Part 3. Natural Climate Change Observation, Reconstruction
Lack Of Anthropogenic/CO2 Signal In Sea Level Rise (22)
Mörner, 2017 Coastal morphology, stratigraphy, radiocarbon dating, archaeological remains, historical documentation, and tide gauge records allowed us to establish a very firm and detailed record of the changes in sea level in Goa over the last 500 years. It is an oscillation record: a low level in the early 16th century, a ~50-cm high[er than now] level in the 17th century, a level below present sea level in the 18th century, a ~20-cm high level in the 19th and early 20th centuries, a ~20-cm fall in 1955–1962, and a virtually stable level over the last 50 years. This sea level record is almost identical to those obtained in the Maldives and in Bangladesh. The Indian Ocean seems to lack records of any alarming sea-level rise in recent decades; on the contrary, 10 sites analyzed indicate a sea level remaining at about 60.0, at least over the last 50 years or so.
Sasaki et al., 2017 Sea level variability around Japan from 1906 to 2010 is examined using a regional ocean model, along with observational data and the CMIP5 historical simulations. The regional model reproduces observed interdecadal sea level variability, e.g., high sea level around 1950, low sea level in the 1970s, and sea level rise during the most recent three decades, along the Japanese coast. Sensitivity runs reveal that the high sea level around 1950 was induced by the wind stress curl changes over the North Pacific, characterized by a weakening of the Aleutian Low. In contrast, the recent sea level rise is primarily caused by heat and freshwater flux forcings. That the wind-induced sea level rise along the Japanese coast around 1950 is as large as the recent sea level rise highlights the importance of natural variability in understanding regional sea level change on interdecadal timescales.
Montecino et al., 2017 Our estimation of the SLC in the Chilean coast revealed an overall increase in sea level. The sea level in Chile does not strictly follow the global trend of the past two decades (~3 mm year−1), but rather a slight agreement (from 1.2 to 0.6 mm year−1) from Arica up to Puerto Montt approximately, with the exception of PTAR and PWIL TGs, where we found a decrease of −0.9 and −0.8 mm year−1, respectively.
Rani et al., 2017 In the present study, an attempt has been made to understand the variability of mean sea level (MSL) over east and west coast of India during 1973–2010. … The observations also reveal an increase of 1.353 mm/year on the east coast and observed a total 0.372 mm/ year on the west coast.
Parekh et al., 2017 The rate of sea level rise over the Arabian Sea is about 0.5–3 mm/year, whereas over the Bay of Bengal, it is 0.75–6 mm/year. Major contributors to these changes in the Indian Ocean are steric effect and short-term climate variability such as El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole. This affirms that sea level trends over north Indian Ocean get modulated by inter-annual and decadal scale natural climate variability. The inter-annual variability is stronger than decadal variability, which in turn is stronger than the long-term sea level trend. Sea level change in the Indian Ocean is about 1.5 mm/year in the past sixty years or so, whereas the global sea level trends are a bit higher.
McAneney et al., 2017 Global averaged sea-level rise is estimated at about 1.7 ± 0.2 mm year−1 (Rhein et al. 2013), however, this global average rise ignores any local land movements. Church et al. (2006) and J. A. Church (2016; personal communication) suggest a long-term average rate of relative (ocean relative to land) sea-level rise of ∼1.3 mm year. …The data show no consistent trend in the frequency of flooding over the 122-year [1892-2013] duration of observations despite persistent warming of air temperatures characterized in other studies. On the other hand, flood frequencies are strongly influenced by ENSO phases with many more floods of any height occurring in La Niña years. … In terms of flood heights, a marginal statistically significant upward trend is observed over the entire sequence of measurements. However, once the data have been adjusted for average sea-level rise of 1.3 mm year−1 over the entire length of the record, no statistically significance remains, either for the entire record, or for the shortened series based on higher quality data. The analysis of the uncorrected data shows how the choice of starting points in a time series can lead to quite different conclusions about trends in the data, even if the statistical analysis is consistent. … In short, we have been unable to detect any influence of global warming at this tropical location on either the frequency, or the height of major flooding other than that due to its influence on sea-level rise.
Zerbini et al., 2017 Our study focuses on the time series of Alicante, in Spain, Marseille, in France, Genoa, Marina di Ravenna (formerly Porto Corsini), Venice and Trieste, in Italy. After removing the vertical land motions in Venice and Marina di Ravenna, and the inverted barometer effect at all the sites, the linear long period sea-level rates were estimated. The results are in excellent agreement ranging between + 1.2 and + 1.3 mm/year for the overall period from the last decades of the 19th century till 2012. The associated errors, computed by accounting for serial autocorrelation, are of the order of 0.2–0.3 mm/year for all stations, except Alicante, for which the error turns out to be 0,5 mm/year. … Our estimated rates for the northern Mediterranean, a relatively small regional sea, are slightly lower than the global mean rate, + 1.7 ± 0.2 mm/year, recently published in the IPCC AR5 (Intergovernmental Panel on Climate Change 5th Assessment Report) (Church et al., 2013), but close enough, if uncertainties are taken into account. It is known that Mediterranean stations had always had lower trends than the global-average ones. Our regional results, however, are in close agreement with the global mean rate, + 1.2 mm/year, published by Hay et al. (2015) which is currently being discussed by the oceanographic community
Watson, 2017 The analysis in this paper is based on a recently developed analytical package titled ‘‘msltrend,’’ specifically designed to enhance estimates of trend, real-time velocity, and acceleration in the relative mean sea-level signal derived from long annual average ocean water level time series. Key findings are that at the 95% confidence level, no consistent or compelling evidence (yet) exists that recent rates of rise are higher or abnormal in the context of the historical records available across Europe, nor is there any evidence that geocentric rates of rise are above the global average. It is likely a further 20 years of data will distinguish whether recent increases are evidence of the onset of climate change–induced acceleration.
