Part 1. Natural Climate Change Observation, Reconstruction
Warming Since Mid/Late 20th Century?
A Warmer Past: Non-Hockey Stick Reconstructions
Lack Of Anthropogenic/CO2 Signal In Sea Level Rise
Sea Levels Multiple Meters Higher 4,000-7,000 Years Ago
A Model-Defying Cryosphere, Polar Ice
Mass Extinction Events Caused By Glaciation, Sea Level Fall
Antarctic Ice Melting In High Geothermal Heat Flux Areas
Abrupt, Degrees-Per-Decade Natural Global Warming
Warming Since The Mid/Late 20th Century?
Lansner and Pepke Pedersen, 2018 In locations best sheltered and protected against ocean air influence, the vast majority of thermometers worldwide trends show temperatures in recent decades rather similar to the 1920–1950 period. This indicates that the present-day atmosphere and heat balance over the Earth cannot warm areas – typically valleys – worldwide in good shelter from ocean trends notably more than the atmosphere could in the 1920–1950 period. … [T]he lack of warming in the OAS temperature trends after 1950 should be considered when evaluating the climatic effects of changes in the Earth’s atmospheric trace amounts of greenhouse gasses as well as variations in solar conditions.
Shu et al., 2018 The link between boreal winter cooling over the midlatitudes of Asia and the Barents Oscillation (BO) since the late 1980s is discussed in this study, based on five datasets. Results indicate that there is a large-scale boreal winter cooling during 1990–2015 over the Asian midlatitudes, and that it is a part of the decadal oscillations of long-term surface air temperature (SAT) anomalies.
Partridge et al., 2018 We present a novel approach to characterize the spatiotemporal evolution of regional cooling across the eastern U.S. (commonly called the U.S. warming hole), by defining a spatially explicit boundary around the region of most persistent cooling. The warming hole emerges after a regime shift in 1958 where annual maximum (Tmax) and minimum (Tmin) temperatures decreased by 0.46°C and 0.83°C respectively. … [T]he seasonal modes also vary in causation. Winter temperatures in the warming hole are significantly correlated with the Meridional Circulation Index (MCI), North Atlantic Oscillation (NAO), and Pacific Decadal Oscillation (PDO). … We select only stations in the contiguous U.S. that have an 80% complete record from 1901-2015, resulting in 1407 temperature stations … [W]e note that there is considerable spatial coherence between the location of the summer warming hole and the region within which cooler extreme temperatures are associated with agricultural intensification (Mueller et al. 2015). Multiple studies have demonstrated that irrigation can have a significant influence on regional precipitation and can lead to cooler temperatures both locally through increased evapotranspiration, and downwind of the irrigated region through enhanced moisture transport (Alter et al., 2015; Bonfils & Lobell, 2007; Pei et al., 2014, 2016).
Westergaard-Nielsen et al., 2018 Here we quantify trends in satellite-derived land surface temperatures and modelled air temperatures, validated against observations, across the entire ice-free Greenland. … Warming trends observed from 1986–2016 across the ice-free Greenland is mainly related to warming in the 1990’s. The most recent and detailed trends based on MODIS (2001–2015) shows contrasting trends across Greenland, and if any general trend it is mostly a cooling. The MODIS dataset provides a unique detailed picture of spatiotemporally distributed changes during the last 15 years. … Figure 3 shows that on an annual basis, less than 36% of the ice-free Greenland has experienced a significant trend and, if any, a cooling is observed during the last 15 years (<0.15 °C change per year).
Eck, 2018 [A] majority (12/14) of the regions within the SAM [Southern Appalachian Mountains] have experienced a long-term decline in mean winter temperatures since 1910. Even after removing the highly anomalous 2009-2010 winter season, which was more than two standard deviations away from the long-term mean, the cooling of mean winter temperatures is still evident. … Higher winter temperatures dominated the early 20th century in the SAM [Southern Appalachian Mountains] with nine of the ten warmest winter seasons on record in the region having occurred before 1960. The 1931-1932 winter season, the warmest on record, averaged 8.0°C for DJF, nearly 4.7°C higher than the 1987-2017 normal mean winter temperature of 3.3°C. … Despite the 2016-2017 winter season finishing with the highest mean temperatures (5.7ºC) observed in the SAM [Southern Appalachian Mountains] since 1956-1957, there have been several years of anomalous negative temperature anomalies, with the 2009-2010 (0.3ºC) and 2010-2011 (1.2ºC) winter seasons finishing as two of the coldest on record for all regions.
Yi, 2018 As measures of climate response, temperature and precipitation data from the north, east, and south-facing mountain ranges of Shennongjia Massif in the coldest and hottest months (January and July), different seasons (spring, summer, autumn, and winter) and each year were analyzed from a long-term dataset (1960 to 2003) to tested variations characteristics, temporal and spatial quantitative relationships of climates. The results showed that the average seasonal temperatures and precipitation in the north, east, and south aspects of the mountain ranges changed at different rates. The average seasonal temperatures change rate ranges in the north, east, and south-facing mountain ranges were from –0.0210 ℃/yr to 0.0143 ℃/yr, –0.0166 ℃/yr to 0.0311 ℃/yr, and –0.0290 ℃/yr to 0.0084 ℃/yr, respectively, and seasonal precipitation variation magnitude were from –1.4940 mm/yr to 0.6217 mm/yr, –1.6833 mm/yr to 2.6182 mm/yr, and –0.8567 mm/yr to 1.4077 mm/yr, respectively. The climates variation trend among the three mountain ranges were different in magnitude and direction, showing a complicated change of the climates in mountain ranges and some inconsistency with general trends in global climate change.
