations (Pearson’s correlation r= 0.87, p <<0.001 with the effects of autocorrelation taken into account) consistent with previous studies [Robson et al., 2012b,2014b]. The forecasts that were initialized between 2008 and 2012 (crosses) all show a general trend for further decreases in temperature, continuing the observed [cooling] trend. The 2012 forecast spread suggests that the chance of the observed warm SPG mean temperature anomaly of 2003–2007 (0.53) occurring again in 2013–2017 is less than 6%.
To gain further confidence in this forecast we examine the physical mechanisms that control SPG [North Atlantic Ocean] temperatures. Previous studies showed that the 1990s SPG warming was driven by increased convergence of ocean heat transport resulting from an increase in the AMOC [Robson et al., 2012b; Yeager et al., 2012], and the 1960s cooling was driven by reduced ocean heat transport convergence following a reduced AMOC [Robson et al., 2014b]. The hindcasts show changes in ocean heat transport convergence, consistent with these earlier events. We find that changes in ocean heat transport convergence are skilfully predicted by the hindcasts (Figure 1b, diamonds; r = 0.86, p << 0.001, assessed against the convergence in the assimilation). The forecasts show a continued decrease in ocean heat transport convergence, consistent with a cooling SPG.
Discussion: Over the 20 yr of the present ECCO state estimate, changes in the deep ocean on multiyear time scales are dominated by the western Atlantic basin and Southern Oceans. These are qualitatively consistent with expectations there of the comparatively rapid response to surface forcing. Defining the physics of those changes in terms of boundary currents, wave propagation, eddy diffusion, and the myriad of other oceanic physical processes, region by region, remains a major unfinished piece of business. In those same regions, a longer-term general warming pattern occurs below 2000 m. A very weak long-term cooling is seen over the bulk of the rest of the ocean below that depth, including the entirety of the Pacific and Indian Oceans, along with the eastern Atlantic basin. … The globally integrated heat content changes involve small differences of the much larger regional changes. As existing estimates of the anthropogenic forcing are now about 0.5 W m−2, the equivalent global ocean average temperature changes over 20 yr are mostly slight compared to the shorter-term temporal variations from numerous physical sources. Small errors in data calibration, and space–time sampling and model biases, are important. Direct determination of changes in oceanic heat content over the last 20 yr are not in conflict with estimates of the radiative forcing, but the uncertainties in all the fields remain too large to rationalize, for example, the apparent pause in warming.
This study compares the distribution of surface climate trends over the Southern Ocean in austral summer between 1979–2011 and 1950–1978, using a wide variety of data sets including uninterpolated gridded marine archives, land station data, reanalysis, and satellite products. Apart from the Antarctic Peninsula and adjacent regions, sea surface temperatures and surface air temperatures decreased during 1979–2011, consistent with the expansion of Antarctic sea ice. In contrast, the Southern Ocean and coastal Antarctica warmed during 1950–1978. Sea level pressure (SLP) and zonal wind trends provide additional evidence for a sign reversal between the two periods, with cooling (warming) accompanied by stronger (weaker) westerlies and lower (higher) SLP at polar latitudes in the early (late) period. Such physically consistent trends across a range of independently measured parameters provide robust evidence for multidecadal climate variability over the Southern Ocean and place the recent Antarctic sea ice trends into a broader context. … For the Southern Ocean as a whole, sea surface temperature has decreased by approximately 0.6°C in December-February (0.4°C in the annual mean) while Antarctic sea ice cover has increased by approximately 9% in December-February (12% in the annual mean) during 1979-2011.
The sea level projection of a 1 meter rise for the 21st century depends on climate models that have projected a given amount of anthropogenic warming during the same period. However, these same climate models predicted a warming also from 2000 to 2014, which has not been seen in the global surface temperature. Researchers have proposed several solutions such as the fact that the “missing heat” was accumulated in the deep ocean. However, no evidences of a sufficient warming of the deep oceans have been observed. Other arguments has been proposed as well and found unsatisfactory. There is the opportunity that the “heat” is not “real” but “missing” or “hiding” somewhere. If the climate model projected “heat” that simply does not exist in reality in the first place, consequently the models overestimate the anthropogenic warming and also the sea level projections for the 21st century are overestimated.
