Skeptic Papers 2019 (2)

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Solar Influence On Climate

Scafetta and Willson, 2019     The consistent downward trending of the PMOD TSI composite is negatively correlated with the global mean temperature anomaly during 1980–2000. This has been viewed with favor by those supporting the COanthropogenic global warming (CAGW) hypothesis since it would minimize TSI variation as a competitive climate change driver to CO2, the featured driver of the hypothesis during the period (cf.: [IPCC, 2013, Lockwood and Fröhlich, 2008]). .. Our summary conclusion is that the objective evidence produced by all of the independent TSI composites [3,5, 6, 9] agrees better with the cycle-by-cycle trending of the original ACRIM science team’s composite TSI that shows an increasing trend from 1980 to 2000 and a decreasing trend thereafter. The continuously downward trending of the PMOD composite and TSI proxy models is contraindicated. … PMOD’s modifications of the published ACRIM and ERB TSI records are questionable because they are based on conforming satellite observational data to proxy model predictions. … ACRIM shows a 0.46 W/m2 increase between 1986 and 1996 followed by a decrease of 0.30 W/m2 between 1996 and 2009. PMOD shows a continuous, increasing downward trend with a 1986 to 1996 decrease of 0.05 W/m2 followed by a decrease of 0.14 W/m2 between 1996 and 2009. The RMIB composite agrees qualitatively with the ACRIM trend by increasing between the 1986 and 1996 minima and decreasing slightly between 1996 and 2009. … ACRIM composite trending is well correlated with the record of global mean temperature anomaly over the entire range of satellite observations (1980–2018) [Scafetta. 2009]. The climate warming hiatus observed since 2000 is inconsistent with CO2 anthropogenic global warming (CAGW) climate models [Scafetta, 2013, Scafetta, 2017]. This points to a significant percentage of the observed 1980–2000 warming being driven by TSI variation [Scafetta, 2009, Willson, 2014, Scafetta. 2009]. A number of other studies have pointed out that climate change and TSI variability are strongly correlated throughout the Holocene including the recent decades (e.g., Scafetta, 2009,  Scafetta and Willson, 2014, Scafetta, 2013Kerr, 2001, Bond et al., 2001, Kirkby, 2007, Shaviv, 2008, Shapiro et al., 2011, Soon and Legates, 2013, Steinhilber et al., 2012, Soon et al., 2014). .. The global surface temperature of the Earth increased from 1970 to 2000 and remained nearly stable from 2000 and 2018. This pattern is not reproduced by CO2 AGW climate models but correlates with a TSI evolution with the trending characteristics of the ACRIM TSI composite as explained in Scafetta [6,12, 27] and Willson [7].

Jiang et al., 2019      In this study, ring-width chronology of Picea jezoensis var. microsperma from the Changbai Mountain (CBM) area, Northeast China, was constructed. …  The reconstructed temperature series corresponded to the historical disaster records of extreme climatic events (e.g., drought and flood disasters) in this area. … It is widely believed that the climate will get colder in periods of less solar activity (e.g., the “Little Ice Age” during AD 1450 and 1850), while in a period of intense solar activity, the climate will become warmer (e.g., the warm period of the Middle Ages during AD 1000 and 1400). … [M]ulti-taper method spectral analysis indicated the existence of significant periodicities in the reconstructed series. The significant spatial correlations between the reconstructed temperature series and the El Niño–Southern Oscillation (ENSO), solar activity, and Pacific Decadal Oscillation (PDO) suggested that the temperature in the CBM area indicated both local-regional climate signals and global-scale climate changes. … The 11-year smoothing average of the reconstructed Tmax6–7 series was used to reveal low-frequency information and to show temperature variability in this area. After smoothing with an 11-year moving average, cold periods occurred in 1899–1913 (average value was 21.41 °C), 1955–1970 (21.49 °C), and 1975–1989 (20.97 °C), while warm periods occurred in 1881–1888 (23.93 °C). Furthermore, there are six obvious processes of Tmax6–7 increasing in 1781–1791 (from 22.76 °C to 23.54 °C), 1800–1809 (from 22.72 °C to 23.44 °C), 1835–1845 (from 22.66 °C to 23.76 °C), 1900–1919 (from 21.47 °C to 22.30 °C), 1931–1942 (from 21.36 °C to 22.04 °C), and 1983–2004 (from 20.49 °C to 22.99 °C), and five obvious processes of Tmax6–7 decreasing in 1790–1800 (from 21.89 °C to 22.98 °C), 1810–1835 (from 23.40 °C to 22.66 °C), 1880–1901 (from 23.83 °C to 21.25 °C), 1917–1931 (from 22.36 °C to 21.36 °C), and 1970–1983 (from 21.75 °C to 20.49 °C). In addition, the temperatures during 1780–1890 were much warmer (average value was 23.35 °C) than the temperatures during 1900–2004 (average value was 21.65 °C).

Moreno et al., 2019     Spectral and wavelet transform coherence analyses were used to detect solar footprints on foraminiferal and climate-related time series. A main significant quasi-periodicity was identified within the range of the secular Gleissberg cycle of solar activity modulating the annual NAO and regional spring-summer (simulated) temperatures after AD 1700. This stronger solar-climate coupling may be related to the known upward secular trend in the total solar irradiance after the Maunder Minimum.
Zhao et al., 2019     TSI provides nearly 99.96% of the energy driving Earth climate and its 0.15% variation has a great influence (Kren 2015). Moreover, not only does TSI vary by about 0.01%, caused by the several-minutes-long continuous change from the solar convection zone to the photosphere, it also varies by about 0.3% over 300 years (Eddy 1976). Besides TSI, solar wind is another solar activity, which consists of three types based on the different velocity, extremely high-velocity (v≥725 km/s), high-velocity (450≤v<725 km/s) and low-velocity (v<450 km/s) wind. While TSI is an important observable factor in solar activity variation, a lot of weather and climate models attempt to attribute it as a physically important factor when trying to understand whether and how the Sun has an impact on the Earth’s weather and climate (Scafetta 2010; Coddington et al. 2016). Beyond the widely known quasi 11-year and century periods, Mendoza (2005) concluded that the TSI fluctuations on the 5 min range are due to solar oscillations (Fröhlich et al. 1997; Wolff and Hickey 1987), while few days to weeks are dominated by sunspots (Chapman 1987), and faculae can enhance the total flux by 0.08% (Hudson et al. 1982). Apart from the intrinsic longand short-term variations of TSI, the changes of the Earth’s orbital parameter and albedo cause the variations of the solar electromagnetic radiation that arrives at the Earth (Mendoza 2005). The radiation, especially in the UV bands influenced by the short but strong solar activity (e.g., flare, coronal mass ejection), affects the temperature variation that plays a key role in climate change (Smith et al. 1990).
Li et al., 2019      The result obtained by analyzing that quasiperiodicity shows that the main periods of tree ring width and the sunspot number in the same period are basically consistent, and tree ring width has other cycles. This shows that sunspot activity is an important factor affecting tree ring growth, and tree ring width is influenced by other external environments. … The influence of solar activity on climate has attracted much attention as early as the seventeenth century. Solar activity is an important controlling factor of the earth’s climate. It plays a leading role in the earth’s climate change [1]. Many research studies [2–4] have shown that solar activity is closely related to natural environment changes such as temperature and various dust storms, floods, and droughts.
Zherebtsov et al., 2019     We address the solar activity effect on the changes in the temperature of the atmosphere and of the World Ocean. … We revealed the regions, where long-term SST changes are determined mainly by SA [solar activity] variations. … Comparing variations in climate and solar activity reveals great similarity in their behavior on large time scales. In particular, there are reasonable grounds to believe that the periods of cooling and warming (at least, in the previous millennium) were precisely related to the solar activity variations. Over recent 1000 years, climate has undergone the changes that corresponded to the solar activity variations: warming was recorded in the 12–13th centuries, when solar activity was high (“Medieval Climatic Optimum”), and two temperature drops in the Little Ice Age (in the 16–17th centuries) corresponded to long periods of low solar activity (Dalton and Maunder Minima) (Fig. 1). After the Maunder Minimum, solar activity increase has been widely observed. So, the world climate has become warmer during the bulk of this period. … Earlier, the authors (Kirichenko et al., 2014) analyzed the long-term variations in the SST spatial distribution and in geomagnetic activity. As a result, we found a relation between the SST changes and the geomagnetic activity variations. The SST response to geomagnetic effects was established to feature a significant spatial time irregularity and has a regional character. … Based on the complex analysis of the hydro-meteorological observational data and the authors’ model for the solar activity effect on the climate system, we obtained new evidence for the SA [solar activity] effect on the weather-climate characteristics in the troposphere and in the ocean, including the surface air temperature and the ocean surface temperature. … We calculated the temperature vertical profile variations within the troposphere during heliogeophysical disturbances. The troposphere temperature response to individual heliogeophysical disturbances is shown to be accompanied by the temperature field regular change. In the regions of the temperature maximal response to heliogeophysical disturbances in the middle and in the lower troposphere, one observes a significant (up to 15°) temperature increase. … We found the regions, in which long-term variations in the ocean surface temperature are mainly determined by geomagnetic activity variations. Along with this, the wind stress direction variations were revealed to affect the manifestation of the solar-geomagnetic effect on the ocean surface temperature. They lead to a “hiatus” in the relation between the ocean surface temperature and solar activity due to the change in the ocean thermodynamic state because of the vertical mixing increase.
Deininger et al., 2019     A centennial periodicity of the SAMS [South American Monsoon System] (around 210 years) was reported from different sites and is associated with the de Vriess–Suess solar cycle, exhibiting depleted δ18O during  periods of high solar irradiance. It is proposed that this relationship is due to several feedbacks involving amplification of solar forcing by coupled air-sea dynamics, cloud formation and stratospheric warming due to enhanced UV absorption through increased stratospheric ozone concentration. … The proposed mechanism driving the Botuverá δ18O record in southeast Brazil is intensification of the SAMS [South American Monsoon System], as driven by increasing austral summertime insolation, suggesting a progressive increase in precipitation amount throughout the Holocene.The main climate features over the last two millennia in South America were forced by NH warm and cold periods during the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA), respectively. … During the CWP [current warm period], the convective conditions over South America appear to be similar to the MCA [Medieval Climate Anomaly], with warming in the NH leading to a northward positioning of ITCZ and a progressive weakening of the SAMS.