Nicolle et al., 2018 Persistent multidecadal variability with a period of 50– 90 years is consistent between the subarctic North Atlantic mean record and the AMO over the last 2 centuries (AD 1856–2000). … The climate of the Arctic–subarctic is influenced by the Atlantic and the Pacific oceans, which experience internal variability on different timescales with specific regional climate impacts. In the North Atlantic sector, instrumental sea surface temperature (SST) variations since AD 1860 highlight low-frequency oscillations known as the AMO (Kerr, 2000). … The evidence of industrial era warming starting earlier at the beginning of the 19th century was proposed by Abram et al. (2016) for the entire Arctic area. However, the intense volcanic activity of the 19th century (1809, 1815 and around 1840; Sigl et al., 2015) may also explain the apparent early warming trend, suggesting that it may have been recovery from an exceptionally cool phase. On the scale of the Holocene, internal fluctuations occurring on a millennial scale have been identified in the subarctic North Atlantic area and were tentatively related to ocean dynamics (Debret et al., 2007; Mjell et al., 2015). … The LIA is, however, characterized by an important spatial and temporal variability, particularly visible on a more regional scale (e.g., PAGES 2k Consortium, 2013). It has been attributed to a combination of natural external forcings (solar activity and large volcanic eruptions) and internal sea ice and ocean feedback, which fostered long-standing effects of short-lived volcanic events (Miller et al., 2012).
Purich et al., 2018 Observed Southern Ocean changes over recent decades include a surface freshening (Durack and Wijffels 2010; Durack et al. 2012; de Lavergne et al. 2014), surface cooling (Fan et al. 2014; Marshall et al. 2014; Armour et al. 2016; Purich et al. 2016a) and circumpolar increase in Antarctic sea ice (Cavalieri and Parkinson 2008; Comiso and Nishio 2008; Parkinson and Cavalieri 2012). … [A]s high-latitude surface freshening is associated with surface cooling and a sea ice increase, this may be another factor contributing to the CMIP5 models excessive Southern Ocean surface warming contrasting the observed surface cooling (Marshall et al. 2014; Purich et al. 2016a), and sea ice decline contrasting the observed increases (Mahlstein et al. 2013; Polvani and Smith 2013; Swart and Fyfe 2013; Turner et al. 2013; Zunz et al. 2013; Gagne et al. 2015) over recent decades. … Our results suggest that recent multi-decadal trends in large-scale surface salinity over the Southern Ocean have played a role in the observed surface cooling seen in this region. … The majority of CMIP5 models do not simulate a surface cooling and increase in sea ice (Fig. 8b), as seen in observations.
Cerrone and Fusco, 2018 Compelling evidence indicates that the large increase in the SH sea ice, recorded over recent years, arises from the impact of climate modes and their long-term trends. The examination of variability ranging from seasonal to interdecadal scales, and of trends within the climate patterns and total Antarctic sea ice concentration (SIC) for the 32-yr period (1982–2013), is the key focus of this paper. The results herein indicate that a progressive cooling has affected the year-to-year climate of the sub-Antarctic since the 1990s. This feature is found in association with increased positive SAM and SAO phases detected in terms of upward annual and seasonal trends (in autumn and summer) and upward decadal trends. In addition, the SIC [sea ice concentration] shows upward annual, spring, and summer trends, indicating the insulation of Antarctica from the warmer flows in the midlatitudes.
Tang et al., 2018 The study of Antarctic precipitation has attracted a lot of attention recently. The reliability of climate models in simulating Antarctic precipitation, however, is still debatable. This work assess the precipitation and surface air temperature (SAT) of Antarctica (90°S to 60°S) using 49 Coupled Model Intercomparison Project phase 5 (CMIP5) global climate models
Kim et al., 2018 Recent surface cooling in the Yellow and East China Seas and the associated North Pacific climate regime shift … The Yellow and East China Seas (YECS) are widely believed to have experienced robust, basin-scale warming over the last few decades. However, the warming reached a peak in the late 1990s, followed by a significant cooling trend. … The most striking evolution pattern is that a robust warming trend at a rate of +0.40°C per decade reached a peak in the late 1990s, and then it turned downward at a rate of −0.36°C per decade. The positive and then negative trends are estimated throughout the YECS for the periods 1982−1997.
Burger et al., 2018 Previous studies have identified spatial and temporal trends in temperature and precipitation in Chile over recent decades. Temperature rose significantly during the mid to late 20th century in coastal locations between 18 to 33 °S (Rosenblüth et al., 1997), but then started to decrease, with a cooling trend up to -0.20ºC decade-1 dominating over the past 20-30 years (Falvey and Garreaud, 2009).
Ramesh and Soni, 2018 The present paper reviews the progress of India’s scientific research in polar meteorology. The analysis of 25 years meteorological data collected at Maitri station for the period 1991–2015 is presented in the paper. The observed trend in thetemperature data of 19 Antarctic stations obtained from READER project for the period 1991–2015 has also been examined. The 25 years long term temperature record shows cooling over Maitri station. The Maitri station showed cooling of 0.054 °C per year between 1991 and 2015, with similar pronounced seasonal trends. The nearby Russian station Novolazarevskaya also showed a cooling trend of 0.032 °C per year. … The temperature trend in average temperature of 19 Antarctica stations is also examined to ascertain the extent of cooling or warming trend (Supplementary Table_S1). The majority of stations in East Antarctica close to the coast show cooling or no significant trend. … Turner et al. (2016) using stacked temperature record found a significant cooling trend for the Antarctic Peninsula for the period 1999–2014.
Hrbáček et al., 2018 Active layer monitoring in Antarctica: an overview of results from 2006 to 2015 … Air temperatures showed significant regional differences within the study areas. In the western Antarctic Peninsula region, Vestfold Hills and northern Victoria Land, a slight air temperature cooling was detected, while at other sites in Victoria Land and East Antarctica the air temperature was more irregular, showing no strong overall trend of warming or cooling during the study period (Figure 2). The Antarctic Peninsula region has been reported as the most rapidly warming part of Antarctica (e.g. Turner et al., 2005, 2014), but cooling has been reported since 2000 (Turner et al., 2016). Relatively stable air temperature conditions during the past 20 years were reported in Victoria Land (Guglielmin & Cannone, 2012).