Erroneous/Biased Climate Models and the Pause (12)
Globally, the general trend of increasing air surface temperature over the last 15 years has slowed in recent years, and is currently four times less than predicted by simulations [of the latest IPCC climate models] (Fyfe et al., 2013). However, over the same interval, global atmospheric CO2 level has continued to increase (Francey et al., 2013) and the Arctic Ocean has experienced a rapid decline in summer sea ice extent and thickness (Stroeve et al., 2012) (Fig. 1). The lack of a strong correlation between global average air temperature, atmospheric CO2 and Arctic summer sea ice provides one example that shows that Arctic environmental changes are heavily influenced by complex interplays between different feedback mechanisms.
The significant discrepancy between the Holocene global cooling inferred from proxy reconstructions and simulated warming in climate models reflects the Holocene temperature conundrum, which poses an important test for our understanding of climate changes and for the evaluation of climate models of their climate sensitivity to GHGs, ice sheets, orbital insolation, and volcanic forcings. Given the current uncertainties in both the reconstruction and model sensitivity, however, this model-data discrepancy could be attributed to either the seasonal bias in the SST reconstructions or the model bias in regional and seasonal climate sensitivity. If the M13 [Marcott, 2013] reconstruction is correct, it will imply major biases across the current generation of climate models. To provide a credible benchmark for future climate models, however, the proxy reconstructions will also need to be reexamined critically.
Idealized climate modeling studies often choose to neglect spatiotemporal variations in solar radiation, but doing so comes with an important decision about how to average solar radiation in space and time. Since both clear-sky and cloud albedo are increasing functions of the solar zenith angle, one can choose an absorption-weighted zenith angle that reproduces the spatial- or time-mean absorbed solar radiation. Calculations are performed for a pure scattering atmosphere and with a more detailed radiative transfer model and show that the absorption-weighted zenith angle is usually between the daytime-weighted and insolation-weighted zenith angles but much closer to the insolation-weighted zenith angle in most cases, especially if clouds are responsible for much of the shortwave reflection. Use of daytime-average zenith angle may lead to a high bias in planetary albedo of approximately 3%, equivalent to a deficit in shortwave absorption of approximately 10 W m−2 in the global energy budget (comparable to the radiative forcing of a roughly sixfold change in CO2 concentration). Other studies that have used general circulation models with spatially constant insolation have underestimated the global-mean zenith angle, with a consequent low bias in planetary albedo of approximately 2%–6% or a surplus in shortwave absorption of approximately 7–20 W m−2 in the global energy budget.
A recent temperature reconstruction of global annual temperature shows Early Holocene warmth followed by a cooling trend through the Middle to Late Holocene [Marcott SA, et al., 2013, Science 339(6124):1198–1201]. This global cooling is puzzling because it is opposite from the expected and simulated global warming trend due to the retreating ice sheets and rising atmospheric greenhouse gases. Our critical reexamination of this contradiction between the reconstructed cooling and the simulated warming points to potentially significant biases in both the seasonality of the proxy reconstruction and the climate sensitivity of current climate models.
Climate science: Uncertain temperature trend
Global mean surface temperatures have not risen much over the past 15 years, despite continuing greenhouse gas emissions. An attempt to explain the warming slow-down with Arctic data gaps is only a small step towards reconciling observed and expected warming.
Current state-of-the-art General Circulation Models (GCMs) do not simulate precipitation well because they do not include the full range of precipitation-forming mechanisms that occur in the real world. It is demonstrated here that the impact of these errors are not trivial – an error of only 1 mm in simulating liquid rainfall is equivalent to the energy required to heat the entire troposphere by 0.3°C. Given that models exhibit differences between the observed and modeled precipitation that often exceed 1 mm day-1, this lost energy is not trivial. Thus, models and their prognostications are largely unreliable
Current climate models generally reflect too little solar radiation over the Southern Ocean, which may be the leading cause of the prevalent sea surface temperature biases in climate models. The authors study the role of clouds on the radiation biases in atmosphere-only simulations of the Cloud Feedback Model Intercomparison Project phase 2 (CFMIP2), as clouds have a leading role in controlling the solar radiation absorbed at those latitudes.