Eghbert et al., 2017 In September 2015, altimetry data show that sea level was at its lowest in the past 12 years [Indonesia], affecting corals living in the bathymetric range exposed to unusual emersion. In March 2016, Bunaken Island (North Sulawesi) displayed up to 85% mortality on reef flats dominated by Porites, Heliopora and Goniastrea corals with differential mortality rates by coral genus. … [R]apid sea level fall could be more important in the dynamics and resilience of Indonesian reef flat communities than previously thought. This study reports coral mortality in Indonesia after an El Niño-induced sea level fall. The fact that sea level fall, or extremely low tides, induces coral mortality is not new, but this study demonstrates that through rapid sea level fall, the 2015–2016 El Niño has impacted Indonesian shallow coral reefs well before high sea surface temperature could trigger any coral bleaching. Sea level fall appears as a major mortality factor for Bunaken Island in North Sulawesi, and altimetry suggests similar impact throughout Indonesia.
Holocene Sea Levels Much Higher When CO2 Levels Much Lower
Lecea et al., 2017 Ramsay (1995) produced a 9 kyr BP record of sea-level changes from the South African east coast, that showed sea levels reached a high stand of +3.5 m [above present] at 4.65 kyr BP. Similar high stands have been recorded elsewhere in the Southern Hemisphere, on the west coast of South Africa (0 – 3 m [above present], Compton, 2001), in south Australia (1 – 3 m [above present], Belperio et al., 2002), south- and north-east Australia (1.7 m [above present], Baker et al., 2001; 2 m [above present], Larcombe et al., 1995, respectively) and Brazil (2.1 m [above present], Angulo et al., 2006). In South Africa this was followed by a drop below present level before rising to another high stand at 1.6 kyr BP (Compton, 2001; Ramsey, 1995). … In Mozambique, Norström et al., (2012) identified a sea-level highstand ~3 m above present at ~ 6.6 kyr BP.
Das et al., 2017 In the absence of any evidence of land-level changes, the study suggests that at around 6 ka to 3 ka [6,000 to 3,000 years ago], the sea was approximately 2 m higher than present.
Fontes et al., 2017 During the early-middle Holocene there was a rise in RSL [relative sea level] with a highstand at about 5350 cal yr BP [calendar years before present] of 2.7 ± 1.35 m [higher than present], which caused a marine incursion along the fluvial valley.
Yoon et al., 2017 Songaksan is the youngest eruptive centre on Jeju Island, Korea, and was produced by a phreatomagmatic eruption in a coastal setting c. 3.7 ka BP [3,700 years before present]. The 1 m thick basal portion of the tuff ring shows an unusually well-preserved transition of facies from intertidal to supratidal, from which palaeo-high-tide level and a total of 13 high-tide events were inferred. Another set of erosion surfaces and reworked deposits in the middle of the tuff ring, as high as 6 m above present mean sea level, is interpreted to be the product of wave reworking during a storm-surge event that lasted approximately three tidal cycles. … The reworked deposits alternate three or four times with the primary tuff beds of Units B and C and occur as high as 6 m above present mean sea level or 4 m above high-tide level (based on land-based Lidar terrain mapping of the outcrop surface).
Bini et al., 2017 The main conclusion is that the relative sea-level between c. 7000 and 5300 cal. yr BP was in the range of c. 2–4 m a.s.l. [above present mean sea level], with a mean value of c. 3.5 m a.s.l. … Initial glacio-hydro-isostatic models of the Patagonian coast [Argentina] suggested that the shoreline could be characterized by currently raised beaches, which started to form as soon as ice-sheet melting ceased (Clark et al., 1978). A more recent model (Milne and Mitrovica, 2008) predicted that RSLs [relative sea levels] might have exceeded present by c. 5 m at 6000 cal. yr BP. [T]he altimetric and chronological data of the valleymouth terraces show a highstand between c. 7000 and 6600 cal. yr BP at c. 4 m a.s.l. [4 meters above present mean sea level], followed by a progressive fall to c. 2–2.5 m between 6200 and 5300 cal. yr BP.
Marwick et al., 2017 (full paper) Sinsakul (1992) has summarised 56 radiocarbon dates of shell and peat from beach and tidal locations to estimate a Holocene sea level curve for peninsula Thailand that starts with a steady rise in sea level until about 6 k BP, reaching a height of +4 m amsl (above [present] mean sea level). Sea levels then regressed until 4.7 k BP, then rising again to 2.5 m amsl at about 4 k BP. From 3.7 k to 2.7 k BP there was a regressive phase, with transgression starting again at 2.7 k BP to a maximum of 2 m amsl at 2.5 k BP. Regression continued from that time until the present sea levels were reached at 1.5 k BP. … Tjia (1996) collected over 130 radiocarbon ages from geological deposits of shell in abrasion platforms, sea-level notches and oyster beds and identified a +5 m [above present] highstand at ca. 5 k BP in the Thai-Malay Peninsula. … Sathiamurthy and Voris (2006) summarise the evidence described above as indicating that between 6 and 4.2 k BP, the sea level rose from 0 m to +5 m [above present] along the Sunda Shelf [+2.8 mm/yr], marking the regional mid-Holocene highstand. Following this highstand, the sea level fell gradually and reached the modern level at about 1 k BP.
May et al., 2017 [T]he mid-Holocene sea-level highstand of Western Australia [was] at least 1–2 m above present mean sea level. … Between approximately 7000 and 6000 years BP, post-glacial RSL [relative sea level] reached a highstand of 1-2 m above the present one, followed by a phase of marine regression (Lambeck and Nakada, 1990; Lewis et al., 2013).
Kane et al., 2017 The high stand is documented across the equatorial Pacific with peak sea-level values ranging from 0.25 to 3.00 m above present mean sea level (MSL) between 1000 and 5000 yr BP (Fletcher and Jones, 1996; Grossman et al., 1998; Dickinson, 2003; Woodroffe et al., 2012). Woodroffe et al. (2012) argues that Holocene sea-level oscillations of a meter or greater are likely to have been produced by local rather than global processes.