Bereiter et al., 2018 Our reconstruction provides unprecedented precision and temporal resolution for the integrated global ocean, in contrast to the depth-, region-, organism- and season-specific estimates provided by other methods. We find that the mean global ocean temperature is closely correlated with Antarctic temperature and has no lead or lag with atmospheric CO2, thereby confirming the important role of Southern Hemisphere climate in global climate trends. We also reveal an enigmatic 700-year warming during the early Younger Dryas period (about 12,000 years ago) that surpasses estimates of modern ocean heat uptake.
(press release) “Our precision is about 0.2 ºC (0.4 ºF) now, and the warming of the past 50 years is only about 0.1 ºC,” he said, adding that advanced equipment can provide more precise measurements, allowing scientists to use this technique to track the current warming trend in the world’s oceans.
Clem et al., 2018 Over the past 60 years [since 1957], the climate of East Antarctica cooled while portions of West Antarctica were among the most rapidly warming regions on the planet. The East Antarctic cooling is attributed to a positive trend in the Southern Annular Mode (SAM) and a strengthening of the westerlies, while West Antarctic warming is tied to zonally asymmetric circulation changes forced by the tropics. [CO2 is not mentioned in the paper as a factor in warming/cooling trends.] This study finds recent (post-1979) surface cooling of East Antarctica during austral autumn to also be tied to tropical forcing, namely, an increase in La Niña events. … The South Atlantic anticyclone is associated with cold air advection, weakened northerlies, and increased sea ice concentrations across the western East Antarctic coast, which has increased the rate of cooling at Novolazarevskaya and Syowa stations after 1979. This enhanced cooling over western East Antarctica is tied more broadly to a zonally asymmetric temperature trend pattern across East Antarctica during autumn that is consistent with a tropically forced Rossby wave rather than a SAM pattern; the positive SAM pattern is associated with ubiquitous cooling across East Antarctica.
Kwon et al., 2018 We monitored 1,378 nests of western sandpipers, semipalmated sandpipers, and red‐necked phalaropes at a subarctic site during 1993–1996 and 2010–2014. … We found an unexpected long‐term cooling trend during the early part of the breeding season. Three species delayed clutch initiation by 5 days in the 2010s relative to the 1990s. … A cooling trend occurred during the prelaying windows of all species, resulting in daily mean temperatures that averaged 4.9, 5.8, and 4.4°C cooler during the 2010s than the 1990s for western sandpiper, semipalmated sandpiper, and red‐necked phalaropes, respectively.
Gervais et al., 2018 Recent studies have documented the development of a warming deficit in North Atlantic sea surface temperatures (SST) both in observations of the current climate (Rahmstorf et al. 2015; Drijfhout et al. 2012) and in future climate simulations (Drijfhout et al. 2012; Marshall et al. 2015; Woollings et al. 2012). This “North Atlantic warming hole” (NAWH) is characterized in the observed record as a region south of Greenland with negative trends in SSTs [cooling] of 0.8 K century-1 (Rahmstorf et al. 2015). In fully coupled global climate model (GCM) future simulations, the NAWH is seen as a significant deficit in warming within the North Atlantic subpolar gyre (Marshall et al. 2015; Winton et al. 2013; Gervais et al. 2016). This local reduction in future warming is communicated to the overlying atmosphere and may impact atmospheric circulation (Gervais et al. 2016), including the North Atlantic storm track (Woollings et al. 2012).
Liu et al., 2018 Plant phenology is an important natural indicator of climate change (Körner and Basler 2010) and a proxy for climate reconstruction (Ge et al. 2008; Zheng et al. 2015; Fang and Chen 2015). … In this paper, we reconstruct a phenological series of the first blooming date of Amygdalus davidiana (FBA) in Beijing from A.D. 1741 to 2000. In these series, phenological records after 1950 are all observational data, and before that are reconstructed data based on the records from diaries, poems and other historical documents. In China, poems and diaries are used as important sources of proxy data for reconstructing historical phenological series (Ge et al. 2008) because many phenological phenomena had been recorded in detail in these historical documents (Chuine et al. 2004; Zhang et al. 2013; Liu et al. 2016). … Based on the average of the FBA series, the original FBA series could be divided into 1 later blooming periods of A.D. 1796–1985 and 2 earlier blooming periods of A.D. 1741–1795 and A.D. 1985–2000. … Approximately 85% of the extreme delays followed the large volcanic eruptions (VEI ≥ 4), as the same proportion of the extreme delays followed El Niño events. About 73% of the extreme delays fall in the valleys of sunspot cycles or the Dalton minimum period in the year or the previous year.
Lei et al.,2018 (N, NE, SE China) The authors analyzed the observed winter surface air temperature in eastern mainland China during the recent global warming hiatus period through 1998-2013. The results suggest a substantial cooling trend of about -1.0°/decade in Eastern China, Northeast China and Southeast China.
Cerrone and Fusco, 2018 (Antarctica) Compelling evidence indicates that the large increase in the SH sea ice, recorded over recent years, arises from the impact of climate modes and their long-term trends. The examination of variability ranging from seasonal to interdecadal scales, and of trends within the climate patterns and total Antarctic sea ice concentration (SIC) for the 32-yr period (1982–2013), is the key focus of this paper. The results herein indicate that a progressive cooling has affected the year-to-year climate of the sub-Antarctic since the 1990s.
Fernandoy et al., 2018 (Antarctic Peninsula) As shown by firn core analysis, the near-surface temperature in the northern-most portion of the Antarctic Peninsula shows a decreasing trend (−0.33°C year−1) between 2008 and 2014 [-1.98°C].