The ‘low’ in the transient temperature versus depth borehole profiles around 120 m seen from deep temperature logs in the Canadian Prairies (southern Alberta–southern Saskatchewan), as well as in some of the European data, has been interpreted to be related to the Little Ice Age (LIA). Data point to the lowest ground surface and subsurface temperatures occurring in the very late eighteenth to nineteenth centuries. Inversion of these logs shows that surface temperature lows were followed by a recent warming period. Further, the synthetic profiles [climate models] built on the basis of [simulated] solar forcing history, stretching as far back as the beginning of the seventeenth century, suggest that the LIA signatures interpreted from the inversion of the borehole temperature logs would be difficult to be explained by known published models of past solar irradiation despite large range of assumed sensitivities for the couplings assumed, and that further [solar] forcing needs to be considered.
The first decade of the 21st century was characterized by a hiatus in global surface warming.
Since the start of the 21st century, the surface global mean temperature has not risen at the same rate as the top-of-atmosphere radiative energy input or greenhouse gas emissions, provoking scientific and social interest in determining the causes of this apparent discrepancy. Multidecadal natural variability is the most commonly proposed cause for the present hiatus period. Here, we analyze the HadCRUT4 surface temperature database with spectral techniques to separate a multidecadal oscillation (MDV) from a secular trend (ST). Both signals combined account for nearly 88% of the total variability of the temperature series showing the main acceleration/deceleration periods already described elsewhere. Three stalling periods with very little warming could be found within the series, from 1878 to 1907, from 1945 to 1969 and from 2001 to the end of the series, all of them coincided with a cooling phase of the MDV. Henceforth, MDV seems to be the main cause of the different hiatus periods shown by the global surface temperature records.
The response of the Southern Ocean and sea ice to ozone depletion is currently a matter of debate. … [T]he issue is reconciling the observed expansion of Antarctic sea-ice extent during the satellite era with robust modelling evidence that the ice should melt as a result of stratospheric ozone depletion (and increases in GHGs).
Regression based statistical models that use air temperature as the predictor of stream temperatures are particularly popular (Kothandaraman 1972, Mohseni et al 1998, Erickson and Stefan 2000, Bogan et al 2003). These models have been used extensively in the United States for projecting future stream temperatures, with estimated increases ranging between 1° and 9 °C by the year 2050 (e.g., Cooter and Cooter 1990, Stefan and Sinokrot 1993, Mohseni et al 2003, Mantua et al 2010). Such changes in stream temperature would have dramatic implications for stream ecosystems (Magnuson et al 1979, Vannote and Sweeney 1980, McCullough et al 2009), particularly cold-water species (Heino et al 2009, Beechie et al 2012).
[W]e examined the performance of two widely used linear and nonlinear regression models that predict stream temperatures based on air temperatures. We evaluated model performance and temporal stability of model parameters in a suite of regulated and unregulated streams with 11–44 years of stream temperature data. Although such models may have validity when predicting stream temperatures within the span of time that corresponds to the data used to develop them, model predictions did not transfer well to other time periods. Validation of model predictions of most recent stream temperatures, based on air temperature–stream temperature relationships from previous time periods often showed poor performance when compared with observed stream temperatures. Overall, model predictions were less robust in regulated streams and they frequently failed in detecting the coldest and warmest temperatures within all sites. In many cases, the magnitude of errors in these predictions falls within a range that equals or exceeds the magnitude of future projections of climate-related changes in stream temperatures reported for the region we studied (between 0.5 and 3.0 °C by 2080). The limited ability of regression based statistical models to accurately project stream temperatures over time likely stems from the fact that underlying processes at play, namely the heat budgets of air and water, are distinctive in each medium and vary among localities and through time.