Meltzner et al., 2017 Half-metre sea-level fluctuations on centennial timescales from mid-Holocene corals of Southeast Asia … RSL [relative sea level] history between 6850 and 6500 cal years BP that includes two 0.6 m fluctuations, with rates of RSL change reaching 13±4 mm per year. … Here RSL rose to an initial peak of +1.9 m [above present] at 6,720 cal years BP, then fell rapidly to a lowstand of +1.3 m, remaining at about that level for ∼100 years, before rising to a second peak at +1.7 m shortly after 6,550 cal years BP. Around 6,480 cal years BP, RSL appears to have fallen again to +1.3 m before rising to a third peak at +1.6 m or higher. … The peak rate of RSL rise, averaged over a 20-year running time window over the period of study (∼6,850–6,500 cal years BP), is +9.6±4.2 mm per year (2σ); the peak rate of RSL fall is −12.6±4.2 mm per year. … To put the ∼0.6 m mid-Holocene fluctuations in context, annual mean sea level in some modern tide-gauge records is seen to change by as much as 0.2–0.3 m on interannual timescales, and the interannual s.d. of sea surface height between 1979 and 2013 approached 0.1 m in some portions of the western Pacific. The central dome of each microatoll grew during a period when RSL was high; RSL then fell rapidly, killing the upper portions of the corals; RSL then stabilized at a lower elevation, forming a series of low concentric annuli ∼0.6 m higher than present-day analogues; RSL [relative sea level] then rose ∼0.6 m in less than a century, allowing the coral to grow upward to 1.2 m higher than modern living corals.
Khan et al., 2017 Only Suriname and Guyana [Caribbean] exhibited higher RSL [relative sea level] than present (82% probability), reaching a maximum height of ∼1 m [above present] at 5.2 ka [5,200 years ago]. … Because of meltwater input, the rates of RSL [relative sea level] change were highest during the early Holocene, with a maximum of 10.9 ± 0.6 m/ka [1.09 meters per century] in Suriname and Guyana and minimum of 7.4 ± 0.7 m/ka [0.74 meters per century] in south Florida from 12 to 8 ka [12,000 to 8,000 years ago].
Dechnik et al., 2017 [I]t is generally accepted that relative sea level reached a maximum of 1–1.5 m above present mean sea level (pmsl) by ~7 ka [7,000 years ago] (Lewis et al., 2013) … Over the last few decades, the global decline of modern reefs has been linked to environmental and climatic changes in response to anthropogenic activities. However, recent geological and ecological research on fossil reefs in the Great Barrier Reef (GBR) and wider Indo-Pacific identified intervals of significant reef “turn-off” in response to natural environmental forces earlier in their development during the mid- to late Holocene. … Increased upwelling, turbidity and cyclone activity in response to increased sea-surface temperature (SST’s), precipitation and El-Nino Southern Oscillation variability have been ruled out as possible mechanisms of reef turn-off for the mid-outer platform reefs. Rather, a fall (~0.5 m) in relative sea level at 4–3.5 ka is the most likely explanation for why reefs in the northern and southern regions turned off during this time. … Similar hiatuses in Holocene reef growth were identified in Japan from about 5.9 to 5.8 ka, 4.4 to 4.0 ka and from 3.3 to 3.2 ka. They were attributed to oscillating sea level and relatively cold sea-surface temperatures.
Leonard, 2017 The resultant palaeo-sea-level reconstruction revealed a rapid lowering of RSL of at least 0.4 m from 5500 to 5300 yBP following a RSL [relative sea level] highstand of ~0.75 m above present from ~6500 to 5500 yBP. RSL then returned to higher levels before a 2000-yr hiatus in reef flat corals after 4600 yBP. The RSL oscillations at 5500 yBP and 4600 yBP coincide with both substantial reduction in reef accretion and wide spread reef “turn-off”, respectively, thereby suggesting that oscillating sea level was the primary driver of reef shut down on the GBR.
Guo et al., 2017 The upper 250 meter-long sediment core of Site U1391 (1085 m water depth) retrieved from the Portuguese margin in the Northeast Atlantic Ocean was adopted for the benthic foraminiferal analyses to disclose the variations in Mediterranean Outflow Water (MOW) intensity over the last ~ 0.9 Ma [900,00 years]. The strongest MOW [Mediterranean Outflow Water] intensity during MIS 11 [400,000 years ago] confirms the climatic influence of waving sea level on the MOW current by its +20 m high-stand above the present sea level.
No Net Warming During 20th (21st) Century (11)
Flannery et al., 2017 The early part of the reconstruction (1733–1850) coincides with the end of the Little Ice Age, and exhibits 3 of the 4 coolest decadal excursions in the record. However, the mean SST estimate from that interval during the LIA is not significantly different from the late 20th Century SST mean. The most prominent cooling event in the 20th Century is a decade centered around 1965. This corresponds to a basin-wide cooling in the North Atlantic and cool phase of the AMO.
Steiger et al., 2017 Through several idealized and real proxy experiments we assess the spatial and temporal extent to which isotope records can reconstruct surface temperature, 500 hPa geopotential height, and precipitation. We find local reconstruction skill to be most robust across the reconstructions, particularly for temperature and geopotential height, as well as limited non-local skill in the tropics. These results are in agreement with long-held views that isotopes in ice cores have clear value as local climate proxies, particularly for temperature and atmospheric circulation.
Köse et al., 2017 The reconstruction is punctuated by a temperature increase during the 20th century; yet extreme cold and warm events during the 19th century seem to eclipse conditions during the 20th century. We found significant correlations between our March–April spring temperature reconstruction and existing gridded spring temperature reconstructions for Europe over Turkey and southeastern Europe. … During the last 200 years, our reconstruction suggests that the coldest year was 1898 and the warmest year was 1873. The reconstructed extreme events also coincided with accounts from historical records. … Further, the warming trends seen in our record agrees with data presented by Turkes and Sumer (2004), of which they attributed [20th century warming] to increased urbanization in Turkey. Considering long-term changes in spring temperatures, the 19th century was characterized by more high-frequency fluctuations compared to the 20th century, which was defined by more gradual changes and includes the beginning of decreased DTRs [diurnal temperature ranges] in the region (Turkes and Sumer, 2004).
Imada et al., 2017 Since the late 1990s, land surface temperatures over Japan have increased during the summer and autumn, while global mean temperatures have not risen in this duration (i.e., the global warming hiatus). In contrast, winter and spring temperatures in Japan have decreased.