Vignon et al., 2018 (Antarctica) The near‐surface Antarctic atmosphere experienced significant changes during the last decades (Steig et al., 2009; Turner et al., 2006). In particular, the near‐surface air over the Western part of Antarctica exhibits one of the major warming over the globe (Bromwich et al., 2013a), with heating rates larger than 0.5 K per decade at some places. Despite a significant warming in the end of the 20th century, the Antarctic Peninsula has been slightly cooling since 1998, reflecting the high natural variability of the climate in this region (Turner et al., 2016). East Antarctica has experienced a slight cooling trend (Nicolas & Bromwich, 2014; Smith & Polvani, 2017) particularly marked during autumn.
A Warmer Past, Non-Hockey Stick Reconstructions
Li et al., 2018 There are also other studies that suggest that the recent climate warming over the southeastern TP actually began in the 1820s (Shi et al., 2015). However, a few reconstructions from the west and northwest parts of Sichuan or from the southeastern TP indicate that there were no obvious increase of temperature during the past decades (Li et al., 2015b; Zhu et al., 2016).
Yu et al., 2018 Reconstruction results explained 39.3% of climatic variance over the calibration period 1959–2015, and they indicated that the central XiaoXing Anling Mountains have experienced six major warm periods, five major cold periods, and several cold years that coincided with a sequence of major tropical volcanic eruptions. … Power spectrum revealed the existence of significant frequency cycles of variability at 2.0–2.3, 2.5–2.7, 2.9, 3.0, 3.4–4.5, 5.6, 7.2, 7.5–8.0, 8.2, 8.9, 9.9, 10.5–11.5, and 70.5 years, which may be linked to large-scale atmospheric-oceanic variability, such as the El Niño-Southern Oscillation, solar activity, and the Pacific Decadal Oscillation.
Nielsen et al., 2018 The Holocene climatic optimum was a period 8–5 kyr ago when annual mean surface temperatures in Greenland were 2–3°C warmer than present-day values. … We find that the ice sheet retreats to a minimum volume of ∼0.15–1.2 m sea-level equivalent smaller than present in the early or mid-Holocene when forcing an ice-sheet model with temperature reconstructions that contain a climatic optimum, and that the ice sheet has continued to recover from this minimum up to present day. … The initial mass loss in response to the temperature increase in the early Holocene is largest when forcing the ice sheet with the temperature and accumulation reconstructions from Gkinis and others (2014) (Experiment 5). In this simulation, temperature anomalies peak at more than 5°C above the present-day reference climate in the early Holocene and the ice sheet loses 20% of its volume in the 3000 years following the onset of the Holocene through increased surface melting. … The largest and most rapid retreat of the ice sheet was found for Experiment 5, which was forced by the temperature and accumulation reconstructions of Gkinis and others (2014). In this temperature reconstruction, temperature increases rapidly at the onset of the interglacial and has several shorter periods with temperatures more than 5°C above present in the early Holocene. .. Geological evidence suggests further that the ice-sheet margins in the southwest retreated up to ∼ 100km behind their present-day position during the mid-Holocene (Funder and others, 2011). This evidence is further supported by interpretations of relative sea-level records and bedrock uplift rates that also point towards ice sheet retreat beyond the present ice volume in the mid-Holocene (Khan and others, 2008; Funder and others, 2011; Lecavalier and others, 2014).
Anderson et al., 2018 We estimate that air temperatures were 2.5–3.0 °C higher during the Holocene Thermal Maximum than the local 1960–1990 average. … Between 1700 and 1925 CE temperatures were likely 0.6–0.8 °C lower than the 1950–2015 reference temperature.
Harning et al., 2018 Iceland’s terrestrial HTM [Holocene Thermal Maximum] has previously been constrained to ~7.9 to 5.5 ka based on qualitative lake sediment proxies (Larsen et al., 2012; Geirsdottir et al., 2013), likely in association with progressive strengthening and warming of the Irminger Current (Castaneda et al., 2004; Smith et al., 2005; Olafsdottir et al., 2010). Numerical modeling experiments for Drangajokull suggest that peak air temperatures were 2.5 – 3°C warmer at this time relative to the 1961-1990 CE average (Anderson et al., 2018). … During the Little Ice Age (LIA, 1250-1850 CE), the Vestfirðir region entered the lowest multi centennial spring/summer temperature anomalies of the last 9 ka. Based on recent numerical modeling simulations, this anomaly is estimated to be 0.6-0.8°C below the 1950-2015 average on Vestfirðir (Anderson et al., 2018).
Grieman et al., 2018 [C]limate anomalies appear to be reflected in the Tunu VA [vanillic acid] record, with elevated VA [vanillic acid] during the warm periods and lower levels during the colder periods. The data suggest a positive correlation between North American fire and hemispheric mean temperature. This relationship could be due to climate-driven changes in temperature or precipitation on burning extent, frequency, or location, as well as to changes in atmospheric transport patterns. … … [E]levated VA [vanillic acid] early in the record [Roman Warm Period] and around the MCA [Medieval Climate Anomaly]. It also emphasizes the decreasing trend from 1200-1900 CE [Little Ice Age] and the increase during the 20th century [Current Warm Period].
McGowan et al., 2018 Our reconstructed Tmax [temperature maximum] for these warmer conditions peaks around 1390 CE at + 0.8 °C above the 1961–90 mean, similar to the peak Tmax during the RWP [Roman Warm Period]. These results are aligned with the findings that show the period from 1150 to 1350 CE to be the warmest pre-industrial chronzone of the past 1000 yrs for southeast Australia.
Allen et al., 2018 The longest sustained period of relatively high temperatures in the reconstructions is the post 1950 CE period although there are clearly individual years much earlier that were warmer than any in the post-1950 period.