Ball et al., 2019     The solar cycle (SC) stratospheric ozone response is thought to influence surface weather and climate. To understand the chain of processes and ensure climate models adequately represent them, it is important to detect and quantify an accurate SC ozone response from observations. Chemistry climate models (CCMs) and observations display a range of upper stratosphere (1–10 hPa) zonally averaged spatial responses; this and the recommended dataset for comparison remains disputed. Recent data‐merging advancements have led to more robust observational data. Using these data, we show that the observed SC [solar cycle] signal exhibits an upper stratosphere Ushaped spatial structure with lobes emanating from the tropics (5–10 hPa) to high altitudes at midlatitudes (1–3 hPa). We confirm this using two independent CCMs in specified dynamics mode and an idealised timeslice experiment. We recommend the BASICv2 ozone composite to best represent historical upper stratospheric solar variability, and that those based on SBUV alone should not be used.
Kusch et al., 2019     The Holocene climate history of the high-Arctic has largely been driven by the decline in summer insolation (Berger & Loutre 1991; Kaufman et al. 2004) amplified by oceanic and atmospheric feedbacks, most importantly an increased meridional heat and moisture transfer, as well as volcanic forcing (Briner et al. 2016; Kobashi et al. 2017; Lecavalier et al. 2017). Mean summer insolation at 80°N was approximately 50 W m-2 higher during the Early Holocene (Greenlandian) insolation maximum compared to today and resulted in the Early to Middle Holocene thermal maximum (HTM) causing retreat and disappearance of the northern ice sheets except for the Greenland Ice Sheet (Berger & Loutre 1991; Ullman et al. 2015). … Most records, including ice-cores and sedimentary archives, document the HTM between approximately 9 and 5 cal. ka BP with average temperature anomalies of 2.5 to 3.0 °C [higher than today] (Briner et al. 2016) in agreement with climate models (e.g. Renssen et al. 2012).