Fernández-Fernández et al., 2017 The abrupt climatic transition of the early 20th century and the 25-year warm period 1925–1950 triggered the main retreat and volume loss of these glaciers since the end of the ‘Little Ice Age’. Meanwhile, cooling during the 1960s, 1970s and 1980s altered the trend, with advances of the glacier snouts. Between the ‘Little Ice Age’ and the present day, the mean annual air temperature and mean ablation season air temperature increased by 1.9°C and 1.5°C, respectively, leading to a 40–50 m rise in the equilibrium line altitude (ELA) of the glaciers during this period. … The retreat rate intensified in the period 2000–2005 compared with 1994–2000, but did not reach the rates recorded before 1946. … In the second half of the 20th century, the retreat decelerated considerably, reflected in the lowest values around 1985 (5.2 m yr−1) and a trend shift in 1994, with an advance observed in Gljúfurárjökull. The trend then altered again and Gljúfurárjökull retreated in the years 1994–2005. … During the period 1898–1946, the snout of Gljúfurárjökull retreated 635 m, almost two-thirds of the total distance from the LIA maximum (1898–1903) to 2005, at an average rate of 13.2 m yr−1. … The trend in Western Tungnahryggsjökull during the first half of the 20th century was a more rapid retreat, showing the highest average rates of the whole period (19.5 m yr−1). By 1946, this glacier had retreated almost 90% of the total recorded between the LIA maximum (1868) and 2005. … Just as in the glaciers described above, the retreat of the Eastern Tungnahryggsjökull from its LIA position was more intense during the first half of the 20th century, and in 1946 its snout was only 200 m from its current position. … The 2000 aerial photograph shows that an advance of at least 41 m had taken place since 1985. Nevertheless, between 2000 and 2005, the snout retreated 17 m, even more slowly than Western Tungnahryggsjökull. [Between 1985 and 2005, the Eastern Tungnahryggsjökull glacier did not retreat, but instead advanced by a net total of 24 meters.]
Cai and Liu et al., 2017 2003– 2009 was the warmest period in the reconstruction. 1970– 2000 was colder than the last stage of the Little Ice Age (LIA).
A Warmer Past/Non-Hockey Stick Reconstructions (33)
Büntgen et al., 2017 Spanning the period 1186-2014 CE, the new reconstruction reveals overall warmer conditions around 1200 and 1400, and again after ~1850. The coldest reconstructed summer in 1258 (-4.4°C wrt 1961-1990) followed the largest known volcanic eruption of the CE. The 20th century is characterized by pronounced summer cooling in the 1970s, subsequently rising temperatures until 2003, and a slowdown of warming afterwards. Little agreement is found with climate model simulations that consistently overestimate recent summer warming and underestimate pre-industrial temperature changes. … [W]hen it comes to disentangling natural variability from anthropogenically affected variability the vast majority of the instrumental record may be biased. … Although the causes of the recently measured slowdown in global and regional warming during the last decade are still debated (Karl et al. 2015; Fyfe et al. 2016), our study provides the first long-term proxy evidence for this temperature decline over the western Mediterranean basin. This finding is in line with local, regional and sub-continental meteorological observations, and consistent with the observations by Gleisner et al. (2015) that the post-2003 pause in rising mean surface temperatures is most strongly expressed at mid-latitudes. … The reconstructed long-term variability exceeds the pre-industrial multi-decadal to centennial variability in four state-of-the-art climate model simulations. This mismatch between the proxy reconstructions and the four model simulations is in line with a general tendency of state-of-the-art climate model simulations to underestimate the amplitude of reconstructed natural low-frequency temperature variability during the last millennium (Bothe et al. 2013; Fernández-Donado et al. 2013; Phipps et al. 2013; Luterbacher et al. 2016; Ljungqvist et al. 2012). Such disagreement might indicate that the role of internal unforced variability is greater than expected (Goosse 2017; Matsikaris et al. 2016), and/or that the climate sensitivity to the prescribed forcings needs adjustment. … [S]tate-of-the-art climate models are usually driven by a relatively dampened amplitude of long-term changes in solar activity (Schmidt et al. 2011,2012).
Demezhko et al., 2017 Temperature and heat flux changes at the base of Laurentide ice sheet inferred from geothermal data … The temperature curve reveals a sharp rise in the early Holocene (12−10-ka BP) and a relatively stable warm climate of interglacial, while the heat flux began to increase about 2 ka earlier, reached a maximum at the beginning of the Holocene, and then decreased. … GSTH [ground surface temperature histories] reconstructed under SD=0.02 W/(m K) reveals major climatic events of the last 100 ka including the Last Glacial Maximum around 20 ka BP with a minimum temperature −2.7°C, the Holocene Climatic Optimum around 5 ka BP with the maximal temperature+8.4°C, and subsequent cooling to the contemporary mean surface temperature +4°C. [Surface temperatures were 4.4°C higher than present 5,000 years ago]. … GST [ground surface temperature] and SHF [surface heat flux] histories differ substantially in shape and chronology. Heat flux changes ahead temperature changes by 500–1000 years. … These results (Fig. 4d) indicate an abrupt increase of summer (from May to August) temperatures between 12 and 10 ka BP, relative stabilization 10–7 ka BP, another increase after 7 ka BP, and rapid decline to modern values after 3 ka BP. … The amount of heat accumulated by the Earth in the last glacial cycle is a small fraction (<1%) of the heat released due to insolation changes. At the same time, the amount of heat spent on glacier melting is comparable with heat coming due to insolation.
Rosenthal et al., 2017 Here we review proxy records of intermediate water temperatures from sediment cores and corals in the equatorial Pacific and northeastern Atlantic Oceans, spanning 10,000 years beyond the instrumental record. These records suggests that intermediate waters [0-700 m] were 1.5-2°C warmer during the Holocene Thermal Maximum than in the last century. Intermediate water masses cooled by 0.9°C from the Medieval Climate Anomaly to the Little Ice Age. These changes are significantly larger than the temperature anomalies documented in the instrumental record. The implied large perturbations in OHC and Earth’s energy budget are at odds with very small radiative forcing anomalies throughout the Holocene and Common Era. … The records suggest that dynamic processes provide an efficient mechanism to amplify small changes in insolation [surface solar radiation] into relatively large changes in OHC.
Tegzes et al., 2017 The objective of this study was to investigate northward oceanic heat transport in the NwASC [Norwegian Atlantic Slope Current] on longer, geologically meaningful time scales. To this end, we reconstructed variations in the strength of the NwASC over the late-Holocene using the sortable-silt method. We then analysed the statistical relationship between our palaeo-flow reconstructions and published upper-ocean hydrography proxy records from the same location on the mid-Norwegian Margin. Our sortable-silt time series show prominent multi-decadal to multi-centennial variability, but no clear long-term trend over the past 4200 years. … [O]ur findings indicate that variations in the strength of the main branch of the Atlantic Inflow may not necessarily translate into proportional changes in northward oceanic heat transport in the eastern Nordic Seas.