Recent drought in 1993–2008 was still within the frame of natural climate variability based on the 306 yr PDSI reconstruction. The dry and wet phases of Lingkong Mountain were in accordance with changes in the summer Asian-Pacific oscillation and sunspot numbers, they also showed strong similarity to other tree-ring based moisture indexes in large areas in and around the CLP, indicating the moisture variability in the CLP [Chinese Loess Plateau] was almost synchronous and closely related with large-scale land–ocean–atmospheric circulation and solar activity.
GIDMaPS climate data records can be used to assess the fraction of global land areas under D0 to D4 drought severity levels as displayed in Figure 5 [below link]. The figure highlights a substantial increase in severe to exceptional drought in the late nineties as discussed in previous studies. The figure indicates that in the peak time, around 20% of global land areas were in severe to exceptional drought, a record drought the likes of which has not been experienced since.
[Figure 5 from the paper showing no identifiable drought intensity trends since the early 1980s]
Anthropogenic climate change is expected to increase the frequency of drought events in the earth’s subtropical regions. However, the climate dynamics of these regions are not fully understood and debate surrounds how external forcing factors such as solar and volcanic forcing influence long-term rainfall patterns in the subtropics. Here, we present the first high-resolution reconstruction of Caribbean drought events over the last millennium based on analyses of sediment geochemical data from a continuous high-resolution coastal lake-sediment record in Jamaica. The record suggests extended episodes of drought occurred during the so-called Little Ice Age (1400–1850 CE), which were associated with El-Niño-like conditions in the eastern equatorial Pacific Ocean and controlled by low natural radiative forcing. Comparison of the Jamaican drought record with previously published palaeoclimatic archives from within the circum-Caribbean region suggests that dry conditions were associated with the southward migration of the Hadley Cell, a stronger North Atlantic High and the concomitant intensification of the north-east trade winds and the Caribbean Low Level Jet. We conclude that pre-industrial climatic change in the region was probably controlled by solar forcing and modulated by the combined influence of El Niño Southern Oscillation and the North Atlantic Oscillation.
The causes of the Texas–northern Mexico drought during 2010–11 are shown, using observations, reanalyses, and model simulations, to arise from a combination of ocean forcing and internal [natural] atmospheric variability. The drought began in fall 2010 and winter 2010/11 as a La Niña event developed in the tropical Pacific Ocean. Climate models forced by observed sea surface temperatures (SSTs) produced dry conditions in fall 2010 through spring 2011 associated with transient eddy moisture flux divergence related to a northward shift of the Pacific–North American storm track, typical of La Niña events. In contrast the observed drought was not associated with such a clear shift of the transient eddy fields and instead was significantly influenced by internal atmospheric variability including the negative North Atlantic Oscillation of winter 2010/11, which created mean flow moisture divergence and drying over the southern Plains and southeast United States.
During the summer of 1934, over 70% of western North America experienced extreme drought, placing this summer far outside the normal range of drought variability and making 1934 the single worst drought year of the last millennium. Despite a moderate La Niña, contributions from sea surface temperature forcing were small, suggesting that the anomalous 1934 drought was primarily a consequence of atmospheric variability, possibly amplified by dust forcing that intensified and spread the drought across nearly all of western North America.
CO2 Greening the Earth, Crop Growth (2)
Elevated CO2 further lengthens growing season under warming conditions Our results suggest that a longer growing season, especially in years or biomes where water is a limiting factor, is not due to warming alone, but also to higher atmospheric CO2 concentrations that extend the active period of plant annual life cycles.
http://link.springer.com/article/10.1007%2Fs00704-014-1093-3 Corn yields could increase threefold (measured by method 1) or twofold (method 2) as long-term temperature increased per degree centigrade. And agriculture in northeastern China has benefitted from climate warming.
Tropical Cyclones/Hurricanes (9)
Australian tropical cyclone activity lower than at any time over the past 550–1,500 years
The assessment of changes in tropical cyclone activity within the context of anthropogenically influenced climate change has been limited by the short temporal resolution of the instrumental tropical cyclone record (less than 50 years). Furthermore, controversy exists regarding the robustness of the observational record, especially before 1990. Here we show, on the basis of a new tropical cyclone activity index (CAI), that the present low levels of storm activity on the mid west and northeast coasts of Australia are unprecedented over the past 550 to 1,500 years.