Polovodova Asteman et al., 2018 The record demonstrates a warming during the Roman Warm Period (~350 BCE – 450 CE), variable bottom water temperatures during the Dark Ages (~450 – 850 CE), positive bottom water temperature anomalies during the Viking Age/Medieval Climate Anomaly (~850 – 1350 CE) and a long-term cooling with distinct multidecadal variability during the Little Ice Age (~1350 – 1850 CE). The fjord BWT [bottom water temperatures, Western Sweden] record also picks up the contemporary warming of the 20th century, which does not stand out in the 2500-year perspective and is of the same magnitude as the Roman Warm Period and the Medieval Climate Anomaly.
Hanna et al., 2018 Here, we utilize one such sediment archive from Simpson Lagoon, Alaska, located adjacent to the Colville River Delta to reconstruct temperature variability and fluctuations in sediment sourcing over the past 1700 years. Quantitative reconstructions of summer air temperature […] reveal temperature departures correlative with noted climate events (i.e. ‘Little Ice Age’, ‘Medieval Climate Anomaly’). … Reconstructed temperatures are generally coolest between 300 and 800 CE (Tavg = 2.24 ± 0.98°C), displaying three temperature minima centered at 410 CE (1.34 ± 0.72°C), 545 CE (1.91 ± 0.69°C), and 705 CE (1.49 ± 0.69°C). Temperatures then rapidly increased, reaching the warmest interval (800–1000 CE) in the approximately 1700-year record. During this interval, average temperatures were 3.31 ± 0.65°C, with a maximum temperature of 3.98°C.
Wang et al., 2018 The average RAN15-MAAT of 18.4°C over the most recent part of the record (<0.8 ka BP) [the last 800 years BP] overlaps with the range of MAATs, ca. 16.2°C to 18.7°C (av. 17.5°C) measured since 1952 at the nearest meteorological station (Yichang, located ca. 100 km away) and is very close to the av. MAAT of 18°C measured directly outside the cave by a temperature logger between 2004 and 2007 (Hu et al., 2008a). This agreement between reconstructed temperatures and instrumental measurements increases our confidence in the potential of the RAN15 proxy. RAN15-MAATs in HS4 vary from 16.5°C to 20.6°C (av. 19°C), during the last 9 ka BP, and broadly follow a long-term trend of declining temperatures in line with declining solar insolation at 30°N in July (Laskar et al., 2004) (Fig. 4B). The temperature variation (4.1°C) in our record is larger than the calibration error of the RAN15 proxy (RMSE ¼ 2.6°C; Wang et al., 2016). … The Holocene Climate Optimum (HCO) shown in the RAN15-MAAT record is from 8 to 6 ka BP, with the highest temperature at ca. 7.0 ka BP. Superimposed on the orbital-scale Holocene trend are centennial to millennial scale climate fluctuations of ca. 1-2°C. Interestingly, the most recent 0.9 ka BP [900 years BP] is distinguished by greater variability with the highest (20.5°C) and lowest (16.5°C) RAN15-MAATs occurring consecutively at 0.6 ka BP [600 years BP] and 0.5 ka BP [500 years BP]. [Surface temperatures dropped by -4.0°C within ~100 years.]
Zheng et al., 2018 In this study we present a detailed GDGT data set covering the last 13,000 years from a peat sequence in the Changbai Mountain in NE China. The brGDGT-based temperature reconstruction from Gushantun peat indicates that mean annual air temperatures in NE China during the early Holocene were 5–7°C higher than today. Furthermore, MAAT records from the Chinese Loess Plateau also suggested temperature maxima 7–9°C higher than modern during the early Holocene (Peterse et al., 2014; Gao et al., 2012; Jia et al., 2013). Consequently, we consider the temperatures obtained using the global peat calibration to be representative of climate in (NE) China. … The highest temperatures occurred between ca. 8 and 6.8 kyr BP, with occasional annual mean temperatures >8.0 ± 4.7°C, compared to the modern-day MAAT of ∼3°C.
Levy et al., 2018 The three historical moraine crests indicate that there were at least three ice-margin stillstands or advances during historical time. Summer temperature records from North lake (Axford et al. 2013) and Lake N3 (Thomas et al. 2016) broadly register cooling in the past 200 years in western Greenland, which likely influenced the advance to the historical moraines.
Perner et al., 2018 From c. 1.5 ka BP onwards, we record a prominent subsurface cooling and continued occurrence of fresh and sea‐ice loaded surface waters at the study site.
Lemmen and Lacourse, 2018 The early Holocene was marked by relatively stable temperatures that exceeded modern by ~2 to 3°C. Inferred temperatures generally decrease through the remainder of the Holocene.
Magyari et al., 2018 [I]ts climatic tolerance limits were used to infer July mean temperatures exceeding modern values by 2.8°C at this time [8200-6700 cal yr BP] (Magyari et al., 2012).
Fan et al., 2018 The thermocline water temperature variabilities of the two sites, in particular the highest peaks at ~7 ka BP, are different from the records of the open western Pacific. Reoccurrence of the South China Sea Throughflow and thus a decreased surface throughflow along the Makassar Strait perhaps led to a warmer peak of thermocline temperature at ~7 ka BP than at ~11 ka BP.
Blundell et al., 2018 Energy carried by warm tropical water, transported via the Atlantic Meridional Overturning Circulation (AMOC), plays a vital role in regulating the climate of regions bordering the North Atlantic Ocean. Previous phases of elevated freshwater input to areas of North Atlantic Deep Water (NADW) production in the early to mid-Holocene have been linked with slow-downs in the AMOC and changes in regional climate.
Badino et al., 2018 Between ca. 8.4-4 ka cal BP [8,400 to 4,000 years before present], our site [Italian Alps] experienced a mean TJuly of ca. 12.4 °C, i.e. 3.1 °C warmer than today [9.3 °C]. … Between 7400 and 3600 yrs cal BP, an higher-than-today forest line position persisted under favorable growing conditions (i.e. TJuly at ca. 12 °C).