Yan et al., 2019     We contend that solar activity and the westerlies were the dominant influences on ACA [arid central Asia] hydroclimatic variations during the period of record [the last 160 years]: (1) solar activity dominates regional temperature variations, precipitation/evaporation, and the advance/retreat of glaciers; (2) stronger westerly intensity (corresponding to higher westerly index and higher North Atlantic Oscillation (NAO) index) brings more water vapor from the west to ACA [arid central Asia], and vice versa; and (3) the southerly migration of the westerly jet stream, which is closely related to lower TSI and temperatures, could favor more water vapor transported to ACA areas, and vice versa.
Nitka and Burnecki, 2019     In this paper we analyze the relationship between the sunspot numbers and the average monthly precipitation measured at meteorological stations in the US. The results indicate that there is a significant correlation between the solar activity and the monthly average precipitation data for selected months and time delays.
Huang et al., 2019     [T]hese events are synchronous with periods of weak solar activity, and the spectral analysis demonstrates that the EASM and solar activity share some general cyclicity patterns. We therefore suggest that solar activity is a fundamental driving force for the spatial synchronisation of the EASM [East Asian Summer Monsoon] on centennial timescales across the monsoon region. … The sun-monsoon link can be explained by a direct solar influence on the land–sea thermal contrast that controls the monsoonal precipitation (Liu et al., 2009; Xu et al., 2015). When the land–sea thermal contrast reduces, the subsequent gradual southward migration of the Intertropical Convergence Zone (ITCZ) may lead to reduced transportation of water vapor from the ocean to the continents, thereby causing less rainfall in monsoonal Asia (Dykoski et al., 2005; Fleitmann et al., 2003; Li et al., 2017b). In general, weak solar activity triggers decreased land–sea thermal contrast, and thereafter would result in reductions in the EASM intensity. Alternately, solar output could influence the variability of the EASM indirectly, perhaps amplified by the North Atlantic teleconnection (Wang et al., 2005, 2016).
Liu et al., 2019     Notably, an overall inphase relationship is observed between the hydroclimatic variations and change in solar activity, and the results of spectral analysis suggest the presence of the Eddy (~1080 yr), de Vries (~205 yr) and Gleissberg (~88‐102 yrs) cycles. This indicates a linkage between solar activity and hydroclimatic changes in ACA [arid Central Asia] on centennial‐ to multi‐decadal scales during the Holocene. We suggest that the influence of solar activity on hydroclimatic changes in ACA [arid Central Asia] occurs via its effects on North Atlantic sea surface temperature (SST), North Atlantic Oscillation (NAO), northern highlatitude regional temperatures, and via direct heating. The relationship suggests that solar activity may play an important role in determining future hydroclimatic changes in ACA [arid Central Asia].
Banerji et al., 2019     The present study demonstrates vacillating climate with strengthened ISM [Indian Summer Monsoon] during Roman Warm Period and Medieval Warm Period (2000−950 cal yr BP) as a result of increased solar irradiance interrupted by reduced ISM during Dark Ages of Cold Period (∼1500 cal yr BP). The plausible occurrence of volcanic eruption before the onset of Little Ice Age (500−200 cal yr BP) resulted the southward migration of ITCZ leading to enhanced western disturbances in the study area thereby causing cool and wet climate. The study also emphasis the increased El Nino events with gradual decline in the ISM since LIA. Further, the study underscores a climate warming during last two centuries which corroborated well with the instrumental records. Thus, the present study has implication towards understanding the significant role of volcanic activity and solar variability in controlling the millennia scale climate oscillations with additional feedback mechanisms.
Cho et al., 2019     [T]he EASM [East Asian Summer Monsoon] was weak during the LIA, and the amount of precipitation was lower than in other periods. ENSO is strongly related to sea surface temperature (SST) in the Pacific Ocean (Schwing et al., 2002; Marchitto et al., 2010). This SST is also affected by solar activity. Marchitto et al. (2010) showed that proxy-based SST records based on Mg/Ca ratio correlated with the generation of cosmogenic nuclides 14C and 10Be. Therefore low solar activity is correlated with El Niño-like conditions (Marchitto et al., 2010). Japan has a complicated climate system, but it is one that is closely related to solar insolation. The climate of Japan over the last 1000 years has undergone significant variation. The LIA was in place for about 650 years from 1300–1950 CE (Matthews and Briffa, 2005). Before the LIA, the Medieval Solar Maximum occurred from 1100 CE–1250 (Jirikowic and Damon, 1994). During the LIA, El Niño was strong, and typhoons during El Niño years tended to recurve to the northeast (Wang and Chan, 2002), which may increase the likelihood of typhoons making landfall in Japan (Elsner and Liu, 2003).
Le Mouël et al, 2019     We first apply singular spectrum analysis (SSA) to the international sunspot number (ISSN; 1849‐2015) and the count of polar faculae (PF; 1906‐2006). The SSA method finds 22, 11 and 5.5‐year components as the first eigenvectors of these solar activity proxies. We next apply SSA to the ten Madden‐Julian oscillation (MJO; 1978‐2016) indices. The first, most intense component SSA finds in all MJO indices has either a period of 5.5 or 11 years. The longer‐term modulation of amplitude is on the order of one third of the total variation. The 5.5‐year SSA component 1 of most MJO indices moreover follows the decreasing amplitude of solar cycles. We then apply SSA to climate indices PDO, ENSO, WPO, AAO, AMO, TSA, WHWP, and Brazil and Sahel rainfalls. We find that the first SSA eigenvectors are all combinations of rather pure 11, 5.5 and 3.6‐year pseudo‐cycles. The 5.5‐year component is frequently observed and is particularly important and sharp in the series in which it appears. All these periods have long been attributed to solar activity, and this by itself argues for the existence of a strong link between solar activity and climate. The mechanisms of coupling must be complex and probably nonlinear but they remain to be fully understood (UV radiation, solar wind and galactic cosmic rays being the most promising candidates). We propose as a first step a Kuramoto model of non‐linear coupling that generates phase variations compatible with the observed ones.
Fang et al., 2019    An astronomically forced cooling event during the Middle Ordovician … Onset and termination of a cooling event in the Middle Ordovician were dated. Obliquity forcing dominated this cooling event. 1.2 Myr obliquity modulation cycles controlled the third-order eustatic sequences. Onset and termination of cooling event were controlled by astronomical forcing.
Jia and Liu, 2019     Here, we present well-dated Xray fluorescence scanning records retrieved from a varved sediment core from Lake Kusai. These records show the decadal- to-centennial-scale paleoclimatic variability of the northern Qinghai-Tibetan Plateau over the last 2000 yr. Ca is mainly related to the precipitation of authigenic carbonates and is a proxy for temperature changes. The Ca record of Lake Kusai is well-correlated with the variations and periodicities of solar activity. Therefore, solar output can be suggested as being the predominant forcing mechanism of decadal- to centennial-scale temperature fluctuations over the last 2000 yr.
Jin et al., 2019     For the four-member ensemble averaged solar-only forcing experiment, the summer mean precipitation over northern EA is significantly correlated with the solar forcing (r 5 0.414, n 5 68, p, 0.05) on a decadal time scale during the strong cycle epoch, whereas there is no statistical link between the EASM and solar activity during the weak cycle epoch (r 5 0.002, n 5 24). A strong, 11-yr solar cycle is also shown to excite an anomalous sea surface temperature (SST) pattern that resembles a cool Pacific decadal oscillation (PDO) phase, which has a significant 11-yr periodicity. The associated anomalous North Pacific anticyclone dominates the entire extratropical North Pacific and enhances the southerly monsoon over EA, which results in abundant rainfall over northern EA. We argue that the 11-yr solar cycle affects the EASM decadal variation through excitation of a coupled decadal mode in the Asia–North Pacific region.
Liu et al., 2019      The regional May–July PDSI (PDSI5−7) from the CW-DHM was reconstructed from 1825 to 2013 AD. The ensemble empirical mode decomposition method (EEMD) and multi-taper method (MTM) spectral analyses revealed that the cycles in the reconstructed PDSI5−7 were close to those of the ENSO and solar activity. This suggests that both the ENSO and solar activity have strong influence on the PDSI5−7 [drought] variation in the CW-DHM region. In addition, EEMD also revealed that the Pacific decadal oscillation and the Atlantic multi-decadal oscillation influenced the drought variation in this region. The PDSI5−7 reconstruction showed a long-term declining (dry) trend during the period of the 1950s–2010s. This drying trend was also detected in the PDSI data of other parts of China after the 1950s. We believe that these phenomena may be related to a large extent with the weakening of the East Asian summer monsoon.
Gao et a., 2019     At the centennial scale, the penguin population recorded in core RNL decreased from ~1120–860 yr BP, reached a peak from ~860–630 yr BP, remained at a low level from ~630–320 yr BP, and then increased with large fluctuations during the past ~400 years. These changes are all in-phase with the trend of solar irradiance. At the decadal scale, penguin population minima correspond to solar minima from ~490–400 yr BP (Spörer minimum), ~290–220 yr BP (Maunder minimum), and from ~160–120 yr BP (Dalton minimum; whereas population maxima correspond to solar maxima from ~1030–980 yr BP, ~350–290 yr BP, ~210–160 yr BP, ~120–70 yr BP. The population recorded in core RL exhibited the same changes as in RNL during the last 480 years. The reconstructed krill abundance also corresponds to these trends when data are available. This correspondence demonstrates a food-chain mechanism that is related to solar activity and light availability at the ocean surface, which influence the intensity of photosynthesis and phytoplankton productivity, and thus the abundance of krill and apex predators such as penguins. Our findings highlight the fact that despite the various climatic impacts on penguin populations, their effects on the base of the food chain are usually the direct drive. … In summary, changes in solar irradiance control the energy input to the ecosystem, which influences the phytoplankton biomass in the penguin foraging area; in turn, this leads to changes in krill abundance and thus penguin food availability, which has a significant impact on the development of the penguin population.
Goslin et al., 2019     Here we present a reconstruction of westerly storminess in western Denmark between 4840 and 2300 yrs. cal. B·P. Past-storminess is retrieved from an organic-rich sedimentary succession by combining markers of aeolian sand influx, μ-XRF geochemistry and plant macrofossils. Particular focus is paid to the c. 4840–4350 yrs. cal. B·P. period for which our record is characterized by a pluri-annual resolution. We evidence concurrent pluri-decadal shifts in storminess and humidity regime at our site that we interpret as relocations of the mean westerly storm-track over the North-Atlantic. The signal is dominated by ≈ 90, ≈ 50–80 and ≈ 35-yr periods, evoking possible links with solar activity, the North-Atlantic Oscillation (NAO), the Atlantic Multidecadal oscillation (AMO) and the Atlantic Meridional Overturning Circulation (AMOC) modes of variability, respectively. The ≈ 35-yr periodicity found in our record is especially strong and stationary, suggesting that storminess could have been closely linked with the AMOC over the study period.
Prikryl et al., 2019     Rapid intensification of tropical storms tends to follow arrivals of high-speed solar wind. Convective bursts have been linked to rapid intensification of tropical cyclones. Cases of tropical cyclone intensification closely correlated with the solar wind structure are found to be preceded by atmospheric gravity waves generated by the solar wind magnetosphere-ionosphere-atmosphere coupling process.
Constantine et al., 2019     The records indicate that climate deteriorations around 6400 cal yr BP and 4000 cal yr BP caused rapid vegetation changes in the study area, which were presumably attributable to low sunspot activity and strong El Niño–like conditions, respectively. These two cooling events were likely modulated by different climate mechanisms, as El Niño–Southern Oscillation activity began to strengthen around 5000 cal yr BP. These events may have had a substantial impact on ancient societies in the study area. Combining our results with archaeological findings indicated that climate deterioration led to drastic declines in local populations around 6400 cal yr BP, 4400 cal yr BP, and 4000 cal yr BP. Because of its high population, coastal East Asia (e.g., eastern China, Japan, and Korea) is particularly vulnerable to potential cooling events in the future.
Lucas, 2019     A solar minimum period begins when sunspot activity decreases. Solar cycles can last for periods ranging from as short as seven to eleven years, or as long as 400 years (Popova, et al. 2017). The solar minimum is caused when the sun’s magnetic field weakens, causing a decrease in solar material, called the solar wind. The sun’s magnetic field, known as a magnetic shield, “deflects low-energy cosmic rays” from reaching the Earth (Tomassetti et al. 2017). When solar activity is high, at a solar peak, solar wind is low, with less cosmic radiation reaching the Earth. During the sun’s solar minimum, the magnetic field protecting the Earth is weakened and Earth receives more cosmic radiation. The result for civilizations on Earth is unpredictable swings in the climate appearing “simultaneously with other markers of social change” (Nelson & Khalifa, 2010). … There is climatologic evidence of solar cycle peak and trough in global temperatures as noted in climatic studies of solar isotopes (Usoskin 2008). During solar maximums we would expect to see evidence of the rise of civilizations when the climate is warmer, and evidence of civilization collapse during solar minimums as the climate turns colder and geologic instability follows.
Laurenz et al., 2019     Results show that February precipitation in Central and Western Europe yields the strongest solar response with coefficients reaching up to +0.61. Rainfall in June–July is equally co-driven by solar activity changes, whereby the solar-influenced zone of rainfall shifts from the British Isles towards Eastern Europe during the course of summer. … The literature review demonstrates that most multidecadal studies from Central Europe encountered a negative correlation between solar activity and rainfall, probably because short time lags of a few years are negligible on timescales beyond the 11 year solar Schwabe cycle. Flood frequency typically increases during times of low solar activity associated with NAO- conditions and -more frequent blocking.
Miyake et al., 2019     New quasi-annual beryllium-10 measurements were made with the Dome Fuji ice core from Antarctica over the period in which the 994 cosmic ray event would be expected. We observed an approximately 50% increase in beryllium-10 concentrations, which is consistent with the beryllium-10 increases observed in the Greenland ice cores. This lends support to a solar origin of the 994 event.
Kushnir and Stein, 2019     Medieval Climate in the Eastern Mediterranean: Instability and Evidence of Solar Forcing … The Nile summer flood levels were particularly low during the 10th and 11th centuries, as is also recorded in a large number of historical chronicles that described a large cluster of droughts that led to dire human strife associated with famine, pestilence and conflict. During that time droughts and cold spells also affected the northeastern Middle East, in Persia and Mesopotamia. Seeking an explanation for the pronounced aridity and human consequences across the entire EM, we note that the 10th–11th century events coincide with the medieval Oort Grand Solar Minimum, which came at the height of an interval of relatively high solar irradiance. Bringing together other tropical and Northern Hemisphere paleoclimatic evidence, we argue for the role of long-term variations in solar irradiance in shaping the early MCA in the EM and highlight their relevance to the present and near-term future.