In 1995 an abrupt shift in the late-season (October–December) typhoon activity over the western North Pacific (WNP) is detected by a Bayesian changepoint analysis. Interestingly, a similar change also occurs in the late-season sea surface temperature series over the western Pacific, eastern North Pacific, and portions of the Indian Ocean. All of the counts, lifespans, and accumulated cyclone energy of the late-season typhoons during the 1995–2011 epoch decreased significantly, compared with typhoons that occurred during the 1979–94 epoch. … The ensemble simulations suggest that the recent change to a La Niña–like state induces an unfavorable dynamic condition for typhoon genesis over the southeastern WNP. Warming in the Indian Ocean, however, contributes insignificantly to the circulation anomaly related to typhoon genesis over the southeastern WNP. The frequency of typhoon occurrence reveals a basinwide decrease over the WNP in the recent epoch, except for a small increase near Taiwan.
It is a community wide belief that the Atlantic Multi-decadal Oscillation (AMO) and the Accumulated Cyclone Energy (ACE) are strongly positively correlated and in lock-step for the characterization of a tropical cyclone (TC)—hurricane season; including how many named TCs will form and how many will become hurricanes and major hurricanes. In this paper, we decompose the AMO and ACE time series into their internal modes of variability using the Hilbert-Huang Transform and the Ensemble Empirical Modal Decomposition (EEMD), and look into the relationships that exist between the individual corresponding modes of the AMO and the ACE. We then evaluate the degrees of frequency domain correlations between the internal modes of variability of the AMO and the ACE across the entire record length time series. The 2013 North Atlantic Hurricane Season, which had been predicted to be “above normal”, with an ACE estimated to be between 122 and 138 by the National Oceanic & Atmospheric Administration (NOAA), turned out to be one of the quietest on record. The actual 2013 observed ACE was only 33 (unit: 104 kn2) or 29% of the 65 year (1948-2012) average of 103 (with a median of 89.5) and is the 5th lowest value since 1950.
There is no debate that hurricane activity in the North Atlantic has increased substantially since the relatively quiescent period of the 1970s and 1980s, but there is still uncertainty in the dominant cause of the increase. Increases in anthropogenic greenhouse gases (aGHG) have contributed to the observed increase in tropical sea surface temperatures (SST) over the past century, while shorter-term decadal variability in regions where hurricanes form and track is generally dominated by 1) internal variability, 2) natural factors such as volcanic eruptions and mineral aerosol variability, and 3) changes in anthropogenic aerosols. Direct SST warming from globally well-mixed aGHG is understood to have a much smaller effect on hurricane formation and intensification compared to the effect of regional warming due to changes in the three factors noted above.
Previous observational studies show a strong association between ENSO and Atlantic TC [tropical cyclone] activity, as well as distinctions during eastern Pacific (EP) and central Pacific (CP) El Niño events. The analysis of track density and TC origin indicates that each model has different mean biases. Overall, the GCMs simulate the variability of Atlantic TCs well with weaker activity during EP El Niño and stronger activity during La Niña. For CP El Niño, there is a slight increase in the number of TCs as compared with EP El Niño. However, the spatial distribution of track density and TC origin is less consistent among the models. Particularly, there is no indication of increasing TC activity over the U.S. southeast coastal region during CP El Niño as in observations. The difference between the models and observations is likely due to the bias of the models in response to the shift of tropical heating associated with CP El Niño, as well as the model bias in the mean circulation.
Atlantic tropical cyclone (TC) activity is influenced by interannual tropical Pacific sea surface temperature (SST) variability characterized by the El Niño–Southern Oscillation (ENSO), as well as interannual-to-decadal variability in the interhemispheric gradient in tropical Atlantic SST characterized by the Atlantic meridional mode (AMM). Individually, the negative AMM phase (cool northern and warm southern tropical Atlantic SST anomalies) and El Niño each inhibit Atlantic TCs, and vice versa.