Werner et al., 2017 During the MCA, the contrast between reconstructed summer temperatures over mid- and high-latitudes in Europe and the European/North Atlantic sector of the Arctic shows a very dynamic expression of the Arctic amplification, with leads and lags between continental and more marine and extreme latitude settings. While our analysis shows that the peak MCA [Medieval Climate Anomaly] summer temperatures were as high as in the late 20th and early 21st century, the spatial coherence of extreme years over the last decades seems unprecedented at least back until 750 CE. However, statistical testing could not provide conclusive support of the contemporary warming to supersede the peak of the MCA in terms of the pan-Arctic mean summer temperatures.
Stenni et al., 2017 Within this long-term cooling trend from 0-1900 CE we find that the warmest period occurs between 300 and 1000 CE, and the coldest interval from 1200 to 1900 CE. … A recent effort to characterize Antarctic and sub-Antarctic climate variability during the last 200 years also concluded that most of the trends observed since satellite climate monitoring began in 1979 CE cannot yet be distinguished from natural (unforced) climate variability (Jones et al., 2016), and are of the opposite sign [cooling, not warming] to those produced by most forced climate model simulations over the same post-1979 CE interval. … While changes in the SAM have been related to the human influence on stratospheric ozone and greenhouse gases (Thompson et al., 2011), major gaps remain in identifying the drivers of multi-centennial Antarctic climate variability. For instance, the influence of solar and volcanic forcing on Antarctic climate variability remains unclear. This is due to both the lack of observations and to the lack of confidence in climate model skill for the Antarctic region (Flato et al., 2013). … Our new continental scale reconstructions, based on the extended database, corroborates previously published findings for Antarctica from the PAGES2k Consortium (2013): (1) Temperatures over the Antarctic continent show an overall cooling trend during the period from 0 to 1900CE, which appears strongest in West Antarctica, and (2) no continent-scale warming of Antarctic temperature is evident in the last century.
Mangerud and Svendsen, 2017 Shallow marine molluscs that are today extinct close to Svalbard, because of the cold climate, are found in deposits there dating to the early Holocene. The most warmth-demanding species found, Zirfaea crispata, currently has a northern limit 1000 km farther south, indicating that August temperatures on Svalbard were 6°C warmer at around 10.2–9.2 cal. ka BP, when this species lived there. … After 8.2 cal. ka, the climate around Svalbard warmed again, and although it did not reach the same peak in temperatures as prior to 9 ka, it was nevertheless some 4°C warmer than present between 8.2 and 6 cal. ka BP. Thereafter, a gradual cooling brought temperatures to the present level at about 4.5 cal. ka BP. The warm early-Holocene climate around Svalbard was driven primarily by higher insolation and greater influx of warm Atlantic Water, but feedback processes further influenced the regional climate.
Zhang et al., 2017 [S]ummer temperature variability at the QTP [Qinghai-Tibetan Plateau] responds rapidly to solar irradiance changes in the late Holocene.
Albot, 2017 “Growing paleoclimatic evidence suggests that the climatic signals of Medieval Warm Period and the Little Ice Age events can be detected around the world (Mayewski et al., 2004; Bertler et al., 2011). … [T]he causes for these events are still debated between changes in solar output, increased volcanic activity, shifts in zonal wind distribution, and changes in the meridional overturning circulation (Crowley, 2000; Hunt, 2006).”
Kawahata et al., 2017 The SST [sea surface temperature] shows a broad maximum (~17.3 °C) in the mid-Holocene (5-7 cal kyr BP), which corresponds to the Jomon transgression. … The SST maximum continued for only a century and then the SST dropped by 3.5 °C [15.1 to 11.6 °C] within two centuries. Several peaks fluctuate by 2°C over a few centuries.
Wu et al., 2017 The existence of depressed MAAT [mean annual temperatures] (1.3°C lower than the 3200-year average) between 1480 CE and 1860 CE (470–90 cal. yr BP) may reflect the manifestation of the ‘Little Ice Age’ (LIA) in southern Costa Rica. Evidence of low-latitude cooling and drought during the ‘LIA’ has been documented at several sites in the circum-Caribbean and from the tropical Andes, where ice cores suggest marked cooling between 1400 CE and 1900 CE. Lake and marine records recovered from study sites in the southern hemisphere also indicate the occurrence of ‘LIA’ cooling. High atmospheric aerosol concentrations, resulting from several large volcanic eruptions and sea-ice/ocean feedbacks, have been implicated as the drivers responsible for the ‘LIA’. [Modern temperatures not significantly different than the LIA.]
Li et al., 2017 Contrary to the often-documented warming trend over the past few centuries, but consistent with temperature record from the northern Tibetan Plateau, our data show a gradual decreasing trend of 0.3 °C in mean annual air temperature from 1750 to 1970 CE. This result suggests a gradual cooling trend in some high altitude regions over this interval, which could provide a new explanation for the observed decreasing Asian summer monsoon. In addition, our data indicate an abruptly increased interannual-to decadal-scale temperature variations of 0.8 – 2.2 °C after 1970 CE, in terms of both magnitude and frequency, indicating that the climate system in high altitude regions would become more unstable under current global warming.
Nazarova et al., 2017 The application of transfer functions resulted in reconstructed T July fluctuations of approximately 3 °C over the last 2800 years. Low temperatures (11.0-12.0 °C) were reconstructed for the periods between ca 1700 and 1500 cal yr BP (corresponding to the Kofun cold stage) and between ca 1200 and 150 cal yr BP (partly corresponding to the Little Ice Age [LIA]). Warm periods (modern T[emperatures] July or higher) were reconstructed for the periods between ca 2700 and 1800 cal yr BP, 1500 and 1300 cal yr BP and after 150 cal yr BP.
Thienemann et al., 2017 [P]roxy-inferred annual MATs[annual mean air temperatures] show the lowest value at 11,510 yr BP (7.6°C). Subsequently, temperatures rise to 10.7°C at 9540 yr BP followed by an overall decline of about 2.5°C until present (8.3°C).