Solar Magnetic-Cosmic Rays-Clouds-Influence

Audu and Okeke, 2019     Sunspot number, aa index, galactic cosmic rays (GCRs), rainfall and maximum temperature data were used in this study. The time period under investigation in this study spanned for 63 years (1950–2012). Spearman’s rank correlation technique was employed in analyzing the data. Results reveal that sunspot number and aa index varied in the opposite direction with GCRs based on the 11-year solar cycle. This inverse relationship was confirmed from the correlation analysis. This depicts that solar and geomagnetic activities modulate cosmic rays penetrating into the Earth’s atmosphere. … [T]he variations of cloud covers with rainfall and temperature show that changes in cloud covers are associated with changes in rainfall and temperature. This study has given useful information on the possible links by which solar activity could influence climate change. … According to Kitaba et al. [22], geomagnetic activity influenced the global climate through the modulation of cosmic rays flux. Palamara [19], found out that solar-modulated geomagnetic activity is an important forcing mechanism for the recent climate change. … The pathway proposed for solar—climate interaction in this study is: solar activity/geomagnetic activity → GCRs → cloud cover → climatic parameters.
Svensmark, 2019      These results are also supported by observations. On rare occasions, ‘explosions’ on the Sun, known as ‘coronal mass ejections’, result in a plasma cloud that passes the Earth, causing a sudden decrease in the cosmic ray flux that lasts for a week or two. Such events are called ‘Forbush decreases’, and are ideal to test the link between cosmic rays and clouds. Finding the strongest Forbush decreases and using three independent cloud satellite datasets and one dataset for aerosols, a clear response in clouds and aerosols to Forbush decreases is seen. Figure 14 shows the sum of the five strongest Forbush decreases (red curves) together with various signals observed in clouds (blue curves) in the days around the minimum in cosmic rays. The difference in the position of minima of the two curves is due to the time it takes aerosols to grow into cloud condensation nuclei. These results suggest that the whole chain – from solar activity, to cosmic rays, to aerosols (CCN), to clouds – is active in the Earth’s atmosphere. Moreover, they indicate that the cosmic ray–cloud link is capable of explaining the magnitude of around 1 W/m2 of the observed forcing over the solar cycle.

Isozaki, 2019     As the G-LB and end-Ordovician extinctions share multiple similar episodes including the appearance of global cooling (Category 2), the same cause and processes were likely responsible for the biodiversity drop. In addition to the most prevalent scenario of mantle plume-generated large igneous provinces (LIPs) (Category 3) for the end-Permian extinction, an emerging perspective of cosmoclimatology is introduced with respect to astrobiology. Galactic cosmic radiation (GCR) and solar/terrestrial responses in magnetism (Category 4) could have had a profound impact on the Earth’s climate, in particular on extensive cloud coverage (irradiance shutdown). The starburst events detected in the Milky Way Galaxy apparently coincide in timing with the cooling-associated major extinctions of the Phanerozoic and also with the Proterozoic snowball Earth episodes. As an ultimate cause (Category 4) for major extinction, the episodic increase in GCR-dust flux from the source (dark clouds derived from starburst) against the geomagnetic shield likely determined the major climate changes, particularly global cooling in the past. The study of mass extinctions on Earth is entering a new stage with a new astrobiological perspective.

Zhang et al., 2019     Studies of solar activity and cosmic radiation indicate that solar activity is the main factor driving climate change on decadal-to centennial scales (Stuiver and Braziunas, 1993; Xu et al., 2014; Yu and Ito, 1999; Zhao et al., 2010). In addition, solar activity is well correlated with global surface temperature (Bond et al., 2001; Usoskin et al., 2003). Changes in the production rates of two common cosmic radionuclides (∆14C and 10Be), which are preserved in ice cores and tree rings, suggest that periodic fluctuations in solar activity on decadal-to-centennial scales directly affect the cosmic ray flux (Abreu et al., 2013; Masarik and Beer, 1999; Steinhilber et al., 2012). Kirkby (2007) summarized evidence for a close relationship between temperature change and solar activity during the last millennium, finding that cosmic radiation flux was weak and solar activity was strong during the MWP; whereas, the opposite conditions occurred during the LIA. Therefore, the cosmic ray flux can be regarded as a proxy for solar activity and that it can be used to assess the relationship between climate change and solar activity. … Several notable cold periods, with lower Quercus frequencies, occurred at approximately 1200 AD, 1410 AD, 1580 AD, 1770 AD and 1870 AD. These centennial-scale cold periods basically correspond to major minima in solar activity, suggesting that variations in solar activity may have been an important driver of climate and vegetation change in the study area during the last millennium.

Misios et al., 2019     Influences of the 11-y solar cycle (SC) on climate have been speculated, but here we provide robust evidence that the SC affects decadal variability in the tropical Pacific. By analyzing independent observations, we demonstrate a slowdown of the Pacific Walker Circulation (PWC) at SC maximum. We find a muted hydrological cycle at solar maximum that weakens the PWC and this is amplified by a Bjerknes feedback. Given that a similar muted hydrological cycle has been simulated under increased greenhouse gas forcing, our results strengthen confidence in model predictions of a weakened PWC in a warmer climate. The results also suggest that SC forcing is a source of skill for decadal predictions in the Indo-Pacific region.
Ning et al., 2019     The results show that internal climate variability within the coupled climate system plays an essential role in triggering megadroughts, while different external forcings may contribute to persistence and modify the anomaly patterns of megadroughts. … For the mechanisms behind megadroughts over eastern China, circulation anomalies, e.g., Western Pacific subtropical high (WPSH) and Eastern Asia summer monsoon (EASM), are the direct causes of megadroughts, while external forcing, e.g., solar radiation and volcanic eruptions, may influence the regional climate by changing large-scale circulation patterns [33–36]. For example, Shen et al. [37] found that several exceptional droughts over eastern China during the last 500 years may have been triggered by large volcanic eruptions and amplified by both volcanic eruptions and El Niño events. Through model simulations, Peng et al. [38] indicated that solar activity may be the primary driver in the occurrence of several persistent droughts over eastern China, and the influences occurred through EASM weakening.

Surface Solar Radiation Climate Influence

Skalik and Skalikova, 2019     The global horizontal radiation has been measured for a high number of years at all of these stations. The values show a tendency of increased annual global radiation, most likely due to decreased pollution of the atmosphere, increased duration of periods without clouds and/or combination of both these effects. Twenty years of measurements from a climate station in Lyngby, Denmark show that the global radiation increase is almost 3.5 kWh/m2 per year, corresponding to a growth of 7 % for the last 20 years. The global radiation variation between the least sunny year to the sunniest year is 22%. Twenty-nine years of measuring of global radiation from twelve radiation stations across Sweden shows an increase of 3.1 kWh/m2 per year. The increase is 87 kWh/m2, corresponding to 9 % of global radiation growth during the last 29 years. The annual global radiation varies between 838 kWh/m2/year in 1998 and 1004 kWh/m2/year in 2002 with an average radiation of 932 kWh/m2/year, corresponding to a radiation variation from the least sunny year to the sunniest year of 20 %.
Poprovsky, 2019     The results of analysis of climatic series of global and regional cloudiness for 1983–2009. Data were obtained in the framework of the international satellite project ISCCP. The technology of statistical time series analysis including smoothing algorithm and wavelet analysis is described. Both methods are intended for the analysis of non-stationary series. The results of the analysis show that both global and regional cloudiness show a decrease of 2–6%. The greatest decrease is observed in the tropics and over the oceans. Over land, the decrease is minimal. The correlation coefficient between the global cloud series on the one hand and the global air and ocean surface temperature series on the other hand reaches values (–0.84) — (–0.86). This means that the inflow of solar radiation in the tropics is increasing faster than the global average, and this growth is more than 1 W/m2. Since the tropics are dominated by water areas, this fact suggests that the increasing influx of solar radiation primarily entails an increase in the temperature of the ocean surface (TPO). Not surprisingly, the cloud cover values themselves and their temporal trends are close to global characteristics. Thus, changes in cloud cover over three decades during global warming can explain not only the linear trend of global temperature, but also some interannual variability. … However, the influence of clouds on climate change cannot be ignored because of the significant contribution of this climate-forming parameter and should be studied more closely to improve climate forecasts.