Papadomanolaki et al., 2018 (Baltic Sea) A large fraction of the Baltic Proper became hypoxic again between 1.4 and 0.7 ka BP, during the Medieval Climate Anomaly (MCA), when mean air temperatures were 0.9–1.4 °C higher than temperatures recorded in the period 1961–1990 (e.g. Mann et al., 2009; Jilbert and Slomp, 2013).
Leonard et al., 2018 (Great Barrier Reef, Australia) Coral derived sea surface temperature (SST-Sr/Ca) reconstructions demonstrate conditions ∼1 ◦C warmer than present at ∼6200 (recalibrated 14C) and 4700 yr BP, with a suggested increase in salinity range (δ18O) associated with amplified seasonal flood events, suggestive of La Niña (Gagan et al., 1998; Roche et al., 2014).
Suvorov and Kitov, 2018 (Eastern Sayan, Siberia) The authors examined the variability of activity of modern glaciation and variation of natural conditions of the periglacial zone on climate and on dendrochronological data. Results of larch and Siberian stone pine growth data were revealed at the higher border of forest communities. … It is believed that the temperature could be 3.5 °C warmer at the Holocene optimum than at the present time (Vaganov and Shiyatov 2005). … Since 2000, there has been growth of trees instability associated with a decrease in average monthly summer temperatures. … Since the beginning of 2000, decrease in summer temperatures was marked.
Lozhkin et al., 2018 (East Siberia) The postglacial occurrence of relatively warm/dry and warm/wet intervals is consistent with results of a regional climate‐model simulation that indicates warmer than present temperatures and decreased effective moisture at 11 000 cal. a BP and persistence of warm conditions but with greater moisture and longer growing season at 6000 cal. a BP.
Xu et al., 2018 (Northern South China Sea) This study provides evidence that thermal coral bleaching events have occurred in the warmer mid-Holocene (where maximum monthly summer SST was 2 °C higher than at present) in Hainan island. … [C]oral bleaching events under high SST conditions have already occurred in the mid-Holocene and are by no means a new ecological phenomenon of current global warming.
Kullman, 2018 (Scandes, Northern Sweden) The present paper reports results from an extensive project aiming at improved understanding of postglacial subalpine/alpine vegetation, treeline, glacier and climate history in the Scandes of northern Sweden. The main methodology is analyses of mega fossil tree remnants, i.e. trunks, roots and cones, recently exposed at the fringe of receding glaciers and snow/ice patches. This approach has a spatial resolution and accuracy, which exceeds any other option for tree cover reconstruction in high-altitude mountain landscapes. … All recovered tree specimens originate from exceptionally high elevations, about 600-700 m atop of modern treeline positions. … Conservatively drawing on the latter figure and a summer temperature lapse rate of 0.6 °C per 100 m elevation (Laaksonen 1976), could a priori mean that, summer temperatures were at least 4.2 °C warmer than present around 9500 year before present. However, glacio-isostatic land uplift by at least 100 m since that time (Möller 1987; Påsse & Anderson 2005) implies that this figure has to be reduced to 3.6 °C higher than present-day levels, i.e. first decades of the 21st century. Evidently, this was the warmth peak of the Holocene, hitherto. This inference concurs with paleoclimatic reconstructions from Europe and Greenland (Korhola et al. 2002; Bigler et al. 2003; Paus 2013; Luoto et al. 2014; Väliranta et al. 2015).
Borisova, 2018 (central East European Plain) Paleobotanical assemblages from peat, lake, and archaeological deposits reveal that during the Middle Holocene (MH; ca. 9.0 to 4.7 kyr BP), the central East European Plain was occupied by highly productive and diverse mixed-oak forests, along with mire, meadow, and riverine communities. Climatic reconstructions based on modern analogues of fossil pollen and plant macrofossil assemblages indicate that throughout the MH [Middle Holocene] mean annual precipitation was at near present levels (~600 mm) and July temperatures were similar to those of today (~17°C). However, differences in the Fossil Floras (FFs) suggest changes in winter conditions though the MH [Middle Holocene, 9.0 to 4.7 kyr BP], with January temperatures higher than the present-day value of -10°C by 2°C in the Early Atlantic, 6°C in the Middle Atlantic, and 3°C in the Late Atlantic-Early Subboreal. The annual frost-free period was 15 days longer than today in the Early Atlantic, about one month longer in the Late Atlantic, and became close to present by the beginning of the Subboreal. The combination of warm winters with diverse and productive vegetation communities provided an environment that was more hospitable than that of today for Late Mesolithic and Neolithic societies.
McFarlin et al., 2018 (Greenland) Early Holocene peak warmth has been quantified at only a few sites, and terrestrial sedimentary records of prior interglacials are exceptionally rare due to glacial erosion during the last glacial period. Here, we discuss findings from a lacustrine archive that records both the Holocene and the Last Interglacial (LIG) from Greenland, allowing for direct comparison between two interglacials. Sedimentary chironomid assemblages indicate peak July temperatures [Greenland] 4.0 to 7.0 °C warmer than modern during the Early Holocene maximum [10,000 to 8,000 years ago] in summer insolation. Chaoborus and chironomids in LIG sediments indicate July temperatures at least 5.5 to 8.5 °C warmer than modern.