Wu et al., 2017 The alkenone-based SST reconstruction shows rapid warming in the first 1500 years of the Holocene … an increase of sea surface temperature from c. 23.0 °C to 27.0 °C, associated with a strengthened summer monsoon from c. 10,350 to 8900 cal. years BP. This was also a period of rapid sea-level rise and marine transgression, during which the sea inundated the palaeo-incised channel … In these 1500 years, fluvial discharge was strong and concentrated within the channel, and the high sedimentation rate (11.8 mm/yr [1.18 m per century]) was very close to the rate of sea-level rise.
Reid, 2017 The small increase in global average temperature observed over the last 166 years is the random variation of a centrally biased random walk. It is a red noise fluctuation. It is not significant, it is not a trend and it is not likely to continue.
Pendea et al., 2017 The Holocene Thermal Maximum (HTM) was a relatively warm period that is commonly associated with the orbitally forced Holocene maximum summer insolation (e.g., Berger, 1978; Bartlein et al., 2011). Its timing varies widely from region to region but is generally detected in paleorecords between 11 and 5 cal ka BP (e.g., Kaufman et al., 2004; Bartlein et al., 2011; Renssen et al., 2012). … In Kamchatka, the timing of the HTM varies. Dirksen et al. (2013) find warmer-than-present conditions between 9000 and 5000 cal yr BP in central Kamchatka [Russia] and between 7000 and 5800 cal yr BP at coastal sites.
Stivrins et al., 2017 Using a multi-proxy approach, we studied the dynamics of thermokarst characteristics in western Latvia, where thermokarst occurred exceptionally late at the Holocene Thermal Maximum. … [A] thermokarst active phase … began 8500 cal. yr BP and lasted at least until 7400 cal. yr BP. Given that thermokarst arise when the mean summer air temperature gradually increased ca. 2°C beyond the modern day temperature, we can argue that before that point, the local geomorphological conditions at the study site must have been exceptional to secure ice-block from the surficial landscape transformation and environmental processes.
Bañuls-Cardona et al., 2017 During the Middle Holocene we detect important climatic events. From 7000 to 6800 [years before present] (MIR 23 and MIR22), we register climatic characteristics that could be related to the end of the African Humid Period, namely an increase in temperatures and a progressive reduction in arboreal cover as a result of a decrease in precipitation. The temperatures exceeded current levels by 1°C [Spain], especially in MIR23, where the most highly represented taxon is a thermo-Mediterranean species, M. (T.) duodecimcostatus.
Åkesson et al., 2017 Reconstructions for southern Norway based on pollen and chironomids suggest that summer temperatures were up to 2 °C higher than present in the period between 8000 and 4000 BP, when solar insolation was higher (Nesje and Dahl, 1991; Bjune et al., 2005; Velle et al., 2005a).
Sugden et al., 2017 [T]he interior Antarctic continent had summers warm enough for tundra vegetation to grow and for mountain glaciers to consist of ice at the pressure melting point.
(press release) Central parts of Antarctica’s ice sheet have been stable for millions of years, from a time when conditions were considerably warmer than now, research suggests. By mapping and analysing surface rocks—including measuring their exposure to cosmic rays – researchers calculated that the mountains have been shaped by an ice sheet over a million-year period, beginning in a climate some 20C warmer than at present. … The last time such climates existed in the mountains of Antarctica was 14 million years ago when vegetation grew in the mountains and beetles thrived. Antarctica’s climate at the time would be similar to that of modern day Patagonia or Greenland.
Abrupt, Degrees-Per-Decade Natural Global Warming (D-O Events) (4)
Sánchez et al., 2017 The estimated increases in Greenland atmospheric temperature were 5–16°C [Capron et al., 2010] and the duration of the warming events between 10 to 200 years [Steffensen et al., 2008].
Lynch-Stieglitz, 2017 Abrupt changes in climate have occurred in many locations around the globe over the last glacial cycle, with pronounced temperature swings on timescales of decades or less in the North Atlantic. The global pattern of these changes suggests that they reflect variability in the Atlantic meridional overturning circulation (AMOC). … In many locations in the Northern Hemisphere, abrupt changes in climate have occurred that span almost the full range of glacial to interglacial conditions, with the transition between climate states occurring in decades or less (Alley & Clark 1999, Voelker 2002). These abrupt climate changes are most clearly recorded in the climate records from glacial ice on Greenland (Andersen et al. 2004) and are referred to as DansgaardOeschger (D-O) events. The warm intervals are referred to as interstadials, and the cold intervals are referred to as stadials. … [T]he prevailing paradigm is that the abrupt climate changes are a result of changes in the northward transport of heat by the Atlantic meridional overturning circulation (AMOC) (Broecker et al. 1985, Clark et al. 2002, Rahmstorf 2002).
Ivanovic et al., 2017 During the Last Glacial Maximum 26–19 thousand years ago (ka), a vast ice sheet stretched over North America [Clark et al., 2009]. In subsequent millennia, as climate warmed and this ice sheet decayed, large volumes of meltwater flooded to the oceans [Tarasov and Peltier, 2006; Wickert, 2016]. This period, known as the “last deglaciation,” included episodes of abrupt climate change, such as the Bølling warming [~14.7–14.5 ka], when Northern Hemisphere temperatures increased by 4–5°C in just a few decades [Lea et al., 2003; Buizert et al., 2014], coinciding with a 12–22 m sea level rise in less than 340 years [5.3 meters per century] (Meltwater Pulse 1a (MWP1a)) [Deschamps et al., 2012].
Markle et al., 2017 The temperature relationship between the hemispheres is commonly attributed to an interhemispheric redistribution of heat by the ocean overturning circulation. Changes in ocean heat transport should be accompanied by changes in atmospheric circulation to satisfy global energy budget constraints. Although changes in tropical atmospheric circulation linked to abrupt events in the Northern Hemisphere are well documented, evidence for predicted changes in the Southern Hemisphere’s atmospheric circulation during Dansgaard–Oeschger cycles is lacking. Here we use a high-resolution deuterium-excess record from West Antarctica to show that the latitude of the mean moisture source for Antarctic precipitation changed in phase with abrupt shifts in Northern Hemisphere climate, and significantly before Antarctic temperature change. This provides direct evidence that Southern Hemisphere mid-latitude storm tracks shifted within decades of abrupt changes in the North Atlantic, in parallel with meridional migrations of the intertropical convergence zone. We conclude that both oceanic and atmospheric processes, operating on different timescales, link the hemispheres during abrupt climate change.