ENSO, NAO, AMO, PDO Climate Influence

Toth and Aronson, 2019     In summary, elevated water temperatures and high irradiance (resulting from low cloud cover) associated with the strong El Niño events in 1982–1983 and 1997–1998 in Pacific Panama caused widespread coral bleaching, which was associated with mass coral mortality in the earlier event (Glynn et al., 2001). La Niña is also problematic for corals in Pacific Panama. Lowered sea level in the TEP during La Niña events causes more frequent coral mortality associated with subaerial exposure (Eakin and Glynn, 1996; Toth et al., 2017). In addition, La Niña is associated with elevated rainfall and enhanced upwelling in Pacific Panama. Elevated rainfall increases turbidity, and enhanced upwelling reduces water temperatures, decreases pH, and increases nutrient levels. All of these changes act to suppress coral growth (Glynn, 1976). … We conclude that ENSO was likely the primary driver of the collapse of coral reefs in Pacific Panama and, perhaps, other locations around the tropical Pacific at ∼ 4.2 ka.
Schmidt et al., 2019     This study examines the climatic drivers of ice-off dates for lakes and rivers across the Northern Hemisphere. Most lakes and rivers have trended toward earlier ice-off dates over the last century, as would be expected from long-term climate change. However, we also identify modes of climate variability that significantly impact the short-term behavior of ice-off time series. In particular, the North Atlantic Oscillation (NAO), Pacific-North American Pattern (PNA), and to a lesser degree the El Niño-Southern Oscillation (ENSO) explain a substantial fraction of the interannual variance in melt dates, while the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO) generally do not. Furthermore, the spatial pattern of the early or late ice-off dates associated with the NAO, PNA, and ENSO matches a priori expectations due to the known surface temperature patterns associated with these oscillations. In all regions, the strongest correlation to ice-off is with one of the high-frequency modes—the NAO or PNA, suggesting that short-term weather variations play a stronger role than lower-frequency climate variability (ENSO, PDO, AMO) in driving ice-off.
Gao et al., 2019     The frequency and intensity of extreme high temperature (EHT) in the Northern Hemisphere exhibit remarkable low-frequency (LF) variations (longer than 10 years) in summer during 1951–2017. Five hotspots featuring large LF variations in EHT were identified, including western North America–Mexico, eastern Siberia, Europe, central Asia, and the Mongolian Plateau. The probability density functions show that the higher EHT occurrences over these hotspots in recent decades is consistent with the shifted average and increased variances in daily mean temperature. The common features of the LF variation in EHT frequency over all domains are the remarkable increasing trends and evident decadal to multidecadal variations. The component of decadal to multidecadal variations is the main contribution to the LF variations of temperature in the last century. Further analysis shows that the coherent variability of decadal to multidecadal temperature variations over western North America–Mexico, eastern Siberia, Europe, and the Mongolian Plateau are the footprints of a dominant natural internal signal: the Atlantic multidecadal oscillation. It contributes to the variations in temperature over these hotspots via barotropic circumglobal teleconnection, which imposes striking anomalous pressure over these regions. This study implies that natural internal variability plays an important role in making hotspots more vulnerable to EHT.
Chafik et al., 2019     After 2005, we observe a gradual transition from a weak to a strong subpolar gyre, which is related to the cooling and freshening trend of the SPNA.[Subpolar North Atlantic]. The anomalously low sea level during the past few winters (2014–2016) can be attributed to the exceptionally strong North Atlantic Oscillation and hence a return to the conditions seen during the early 1990s. We estimate the regional SPNA trend during the WP and CP to be about 3.9±1.5mm/yr and −7.1±1.3mm/yr, respectively. … Oceanic climate variability in the North Atlantic is known to be dominated by decadal-to-multidecadal fluctuations that have profound regional and global climate impacts. Recent observational evidence shows that the strength of the Atlantic Meridional Overturning Circulation or AMOC, i.e. the flow of warm surface waters polewards and the return of cold deep waters equatorwards, is indeed the major factor regulating the warm and cold decades of the North Atlantic as has long been hypothesized. This decadal-scale AMOC variability can have substantial influence on dynamical sea-level change, especially on regional scale, as a result of variable amount of mass, heat and freshwater redistributed by ocean currents.

Hahn et al., 2019     Since the 2000s, a change in the atmospheric circulation over the North Atlantic resulting in more frequent blocking events has favoured warmer and sunnier weather conditions over the Greenland Ice Sheet (GrIS) in summer, enhancing the melt increase. This circulation change is not represented by general circulation models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5), which do not predict any circulation change for the next century over the North Atlantic. … In recent decades, the most extreme melt seasons exhibited significant high-pressure blocking anomalies over Greenland associated with positive GBI values and the negative phase of the NAO (Fettweis, Hanna, et al., 2013; Tedesco et al., 2016; Figure 1), with significant increases in summer Greenland blocking since 1981 (Hanna et al., 2016, Hanna, Hall, et al., 2018). These prolonged atmospheric blocking episodes may promote melt via northward advection of warm air over west Greenland (Fettweis et al., 2011), adiabatic warming of sinking air associated with anticyclonic circulation anomalies (Ding et al., 2017), or radiative impacts of cloud cover changes resulting from blocking conditions (Hofer et al., 2017; Lim et al., 2016). The positive AMO phase, defined by anomalously warm North Atlantic sea surface temperatures (SSTs) after the global warming signal has been removed, is also significantly linked to surface melt over the entire GrIS potentially due to a strong connection between the AMO and NAO (Hanna et al., 2013; McLeod & Mote, 2016), although the direction of causality for this connection is debated (Gastineau & Frankignoul, 2015; Häkkinen et al., 2011; Peings & Magnusdottir, 2014). With atmospheric and oceanic variability established as dominant drivers of Greenland surface melt particularly for the past few decades, we analyze the extent to which these links are present in the absence of anthropogenic forcing and whether global warming will change or supersede these links in the future.
Gaire et al., 2019     An extreme drought was observed in the year 1707.  Also, the years 1705, 1706, 1784, 1786, 1809, 1810, 1813, 1821, 1849, 1858, 1861, 1909, 1967, 2006, and 2009 experienced severe drought conditions. Consecutive years with moderate drought were 1702–1706, 1783–1789, 1796–1798, 1812–1814, 1816–1827, 1846–1848, 1856–1864, 1873–1877, 1879–1882, 1899–1901, 1908–1911, and 1967–1968.  Three historic mega-drought events that occurred in Asia were also captured in our reconstruction: Strange Parallels drought (1756–1768), the East India drought (1790–1796), and the late Victorian Great Drought (1876–1878). Very few wet years (1776–1979, 1989, 1991, and 2003) were observed during the reconstruction period. Power spectrum analysis revealed drought variability at frequencies of 2.0–2.5, 3.0, 12.0, and 128 years, suggesting that drought in the region might be linked to broad-scale atmospheric-oceanic variabilities such as the El Niño-Southern Oscillation (ENSO) and the Atlantic Multidecadal Oscillation (AMO).

Najafi et al., 2019     Results show that large-scale climate, especially El Niño-Southern Oscillation (ENSO) and North Atlantic Oscillation (NAO) are strongly correlated with crop yield variability. Extensive maize harvesting regions in Europe and North America, rice in South America, Oceania and east of Asia, sorghum in west and southeast of Asia, North America and Caribbean and soybean in North and South America, Oceania and south of Asia experienced the influence of local climate variability in this period.
Bonan et al., 2019     This work identified that glaciers throughout Norway, Sweden and Svalbard are influenced by the NAO, which is associated with the routing and intensity of winter storms – consistent with several previous studies (e.g., Pohjola and Rogers, 1997; Nesje and others, 2000; Rasmussen, 2007; Nesje and others, 2008; Marzeion and Nesje, 2012; Trachsel and Nesje, 2015). However, dynamical adjustment also revealed that the glaciers residing farther north show progressively more influence of AMO-like anomalies, which suggests that while the NAO is the primary driver of glacier mass-balance variability in the region, both modes of climate variability act to drive anomalies in accumulation … AMO variability contributes to anomalously warmer or cooler summers over North America and western Europe (Sutton and Hodson, 2005), changes in northern hemispheric mean surface temperature (Knight and others, 2006) and Arctic sea-ice variability (Miles and others, 2014; Li and others, 2018) through the basin-wide redistribution of heat and mass. In the wintertime, a positive AMO phase and above-normal surface temperatures may elevate the rain-snow line, thereby altering the amount of snow accumulation on glaciers. … [T]he leading SLP predictor patterns show a center of negative correlation over the Scandinavian region. This is consistent with the persistent anti-cyclonic pressure system that tends to form over Scandinavia in the summer (Luterbacher and others, 2004). Such high-pressure systems are associated with clear skies, which result in the availability of more radiation for glacial melt.