Bartels et al., 2018 (North Atlantic Region) During summer, AW [Atlantic Water] rises up to waterdepths as shallow as ~55 m. … Summer surface temperatures [1955-2012] range between up to 3°C at the northern mouth and <-1.5 °C at the southern mouth of the Hinlopen Strait, while winter surface temperatures vary between 0.5 and <~1.5°C (averaged, 1955–2012; Locarnini et al. 2013). … Increased summer insolation probably amplified the surface melting of the glaciers resulting in enhanced meltwater production and in a very high accumulation of finegrained sediments within the fjord […]. In addition, during the mild early Holocene conditions, summer sea-surface temperatures probably reaching 8–10°C [~5 – 9.5°C warmer than 1955-2012] (indicated by M. edulis findings as discussed in Hansen et al. 2011) may have contributed to reducing the number of glaciers that entered the fjord directly as tidewater glaciers and thus causing a diminished IRD input. These comparably warm surface temperatures most likely resulted in a reduced sea ice cover during summer, which is also reflected in the sea-ice biomarker data exhibiting lowest IP25 values during the early Holocene. … [G]lacier advances are most likely caused by atmospheric cooling as indicated, e.g. by d18O values from the Greenland NGRIP ice-core (Rasmussen et al. 2014a), by data from peats and permafrost soils on Spitsbergen (e.g. Humlum et al. 2003; Humlum 2005; Jaworski 2016), and by evidence that solar activity reduced around 2.7 ka, contributing to a cooling in both hemispheres (van Geel et al. 1999, 2000). … In lake sediments from northwestern Spitsbergen a temperature drop of ~6°C is recorded between c. 7.8 and c. 7 ka [-0.8°C per century], which has been connected to a stronger influence of Arctic Water and expanding sea ice (van der Bilt et al. 2018).
Lack Of Anthropogenic/CO2 Signal In Sea Level Rise
Khan, 2018 [T]hermal expansion only explains part (about 0.4 mm/yr) of the 1.8 mm/yr observed sea level rise of the past few decades. However, observation claim of 1.8 mm/yr sea level rise is also limited in scope and accuracy. … Claim and prediction of 3 mm/yr rise of sea-level due to global warming and polar ice-melt is definitely a conjecture. … Prediction of 4–6.6 ft sea level rise in the next 91 years between 2009 and 2100 is highly erroneous. … Hence, both regional and local sea-level rise and fall in meter-scale is related to the geologic events only and not related to global warming and/or polar ice melt. … In conclusion, global warming, both polar and terrestrial ice melts, and climate change might be a reality but all these phenomena are not related to sea level rise and fall.
Luijendijk et al., 2018 The application of an automated shoreline detection method to the sandy shorelines thus identified resulted in a global dataset of shoreline change rates for the 33 year period 1984–2016. Analysis of the satellite derived shoreline data indicates that 24% of the world’s sandy beaches are eroding at rates exceeding 0.5 m/yr, while 28% are accreting and 48% are stable. …. Erosion rates exceed 5 m/yr along 4% of the sandy shoreline and are greater than 10 m/yr for 2% of the global sandy shoreline. On the other hand, about 8% of the world’s sandy beaches experience significant accretion (>3 m/yr), while 6% (3%) are accreting more than 5 m/yr (10 m/yr). … Taking a continental perspective, Australia and Africa are the only continents for which net erosion (−0.20 m/yr and −0.07 m/yr respectively) is found, with all other continents showing net accretion.
Parker, 2018 Conclusion: The tide gauges of China are too short, or incomplete, to permit a proper assessment of the long-term trend, more than for the slope, certainly for the acceleration. … There is no clear evidence the sea levels of China are rising at an accelerating rate because of thermal expansion and mass addition, as the data available is either insufficient or conflicting. Conclusions about the sea levels of China may only be drafted from all the local relative rates of rise, and the global relative rates of rise and accelerations of different data sets. The slopes for the tide gauges of China and the slopes and accelerations for the worldwide tide gauges suggest that the coastal mean relative sea level in the China Seas very likely rises from −1 to 3 mm/year in the past half century and it may likely rise of 0–0.259 m in the twenty-first century.
Tomasicchio et al., 2018 The estimation of long-term sea level variability is of primary importance for a climate change assessment. Despite the value of the subject [sea level changes], no scientific consensus has yet been reached on the existing acceleration in observed values. … The Intergovernmental Panel on Climate Change (IPCC), an international organisation responsible for assessing the scientific basis of climate change, its impacts and future risks, warned that at current trends, the projected increments in mean sea level (MSL) for the year 2100, relative to the 1986–2005 period [IPCC] are 400, 470, 480 and 630 mm, for the Representative Concentration Pathways scenarios indicated as RCP2.6, RCP4.5, RCP6.0 and RCP8.5, respectively. However, from the tide gauge records, the acceleration required to reach these large projected MSL [mean sea level] rises over the course of the twenty-first century is not evident. Even though the measurement of this acceleration is a topic with a long standing history (Douglas 1991; Church and White 2006; Jevrejeva et al. 2008), the most recent debate was initiated by a series of publications (Houston and Dean 2011a, b, c, d, e) that raised concerns about the general validity of the sea level projections; the authors did not find any acceleration in the sea level in USA tide gauge records during the twentieth century. Instead, for each time period they considered, the records showed small decelerations that are consistent with a number of earlier studies of worldwide gauge records (Woodworth 1990; Douglas 1992; Woodworth et al. 2009). By using a different approach in data analysis, other researchers (Rahmstorf and Vermeer 2011a, b; Donoghue and Parkinson 2011a, b) found the arguments of Houston and Dean (2011a, b, c, d, e) not convincing and showed that accelerations are present.
Frederiske et al.,2018 For the first time, it is shown that for most basins the reconstructed sea level trend and acceleration can be explained by the sum of contributors, as well as a large part of the decadal variability. The global-mean sea level reconstruction shows a trend of 1.5 ± 0.2 mm yr−1 over 1958–2014 (1σ), compared to 1.3 ± 0.1 mm yr−1for the sum of contributors.
[Global sea levels rose 3.1 inches (1.4 mm/yr) between 1958-2014, with 0.59 of an inch meltwater contribution from the Greenland and Antarctic ice sheets combined.]