A Model-Defying Cryosphere, Polar Ice (18)
Årthun et al., 2017 Statistical regression models show that a significant part of northern climate variability thus can be skillfully predicted up to a decade in advance based on the state of the ocean. Particularly, we predict that Norwegian air temperature will decrease over the coming years, although staying above the long-term (1981–2010) average. Winter Arctic sea ice extent will remain low but with a general increase towards 2020.
Comiso et al., 2017 The Antarctic sea ice extent has been slowly increasing contrary to expected trends due to global warming and results from coupled climate models. After a record high extent in 2012 the extent was even higher in 2014 when the magnitude exceeded 20 × 106 km2 for the first time during the satellite era. … [T]he trend in sea ice cover is strongly influenced by the trend in surface temperature [cooling]. … A case study comparing the record high in 2014 with a relatively low ice extent in 2015 also shows strong sensitivity to changes in surface temperature. The results suggest that the positive trend is a consequence of the spatial variability of global trends in surface temperature and that the ability of current climate models to forecast sea ice trend can be improved through better performance in reproducing observed surface temperatures in the Antarctic region.
Baggett and Lee, 2017 The dynamical mechanisms that lead to wintertime Arctic warming during the planetary-scale wave (PSW) and synoptic-scale wave (SSW) life cycles are identified by performing a composite analysis of ERA-Interim reanalysis data. The PSW life cycle is preceded by localized tropical convection over the Western Pacific. Upon reaching the mid-latitudes, the PSWs amplify as they undergo baroclinic conversion and constructively interfere with the climatological stationary waves. The PSWs [natural planetary scale waves] flux large quantities of sensible and latent heat into the Arctic which produces a regionally enhanced greenhouse effect that increases downward IR and warms the Arctic two-meter temperature. The SSW life cycle is also capable of increasing downward IR and warming the Arctic two-meter temperature, but the greatest warming is accomplished in the subset of SSW events with the most amplified PSWs. Consequently, during both the PSW and SSW life cycles, wintertime Arctic warming arises from the amplification of the PSWs [natural planetary scale waves].
Ding et al., 2017 The Arctic has seen rapid sea-ice decline in the past three decades, whilst warming at about twice the global average rate. … Internal variability dominates the Arctic summer circulation trend and may be responsible for about 30–50% of the overall decline in September sea ice since 1979.
(press release) [A] substantial chunk of summer sea ice loss in recent decades was due to natural variability in the atmosphere over the Arctic Ocean.
Fernandoy et al., 2017 The firn stable isotope composition reveals that the near–surface temperature at the Antarctic Peninsula shows a decreasing trend (−0.33 °C y−1) between 2008 and 2014.
Thomas et al., 2017 The central Antarctic sites lack coherency and are either not representing regional precipitation or indicate the models inability to capture relevant precipitation processes in the cold, dry central plateau. The drivers of precipitation are reviewed for each region and the temporal variability and trends evaluated over the past 100, 200 and 1000 years. Our study suggests an overall increase in SMB [surface mass balance] across the grounded Antarctic ice sheet of ~ 44 GT since 1800 AD, with the largest (area-weighted) contribution from the Antarctic Peninsula (AP).
Goel et al., 2017 Ice rises are a useful resource to investigate evolution and past climate of the DML coastal region. We investigate Blåskimen Island ice rise, one of the larger isle-type ice rises at the calving front of the intersection of Fimbul and Jelbart Ice Shelves, using geophysical methods. … Using the Input-Output method for a range of parameters and column setups, we conclude that Blåskimen Island has been thickening over the past nine years [2005-2014]. Thickening rates cannot be determined precisely, but ensemble results show that thickening rate averaged over the ice rise varies between 0.07 m a−1 and 0.35 m a−1 [per year]. On longer timescales, we speculate that the summit of Blåskimen Island has been stable within several kilometers at least in the past ∼600 years but no longer than several millennia.
Kim et al., 2017 Understanding the Mechanism of Arctic Amplification and Sea Ice Loss … Sea ice reduction is accelerating in the Barents and Kara Seas. Several mechanisms are proposed to explain the accelerated loss of polar sea ice, which remains an open question. [CO2 is not mentioned anywhere in the paper as a mechanism responsible for Arctic amplification or sea ice loss.]
Oliva et al., 2017 However, a recent analysis (Turner et al., 2016) has shown that the regionally stacked temperature record for the last three decades has shifted from a warming trend of 0.32 °C/decade during 1979–1997 to a cooling trend of − 0.47 °C/decade during 1999–2014. … This recent cooling has already impacted the cryosphere in the northern AP [Antarctic Peninsula], including slow-down of glacier recession, a shift to surface mass gains of the peripheral glacier and a thinning of the active layer of permafrost in northern AP islands.
Martín-Español et al., 2017 We investigate the mass balance of East Antarctica for 2003–2013 using a Bayesian statistical framework. … We apportion mass trends to SMB and ice dynamics for the EAIS, based on two different assumptions, different remote sensing data and two RCMs. In the first experiment, the model apportions about a third of the mass trend to ice dynamics, +17 Gt/yr, and two thirds, +40 Gt yr−1 to SMB, resulting in a total mass trend for the EAIS [East Antarctic Ice Sheet] of +57 ± 20 Gt yr−1.
Pittard et al., 2017 We suggest the Lambert-Amery glacial system will remain stable, or gain ice mass and mitigate a portion of potential future sea level rise over the next 500 years, with a range of +3.6 to -117.5 mm GMSL-equivalent.