Natural Variability, Hydroclimate Stability

Mao et al., 2019     Contemporary references to global warming pertain to the dramatic increase in monthly global land surface temperature (GLST) anomalies since 1976. In this paper, we argue that recent global warming is primarily a result of natural causesGlobal climate changes are controlled by major periodic factors that represent basic principles in climatology, such as solar radiation, atmospheric circulation and oceans. A number of scientists subjectively consider that the recent dramatic upward trends in monthly GLST anomalies represent non-periodic and irreversible changes and postulate that warming related to the global greenhouse effect has primarily been caused by anthropogenic emissions. However, with the decline of global warming, an increasing number of scientists have started to question this view [1]-[12]. There are two primary methods challenging the hypothesis that recent global warming is caused by anthropogenic emissions: the first method is to prove that the recent dramatic upward trend of monthly GLST anomalies is periodic, and the second method is to link global warming to major factors in nature. … In this paper, we have found that the dramatic upward rising signals can be perfectly fitted with periodic functions, which suggests that the major climate factors can still be the main reason for the recent global climate warming, and the secondary climate factor such as anthropogenic emissions might be the secondary reason. If we use the best function to predict the future behaviour of GLST, we can know that the downward trend for the monthly anomaly of GLST had already begun, and it will reach −0.6051˚C in 2111. The correlation study tells us that the dramatic anomalies can be seen in SST fields of different oceans, which might be the results of OSM [“Ocean Stabilization Machine”], and with the k-line diagram technique, we can see that most of the annual dramatically increasing GLST anomalies occur in El Niño years; and most of the annual dramatically decreasing GLST anomalies occur in La Niña years. These findings show us how OSM works. In a word, although there are many academic topics need to study further in future, we can still make a conclusion: “OSM” might play a very important role to cause global climate changes.

Maksym, 2019     Arctic sea ice has declined precipitously in both extent and thickness over the past four decades; by contrast, Antarctic sea ice has shown little overall change, but this masks large regional variability. Climate models have not captured these changes. But these differences do not represent a paradox. The processes governing, and impacts of, natural variability and human-induced changes differ markedly at the poles largely because of the ways in which differences in geography control the properties of and interactions among the atmosphere, ice, and ocean. The impact of natural variability on the ice cover is large at both poles, so modeled ice trends are not entirely inconsistent with contributions from both natural variability and anthropogenic forcing. Despite this concurrence, the coupling of natural climate variability, climate feedbacks, and sea ice is not well understood, and significant biases remain in model representations of the ice cover and the processes that drive it.
Bengtsson and Hodges, 2019     There are clear random 20-year linear trends in global mean surface temperature anomalies as well as significant regional 50-year linear trends. Even with an ensemble mean warming trend, typical of the early twenty-first century, a global hiatus in temperature of 20 years duration is possible to occur by chance. The results support the view that observed decadal and multi-decadal anomalies in the twentieth century were significantly influenced by internal processes of the climate system. This is particularly the case for the observed global warming trend of 1910–1940 and the global cooling trend of 1940–1970. Global mean precipitation hardly increases with time in the ensemble simulations, but in agreement with theory regional changes occur, with increasing precipitation in polar regions and in some tropical areas. In the subtropics there are reductions in precipitation. Long-lasting regional anomalies of significant amplitudes occur by chance in the ensemble integration.
Ashcroft et al., 2019     In this study we use rainfall data from a range of sources to examine four rainfall indices for Melbourne, Sydney and Adelaide for 1839–2017. We derive the total rainfall, number of raindays, wettest day of the month and the simple daily intensity index for each city over the past 178 years, and find relatively consistent relationships between all indices despite potential data quality issues associated with the historical data. We identify several extreme daily rainfall events in the pre-1900 period in Sydney and Melbourne that warrant further examination as they appear to be more extreme than anything in the modern record. We find a moderate and relatively stable relationship between El Niño–Southern Oscillation (ENSO) and annual variations of total rainfall and the number of raindays at all three cities over the research period, but no relationship between ENSO and the annual wettest day, in agreement with other studies using shorter time series.

Grise et al., 2019     In the NH, the contribution of GHGs to tropical expansion is much smaller and will remain difficult to detect in a background of large natural variability, even by the end of the twenty-first century. To explain similar recent tropical expansion rates in the two hemispheres, natural variability must be taken into account. Recent coupled atmosphere–ocean variability, including the Pacific decadal oscillation, has contributed to tropical expansion. However, in models forced with observed sea surface temperatures, tropical expansion rates still vary widely because of internal atmospheric variability.
Chung et al., 2019     Here, by conducting a comprehensive analysis based on multiple independent observational records, including satellite observations along with a large ensemble of model simulations, we objectively determine the relative contributions of internal variability and anthropogenic warming to the emergence of long-term PWC [Pacific Walker Circulation] trends. Our analysis shows that the satellite-observed changes differ considerably from the model ensemble-mean changes, but they also indicate substantially weaker strengthening than implied by the reanalyses. Furthermore, some ensemble members are found to reproduce the observed changes in the tropical Pacific. These findings clearly reveal a dominant role of internal variability on the recent strengthening of the PWC [Pacific Walker Circulation].
(press release     The study concludes that the observed strengthening of the Walker circulation from about 1990-2013 and its impact on western Pacific sea level, eastern Pacific cooling, drought in the Southwestern United States, was a naturally occurring phenomenon, which does not stand in contrast to the notion of projected anthropogenic climate change. Given the high levels of natural decadal variability in the tropical Pacific, it would take at least two more decades to detect unequivocally the human imprint on the Pacific Walker Circulation.
Turner et al., 2019     The trends in the annual total of precipitation from EPEs [extreme precipitation events] over 1979–2016 are small across most of the continent with only two large areas of statistically significant (p < 0.05) change in southern Dronning Maud Land and inland of the coast across 100–120°E (Figure S11). These are both areas where there have been significant trends in the annual precipitation total, as a result of greater ridging and amplification of planetary waves over East Antarctica resulting in more on onshore (offshore) flow close to 50°E (100°E). One area where there have been large temperature and circulation changes over 1979–2016 is the Antarctic Peninsula (Turner et al., 2005). This region experienced some of the largest temperature increases observed in the Southern Hemisphere during the second half of the twentieth century, but since the late 1990s there has been a regional cooling (Turner et al., 2016). This was reflected in an increase in the number of EPEs on the western side of the Antarctic Peninsula up until the end of the twentieth century followed by a subsequent decrease. During the twentieth century, positive trends in snow accumulation on the Antarctic Peninsula and eastern WAIS have contrasted with negative trends in snow accumulation in the western WAIS and Victoria Land (Thomas et al., 2017; Wang et al., 2017), consistent with a deepening ASL. However, there has been no significant change in the precipitation from EPEs [extreme precipitation events] over the period considered here.

Ortega et al., 2019     Highly variable SSTs in Tongoy Bay occurred during the last 2000 years (Figure 7c), and possibly earlier, in agreement with variable upwelling since ~3000 yr ago suggested by variable faunal assemblages (32°45’S) (Marchant et al, 1999). … Observed standardized annual precipitation and the 10-year running average at La Serena show a general decreasing trend (Figure 8a) reflecting the persistent aridification affecting the semi-arid coast of Chile. The linear trend over the whole observed period (1869–2016 CE) indicates that La Serena has had a 4% decrease in precipitation per decade, as previously documented by Schulz et al. (2011) and Quintana and Aceituno (2012). A similar calculation for CMIP5 simulations (1850-2005, historical simulations) indicates no significant trend over the 20th century. This difference between observations and simulations suggests that most of the observed trend is due to natural variability instead of a forced response to anthropogenic forcing.

Land et al., 2019     Very dry spring to mid-summer seasons lasting multiple years appeared in the decades AD 500/510s, 940s, 1170s, 1390s and 1160s. At the end of the AD 330s, a persistent multiyear drought with drastically reduced rainfall (w.r.t. 1901–2000) could be identified, which was the driest decade over the past 2,000 years in this region. In the AD 550s, 1050s, 1310s and 1480s, multi-year periods with high rainfall hit the Main region. In the spring to mid-summer of AD 338, precipitation was reduced by 38 % and in AD 357 it increased by 39 %.

