Part 3. Natural Climate Change Observation, Reconstruction
Lack Of Anthropogenic/CO2 Signal In Sea Level Rise (9)
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
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.
No Net Warming During 20th (21st) Century (10)
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).
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).
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.
A Warmer Past/Non-Hockey Stick Reconstructions (21)
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.
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).
Abrupt, Degrees-Per-Decade Natural Global Warming (D-O Events) (1)
A Model-Defying Cryosphere, Polar Ice (10)
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).
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.