Fettweis et al ., 2017 Results from all MAR simulations indicate that (i) the period 1961–1990, commonly chosen as a stable reference period for Greenland SMB and ice dynamics, is actually a period of anomalously positive SMB (∼ +40 Gt yr−1 ) compared to 1900–2010 … [T]he ERA-20C forced simulation suggests that SMB [surface mass balance] during the 1920–1930 warm period over Greenland was comparable to the SMB of the 2000s, due to both higher melt and lower precipitation than normal. … The period 1961–1990 has been considered as a period when the total mass balance of the Greenland ice sheet was stable (Rignot and Kanagaratnam, 2006) and near zero. However, at the last century scale, all MAR reconstructions suggest that SMB [surface mass balance] was particularly positive during this period [1961-1990] (SMB was most positive from the 1970s to the middle of the 1990s), suggesting that mass gain may well have occurred during this period, in agreement with results from Colgan et al. (2015). Finally, with respect to the 1961–1990 period, the integrated contribution of the GrIS SMB anomalies over 1900–2010 is a sea level rise of about 15 ± 5 mm [1.35 cm per century], with a null contribution from the 1940s to the 2000s, suggesting that the recent contribution of GrIS to sea level change (van den Broeke et al., 2016) is unprecedented in the last century.
Reeves Eyre and Zeng, 2017 Ice sheet-average annual mean SAT [surface air temperatures] from different datasets are highly correlated in recent decades, but their 1901–2000 trends differ even in sign [Greenland cooled]. Compared with the MERRA2 climatology combined with gridded SAT analysis anomalies, thirty-one earth system model historical runs from the CMIP5 archive [biases] reach ~5°C for the 1901–2000 average bias and have opposite trends [modeled warming when Greenland was cooling] for a number of sub-periods. … Due to its remoteness and extreme climate however, continuous widespread climate monitoring over the GrIS has been carried out for only about the last two decades, and even then with rather sparse coverage in some geographic areas and glaciological regimes. … Box (2002) found a pattern of warming from ~1900 to ~1940, cooling from ~1940 to ~1990, and warming from ~1990 onwards. In addition, inter-annual variability was found to be closely related to the North Atlantic Oscillation (NAO). …Biases vary by season and by region of the ice sheet: in the ablation region (demarcated here by the 1500 m elevation contour) during summer, most reanalyses have a ~1°C positive bias (though 20CR and ERA–20C have negative biases) while CRU and Berkeley Earth gridded SAT analyses have larger positive biases.
van der Bilt et al., 2017 [R]econstruction of glacier variations over the past ∼1250 years. Together with local moraine evidence and supporting evidence from other Southern Hemisphere glaciers on New Zealand and in Patagonia, our findings reveal a series of consecutively diminishing Late Holocene advances. In addition to a glacier maximum before 1250 cal a BP, these include a two-stage Little Ice Age with advances around 300 and 120 cal a BP, in line with evidence from southern Patagonia. In addition, we present evidence for an unreported [glacier] retreat behind present limits around 500 cal BP.
Fogt et al., 2017 At their peak on 6 December 1911, the temperatures measured by Amundsen exceeded -16°C, which represents an anomaly relative to our estimate from ERA-Int climatology [long-term temperature and pressure record] of more than 10°C. … Amundsen’s sledging temperature measurements during this time are much warmer than the hourly and daily mean observations collected at the South Pole station since 1957, even when accounting for the average differences in temperature between Amundsen’s location and the South Pole, which is often colder than nearby areas due to pooling of cold air in the slightly lower elevation (Comiso 2000). The daily mean temperature measured at the South Pole on December 7, 2015 of -19.8°C (max hourly temperature of -18.2°C) is the only comparable warm day before December 11th, otherwise observed South Pole daily mean temperatures have never exceeded -20°C in this portion of early summer [since 1911]. … [D]aily maximum temperatures above -20°C occurred for two consecutive days in 2015 and 2012, but these are quite warm exceptions to the normal conditions (Fig. S9). In contrast, Amundsen experienced four continuous days with daily mean temperatures exceeding -19.0°C and temperature anomalies from the ERA-Int climatology greater than 10°C. … Notably, there is a large positive spike during summer 1911/12, when seasonal mean pressures rise above 1000 hPa. The reconstruction pre-1957 shows only one other summer with pressures above 1000 hPa, in 1925/26, as discussed in Fogt et al. (2016b), while the direct observations display one summer in 1976/77 when they exceed 1000 hPa. This ranks the McMurdo pressure during the summer of the South Pole races [summer 1911/12] in the top three highest over the last 110 years. … Scott’s absolute difference of 19.58°C and anomaly difference of 12.58°C clearly stand out as unique: in only one year during 1979-2015 was there a similar large swing in temperatures on these days.
Schroeter et al., 2017 Antarctic sea ice extent has increased by approximately 1.5 % per decade since satellite observations began in 1979 (Parkinson and Cavalieri, 2012; Turner et al., 2015). The small overall increase masks higher-magnitude regional and seasonal trends around the continent, most notably an increase of 3.9 % per decade in the Ross Sea peaking during spring, and a decrease of −3.4 % per decade in the Amundsen and Bellingshausen seas peaking during autumn (Turner et al., 2015). By contrast, models in the Coupled Model Intercomparison Project Phase 5 (CMIP5) exhibit decreasing sea ice trends in all months (Turner et al., 2013a). The reasons for the disparity between observed and modelled trends are not yet well understood (Bindoff et al., 2013; Hobbs et al., 2016).
Bolch et al., 2017 Previous geodetic estimates of mass changes in the Karakoram revealed balanced budgets or a possible slight mass gain since ∼ 2000. Indications of longer-term stability exist but only very few mass budget analyses are available before 2000. Here, based on 1973 Hexagon KH-9, ∼ 2009 ASTER and the SRTM DTM, we show that glaciers in the Hunza River basin (central Karakoram) were on average in balance or showed slight insignificant mass loss within the period ∼ 1973–2009.
Gagné et al., 2017 Updated observational datasets without climatological infilling show that there was an increase in sea ice concentration in the Eastern Arctic between 1950 and 1975, contrary to earlier climatology in-filled observational datasets that show weak inter-annual variations during that time period.
Recent Cooling In The North Atlantic
Yeager and Robson, 2017 [W]hile the late twentieth century Atlantic was dominated by NAO-driven THC [thermohaline circulation] variability, other mechanisms may dominate in other time periods. … More recently, the SPNA [sub polar North Atlantic] upper ocean has again been cooling, which is also thought to be related to a slowdown in the THC. A continued near-term cooling of the SPNA has been forecast by a number of prediction systems, with implications for pan-Atlantic climate.