Scharnweber et al., 2019     Here we present a simple but effective, data-driven approach to remove the recent non-climatic growth increase in tree-ring data. Accounting for the no-analogue calibration problem, a new hydroclimatic reconstruction for northern-central Europe revealed considerably drier conditions during the medieval climate anomaly (MCA) compared with standard reconstruction methods and other existing reconstructions. This demonstrates the necessity to account for fertilization effects in modern tree-ring data from affected regions before calibrating reconstruction models, to avoid biased results.

Hua et al., 2019     The reconstructed decadal hydroclimate variations are not correlated with any of the simulations, and the simulations are not correlated among themselves either, which strongly suggests that the decadal variability is not linked to the external climate forcing. In addition, the superposed epoch analysis also does not identify a response of simulated precipitation to volcanic eruptions. Therefore, precipitation variability in this region over the past millennium seems to have been driven by internal climate processes.

Nath and Luo, 2019     Using the Community Earth System Model (CESM)-Large Ensemble (LE) surface air temperature (SAT) data, we investigate the multidecadal changes in SAT variability over Central Indian landmass, particularly the Indo-Gangetic (IG) river basin. This region comes under the active influence of the Indian summer monsoon, and during the summer monsoon months (JJA), we observe an amplified cooling (< − 3 °C) trend (1961–2000) in SAT. This SAT trend is considered as a superposition of external forcings and natural climatic variability. The forced response is computed by averaging the trend in 35 ensemble members, which displays a moderate cooling trend due to aerosol-, ozone-, and volcano-only forcings. But the internal variability introduces a wide range of uncertainties in SAT, with majority of the members display a strong cooling trend in the Central Indian region. During the entire period, natural climatic variability dominates over the forced response, which strongly overrides the greenhouse gas (GHG) warming. Here, we separate out the influence of global climate variability on regional climate variability and identify the specific internal variability which is responsible for the multidecadal cooling trend in the analyzed region.
Fogt et al., 2019     In autumn, the anomalies are significant in the context of estimates of interannual variability and reconstruction uncertainty across most of the Antarctic continent, and the reconstructed patterns agree best with model-generated patterns when the simulation includes the forced response to tropical sea surface temperatures and external radiative forcing. In winter and spring, the reconstructed anomalies are less significant and are consistent with internal atmospheric variability alone. The specific role of tropical SST variability on pressure trends in these seasons is difficult to assess due to low reconstruction skill in the region of strongest tropical teleconnections, the large internal atmospheric variability, and uncertainty in the SST patterns themselves. Indirect estimates of pressure variability, whether through sea ice reconstructions, proxy records, or improved models and data assimilation schemes, will help to further constrain the magnitude of internal variability relative to the forced responses expected from SST trends and external radiative forcing.

Cloud/Aerosol Climate Influence

Wang et al., 2019     Unlike the rapid decline of Arctic sea ice in the warming climate, Antarctic sea ice extent exhibits a modest positive trend in the period of near four decades. In recent years, the fluctuation in Antarctic sea ice has been strengthened, including a decrease toward the lowest sea‐ice extent in February 2011 for the period of 1978‐2016 and a strong rebound in the summer of 2012. The sea‐ice recovery mainly occurs in the Weddell Sea, Bellingshausen Sea, Amundsen Sea, southern Ross Sea, and the eastern Somov Sea. This study offers a new mechanism for this summertime sea‐ice rebound. We demonstrate that cloudfraction anomalies in winter 2011 contributed to the positive Antarctic seaice anomaly in summer 2012. The results show that the negative cloudfraction anomalies in winter 2011 related to the largescale atmospheric circulation resulted in a substantial negative surfaceradiation budget, which cooled the surface and promoted more seaice growth. The sea‐ice growth anomalies due to the negative cloud forcing propagated by sea‐ice motion vectors from September 2011 to January 2012. The distribution of the sea ice anomalies corresponded well with the sea‐ice concentration anomalies in February 2012 in the Weddell Sea and eastern Somov Sea. Thus, negative cloudfraction anomalies in winter can play a vital role in the following summer sea ice distribution.
Sledd and L’Ecuyer, 2019      Decreases in sea ice extent and snow cover have, in turn, been linked to decreases in surface and TOA albedos over Arctic waters in observations. Sea ice has a much higher albedo than open ocean, so when sea ice melts the ocean absorbs more SW radiation. More SW radiation at the surface warms the ocean and further melts the sea ice, creating the ice-albedo feedback central to Arctic amplification. … Yet while sea ice and snow play a key role in the Arctic energy balance, their influence is strongly modulated by the atmosphere and, in particular, cloud cover. Clouds affect both LW and SW radiation throughout the atmospheric column. They can decrease the SW radiation that reaches the surface as well as increase the down-welling LW radiation. Thus, clouds modulate surface melting, warming the surface by trapping thermal radiation or cooling it by reflecting SW radiation. The presence of clouds also has implications for the ice-albedo feedback. We can readily see in satellite imagery that the contrast between ice-covered and open water is completely obscured by opaque cloud cover. Studies have found that the TOA albedo changes less in response to reduced surface cover than the surface albedo.
Nomokonova et al., 2019     Clouds play a crucial role in the energy budget and in the hydrological cycle. On the one hand, clouds scatter solar radiation back to space, leading to a shortwave cooling effect at the surface. On the other hand, clouds emit longwave radiation and therefore warm the surface. The impact of clouds on the energy budget depends on their macrophysical (cloud thickness, cloud-top and cloud-base altitudes) and microphysical (phase, size, and concentration) properties (Sedlar et al., 2012; Dong et al., 2010). … The net cloud radiative forcing in the Arctic influences sea ice coverage and leads to more open water that in turn affects heat exchange between ocean and atmosphere (Serreze et al., 2009; Kapsch et al., 2013). Extended periods of open ocean increase the moisture content in the atmosphere and therefore might enhance cloud coverage (Rinke et al., 2013; Palm et al., 2010; Kay and Gettelman, 2009; Mioche et al., 2015; Bennartz et al., 2013). Beyond the radiative feedbacks clouds are crucial for precipitation formation that significantly affects the Arctic climate. Precipitated water forms rivers and sustains a glacier flow into the sea, thus influencing the salinity of the Arctic ocean. Being essential for snowmelt (Zhang et al., 1996), sea ice reduction (Kay et al., 2008; Kay and Gettelman, 2009), and affecting the permafrost stability, Arctic clouds have a significant impact on productivity and variety in marine and terrestrial environments and thus influence the Arctic ecosystem (Vihma et al., 2016). … We found that the temperature distribution of single-layer liquid clouds is narrow with temperatures typically ranging from −10 to +5 ◦C. Similar results are also found for the ICON model. However, the distribution of the liquid phase for mixed-phase clouds is one of the major differences between the model and observations. The observed distribution ranges from −25 to +10 ◦C, while in the ICON model the liquid phase is concentrated in the temperature range from −10 to +5 ◦C. This difference results in a significant divergence between observed and modeled single-layer ice and mixed-phase clouds.

Volcanic/Tectonic Climate Influence

Bragato and Holzhauser, 2019     This study has suggested that an unusual, 50-year-long episode of four massive tropical volcanic eruptions had triggered the LIA between 1275 and 1300 AD. The persistence of cold summers following the eruptions is best explained by a subsequent expansion of sea ice and a related weakening of Atlantic currents, according to computer simulations conducted for the study. This research, which has used analyses of patterns of dead vegetation, ice and sediment core data and computer climate models, has provided new evidence on the onset of the LIA. Scientists have theorized that the LIA was caused by a decreased summer solar radiation, with erupting volcanoes which cooled the planet by ejecting sulfates and other aerosol particles, which reflected the sunlight back into the space or by a combination of the two processes. The specific onset of the cold times marking the starting point of the LIA has been clearly identified for the first time, providing an understandable climate feedback system that explains how this cold period could be sustained for a long period of time. If the climate system is hit again and again by cold conditions over a relatively short period, in this case from the volcanic eruptions, there appears to be a cumulative cooling effect. The simulations constructed in this study have shown that the volcanic eruptions had a strong cooling effect. The eruptions could have triggered a chain reaction, affecting sea ice and ocean currents in a way that lowered temperatures for centuries.