Trend in North Atlantic tropical cyclone frequency is subject to uncertainties related mainly to observational deficiencies. These uncertainties make assessments of anthropogenic effects on present and future trends problematic. Here we document that, contrary to received opinion, ship numbers actually peaked in the mid-nineteenth century and reached a minimum in the early twentieth century. The greater opportunities for ship encounters with tropical cyclones is demonstrated in re-analysis of Eastern Atlantic tropical cyclones from 1851–1898. Our results suggest that nineteenth century [tropical cyclone] frequency is comparable to that for the same area during the entire satellite era from 1965–2012.
We investigated composites of sea surface temperature (SST), wind shear (WS) at 850−200 hPa, and zonal winds at 925 hPa during July−September of the hurricane season to determine interannual and decadal differences between weak (categories 1 to 3, HUR1−3) and intense (categories 4 to 5, HUR4−5) hurricanes in the main development region (MDR) of the Eastern Tropical Pacific (EPAC) during 1970−2010. SST in the MDR showed a statistically significant increase of 0.57°C over the whole period, but the frequency of HUR4−5 did not show a significant trend, while the frequency of HUR1−5 significantly decreased (−0.95% yr−1). This trend is linked to active and in active hurricane periods which are negatively associated with the Atlantic Multidecadal Oscillation and positively with the Pacific Decadal Oscillation (PDO). The frequency of HUR4−5 also shows a significant positive relationship with PDO and El Niño−Southern Oscillation events
The 30–60-day Madden–Julian oscillation (MJO) has been documented in previous research to impact tropical cyclone (TC) activity for various tropical cyclone basins around the globe. The MJO modulates large-scale convective activity throughout the tropics, and concomitantly modulates other fields known to impact tropical cyclone activity such as vertical wind shear, midlevel moisture, vertical motion, and sea level pressure. The Atlantic basin typically shows the smallest modulations in most large-scale fields of any tropical cyclone basins; however, it still experiences significant modulations in tropical cyclone activity. The convectively enhanced phases of the MJO and the phases immediately following them are typically associated with above-average tropical cyclone frequency for each of the global TC basins, while the convectively suppressed phases of the MJO are typically associated with below-average tropical cyclone frequency. The number of rapid intensification periods are also shown to increase when the convectively enhanced phase of the MJO is impacting a particular tropical cyclone basin.
Lower Bound Climate Sensitivity (2)
[A]dding the internal radiative forcing from ENSO in Case III (Fig. 5c) leads to only small adjustments to the model 0-50 m layer temperatures, but a rather large increase in the feedback parameter, λ = 2.8 W m−2 K−1 , corresponding to a climate sensitivity of 1.3°C. … [T]he relatively small differences in the ocean warming profile for the three modeled cases in Fig. 6 – despite a 50% range in assumed climate sensitivity – suggest that the levels of ocean warming observed since the 1950s might not provide a very strong constraint on our estimates of climate sensitivity. The uncertainty in the rates of ocean mixing and the exceedingly small changes in deep ocean temperature contribute to this difficulty in diagnosing the sensitivity of the climate system.
Equilibrium climate sensitivity (ECS) is constrained based on observed near-surface temperature change, changes in ocean heat content (OHC) and detailed radiative forcing (RF) time series from pre-industrial times to 2010 for all main anthropogenic and natural forcing mechanism. The RF time series are linked to the observations of OHC and temperature change through an energy balance model (EBM) and a stochastic model, using a Bayesian approach to estimate the ECS and other unknown parameters from the data. For the net anthropogenic RF the posterior mean in 2010 is 2.0 Wm−2, with a 90% credible interval (C.I.) of 1.3 to 2.8 Wm−2, excluding present-day total aerosol effects (direct + indirect) stronger than −1.7 Wm−2. The posterior mean of the ECS is 1.8 °C, with 90% C.I. ranging from 0.9 to 3.2 °C, which is tighter than most previously published estimates