Gupta et al., 2019     A coupled climate model with idealized representations of atmosphere, ocean, sea ice, and land is used to investigate transitions between global climate equilibria. The model supports the presence of climates with limited ice cover (Warm), a continuum of climates in which sea ice extends down into the midlatitudes and the tropics (Cold), together with a completely ice-covered earth (Snowball). Transitions between these states are triggered through volcanic eruptions, where the radiative effect of stratospheric sulfur emissions is idealized as an impulse reduction in incoming solar radiation. Snowball transitions starting from the Cold state are more favorable than from the Warm state, because less energy must be extracted from the system. However, even when starting from a Cold climate, Toba-like volcanic events (cooling of order −100 W m−2) must be sustained continuously for several decades to glaciate the entire planet. When the deep ocean is involved, the volcanic response is characterized by relaxation time scales spanning hundreds to thousands of years. If the interval between successive eruptions is significantly shorter (years to decades) than the ocean’s characteristic time scales, the cumulative cooling can build over time and initiate a state transition. The model exhibits a single hysteresis loop that connects all three climate equilibria. When starting from a Snowball, the model cannot access the Cold branch without first transitioning to an ice-free climate and completing the hysteresis loop. By contrast, a Cold state, when warmed, transitions to the Warm equilibrium without any hysteresis.

Antarctic Ice Melting In High Geothermal Heat Flux Areas

Dziadek et al., 2019    Elevated geothermal surface heat flow in the Amundsen Sea Embayment, West Antarctica … Basal ice sheet temperatures are controlled by a basal heat gradient (Siegert and Dowdeswell, 1996) in addition to frictional heat generated from ice deformation and basal sliding. The basal heat gradient is the sum of heat produced from basal sliding and geothermal heat flow (Siegert, 2000).  … it has been shown that the GHF [geothermal heat flow] from one subglacial volcanic center could produce enough basal meltwater to offset the basal energy balance and lubricate parts of an ice sheet bed that would otherwise remain frozen (Vogel and Tulaczyk, 2006). … Our results show regionally elevated and heterogeneous GHF (mean of 65 mW m−2) in the Amundsen Sea Embayment. Considering thermal blanketing effects, induced by inflow of warmer water and sedimentary processes, the estimated GHF ranges between 65 mWm−2 and 95 mW m−2.
Pittard et al., 2019     Melting at the base of the Antarctic Ice Sheet influences ice dynamics and our ability to recover ancient climatic records from deep ice cores. Basal melt rates are affected by geothermal flux, one of the least constrained properties of the Antarctic continent. Estimates of Antarctic geothermal flux are typically regional in nature, derived from geological, magnetic or seismic data, or from sparse point measurements at ice core sites. We analyse ice-penetrating radar data upstream of South Pole revealing a ~100 km long and 50 km wide area where internal ice sheet layers converge with the bed. Ice sheet modelling shows that this englacial layer configuration requires basal melting of up to 6 ± 1 mm a−1 and a geothermal flux of 120 ± 20 mW m−2, more than double the values expected for this cratonic sector of East Antarctica. We suggest high heat producing Precambrian basement rocks and hydrothermal circulation along a major fault system cause this anomaly. We conclude that local geothermal flux anomalies could be more widespread in East Antarctica. Assessing their influence on subglacial hydrology and ice sheet dynamics requires new detailed geophysical observations, especially in candidate areas for deep ice core drilling and at the onset of major ice streams.

Mass Extinction Events Caused By Glaciation, Sea Level Fall

Fujisaki et al., 2019     To constrain the redox conditions and related nitrogen cycles during the Middle Permian (Guadalupian) to latest Late Permian (Lopingian) deep mid-Panthalassa, we determined the abundances of major, trace, and rare earth elements along with the carbon and nitrogen isotope ratios in shales interbedded with deep-sea cherts that are well-exposed at the Gujo-Hachiman section in the Mino-Tanba belt, SW Japan. … However, unlike the oxic and nitrate-rich deep-Panthalassa, we speculate that oxygen-depleted (i.e., anoxic/euxinic) and bioavailable nitrogen-poor conditions developed in the deep Tethys immediately before the Guadalupian-Lopingian boundary (G-LB). These environmental stresses were potentially driven by a global cooling episode (Kamura event) together with the unique paleogeography, i.e., no contact with polar ice caps in the Tethyan Ocean. Upwelling of the anoxic watermass accumulated in the deep Tethys during the global cooling episode likely triggered oceanic anoxia in the shallow-marine regions around the G-LB [Guadalupian-Lopingian boundary, Mid- to Late Permian], which eventually resulted in the G-LB mass extinction. … In the latest Guadalupian (Capitanian), the appearance of the global cooling episode was proposed based on various lines of evidence; e.g., the lowest sea-level during the Phanerozoic (Haq and Schutter, 2008), the preferential extinction of tropically adapted fauna (Isozaki and Aljinović, 2009), the migration of mid-latitude fauna toward tropical domains (Shen and Shi, 2002), and the occurrences of mid-latitude tillites (Fujimoto et al., 2012) and alpine glacial deposits in high altitudes (Fielding et al., 2008). The high δ13Ccarb values during this period were also interpreted to indicate high primary productivity and leading to an effective burial of organic matter promoted by the global cooling episode (Kamura event; Isozaki et al., 2007a, 2007b, 2011). The global cooling episode potentially affected biological activity in the shallowmarine domains; i.e., the low eustatic levels invoked delivery of fluvial organic matter to shelf because of the increased land area, which likely resulted in increase of organic matter, expansion of the oxygen minimum zone (OMZ), and enhanced denitrification in the water column.
Smolarek-Lach et al., 2019     Mercury Spikes Indicate a Volcanic Trigger for the Late Ordovician Mass Extinction Event … We conclude that our Hg and Hg/TOC values were associated with volcanic pulses which triggered the massive environmental changes resulting in the Late Ordovician mass extinction. … Mercury enrichments have also been described for the middle and latest Permian extinctions. Sanei et al.’s study of the latest Permian mercury enrichment in the Canadian High Arctic, attributed this to emissions from the Siberian Traps [flood volcanism] with deleterious environmental consequences. … [T]he Hg enrichment in the Katian geochemical record (the ornatus anomaly) is interpreted as a volcanic event that triggered severe cooling. It has been suggested that the upper pacificus anomaly is connected with a volcanic eruption which triggered an albedo catastrophe and the rapid expansion of ice sheets.

The CO2 Greenhouse Effect – Climate Driver?

Varotsos and Efstathiou, 2019     The enhancement of the atmospheric greenhouse effect due to the increase in the atmospheric greenhouse gases is often considered as responsible for global warming (known as greenhouse hypothesis of global warming). In this context, the temperature field of global troposphere and lower stratosphere over the period 12/1978–07/2018 is explored using the recent Version 6 of the UAH MSU/AMSU global satellite temperature datasetOur analysis did not show a consistent warming with gradual increase from low to high latitudes in both hemispheres, as it should be from the global warming theory. In addition, in the lower stratosphere the temperature cooling over both poles is lower than that over tropics and extratropics. To study further the thermal field variability we investigated the long-range correlations throughout the global lower troposphere-lower stratosphere region. The results show that the temperature field displays power-law behaviour that becomes stronger by going from the lower troposphere to the tropopause. This power-law behaviour suggests that the fluctuations in global tropospheric temperature at short intervals are positively correlated with those at longer intervals in a power-law manner. The latter, however, does not apply to global temperature in the lower stratosphere. This suggests that the investigated intrinsic properties of the lower stratospheric temperature are not related to those of the troposphere, as is expected by the global warming theory. In summary, the tropospheric temperature has not increased over the last four decades, in both hemispheres, in a way that is more amplified at high latitudes near the surface. In addition, the lower stratospheric temperature did not decline as a function of latitude. Finally, the intrinsic properties of the tropospheric temperature are different from those of the lower stratosphere. Based on these results and bearing in mind that the climate system is complicated and complex with the existing uncertainties in the climate predictions, it is not possible to reliably support the view of the presence of global warming in the sense of an enhanced greenhouse effect due to human activities.

Ollila, 2019     The temperature effects of the water and CO2 are based on spectral analysis calculations, which show that water is 11.8 times stronger a GH gas than CO2 in the present climate. … The variable labeled “Factor X” is also depicted in Figure 7; it is the difference between the measured 11 years average temperature and the warming effects of CO2, water and ENSO events. Factor X is needed to explain the observed warming. It is a combination of natural forces like the activity changes of the sun. It is easy to notice that the short-term temperature changes – mainly ENSO events – very closely correlate to the total precipitable water (TPW) changes. … There are essential features in the long-term trends of temperature and TPW, which are calculated and depicted as mean values 11 years running. The temperature has increased about 0.4°C since 1979 and has now paused at this level. The long-term trend of TPW [total precipitable water] effects shows that it has slightly decreased during the temperature-increasing period from 1979 to 2000. This means that the absolute water amount in the atmosphere does not follow the temperature increase, but is practically constant, reacting only very slightly to the long-term trends of temperature changes. The assumption that relative humidity is constant and that it amplifies the GH gas changes over the longer periods by doubling the warming effects finds no grounds based on the behavior of the TWP trend. The positive water feedback exists only during the short-term ENSO events (≤4 years).

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