Kench et al., 2018 We specifically examine spatial differences in island behaviour, of all 101 islands in Tuvalu, over the past four decades (1971–2014), a period in which local sea level has risen at twice the global average (Supplementary Note 2). Surprisingly, we show that all islands have changed and that the dominant mode of change has been island expansion, which has increased the land area of the nation. … Using remotely sensed data, change is analysed over the past four decades, a period when local sea level has risen at twice the global average [<2 mm/yr-1] (~3.90 ± 0.4 mm.yr−1). Results highlight a net increase in land area in Tuvalu of 73.5 ha (2.9%), despite sea-level rise, and land area increase in eight of nine atolls.
Ahmed et al., 2018 This paper draws upon the application of GIS and remote sensing techniques to investigate the dynamic nature and management aspects of land in the coastal areas of Bangladesh. … This research reveals that the rate of accretion [coastal land growth] in the study area is slightly higher than the rate of erosion. Overall land dynamics indicate a net gain of 237 km2 (7.9 km2annual average) of land in the area for the whole period from 1985 to 2015.
Parker et al., 2018 The anomalous pattern of relative sea levels for the Samoan Islands that followed the 2009 earthquake and tsunami is explained by coupling tide-gauge time series of relative sea levels and GPS time series of absolute geocentric positions of inland fixed domes. The subsidence of the land is responsible for the relative sea level acceleration that followed the earthquake. The pattern of subsidence is characterized by small departures from a linear pattern immediately before the earthquake, an abrupt change at the earthquake, and then a parabolically reducing extra subsidence. The absolute geocentric sea levels obtained clearing the relative sea level signal of the subsidence signal are stable. There is a need to couple GPS monitoring of tide gauge position with tide gauge measurements of relative sea levels without any linearity assumption to produce reliable, accurate, assessments of the pattern of sea level rise to inform policy makers.
Sea Levels Multiple Meters Higher Than Present 4,000-7,000 Years Ago
Escobar-Torrez et al., 2018 (W Borneo, South China Sea) The predictions for a range of earth models show RSL [relative sea level] rising steeply up to 7000 yr BP, slowing thereafter, and peaking at 5000 yr BP with an elevation of 0.80–3.10 m above present.
Clemmensen et al., 2018 (N Denmark) The raised spit deposits at Skagen Odde, northern Denmark, offer a unique possibility to study spit evolution over the past 7600 years. The deposits contain well-preserved beach facies including the transition from wave-formed foreshore to aeolian-influenced backshore sediments. After correction foroffset and isostatic spatial gradient, we have been able to use this boundary as a proxy for palaeo-sea level. Measurements at 57 sample sites covering ~17 km along the northwestern coast of the spit indicate that this boundary first rises towards the northeast, then reaches a maximum relative sea level at about 12.5 m above present mean sea level [apmsl] before gradually decreasing toward the most recent part of the spit. By pairing all boundary elevation measurements with an OSL age, the variation in elevation with age has been determined directly. The resulting curve reflects variation in relative sea level with time; we conclude that relative sea level initially rose between c. 7600 and c. 6250 years ago, reached a first peak value around 12.5 m apmsl [above present mean sea level] and a second peak value around 11 m apmsl [above present mean sea level] c. 4600 years ago before it dropped to reach 2 m apmsl [above present mean sea level] c. 2000 years ago.
Cooper et al., 2018 With sea level stabilization a few metres above the present around 5.5 ka cal yr BP (Hein et al., 2016), the longshore drift system was reestablished and sediment accumulation in the littoral zone recommenced.
Wündsch et al., 2018 Holocene sea level reconstructions suggest a reduction of the speed of the sea level rise during this time [~7900–6400 cal BP]. The sea level likely reached and exceeded the height of the PSL [present sea level] by as much as 3 m (Compton, 2001).
Song et al., 2018 A sea-level curve for the west coast of South Korea was reconstructed. Sea level rose rapidly at a rate of ~1.4 cm yr–1 from 9.8–8.4 cal kyr B.P. [1.4 meters per century] and rose gradually until the mid-Holocene, after which it fell gradually to the present. There is a sea-level highstand of 1–2 m [above present] from 7–4 cal kyr B.P., likely due to hydro-isostatic effects. The rapid sea-level rise during the early Holocene is clearly a manifestation of polar ice sheet decay. The results were supported by the GIA model. The Holocene RSL change on the west coast of South Korea was closely linked to global temperature and ice sheet decay, especially during the early Holocene.
A Model-Defying Cryosphere, Polar Ice
Rösel et al., 2018 We present a continuous time series of in situ measurements from the N‐ICE2015 expedition from January to June 2015 in the Arctic Basin north of Svalbard, comprising snow buoy and ice mass balance buoy data and local and regional data gained from electromagnetic induction (EM) surveys and snow probe measurements from four distinct drifts. The observed mean snow depth of 0.53 m for April to early June  is 73% above the average value of 0.30 m from historical [1955, 1970s] and recent observations in this region, covering the years 1955–2017. The modal total ice and snow thicknesses, of 1.6 and 1.7 m  measured with ground‐based EM and airborne EM measurements in April, May, and June 2015, respectively, lie below the [1970s] values ranging from 1.8 to 2.7 m, reported in historical observations from the same region and time of year [but well above the sea-ice thickness values of 0.94 m for 1955].
Shakun et al., 2018 Here we show that land-based sectors of the EAIS [East Antarctic Ice Sheet] that drain into the Ross Sea have been stable throughout the past eight million years. … These findings indicate that atmospheric warming during the past eight million years was insufficient to cause widespread or long-lasting meltback of the EAIS [East Antarctic Ice Sheet] margin onto land. We suggest that variations in Antarctic ice volume in response to the range of global temperatures experienced over this period—up to 2–3 degrees Celsius above preindustrial temperatures, corresponding to future scenarios involving carbon dioxide concentrations of between 400 and 500 parts per million—were instead driven mostly by the retreat of marine ice margins, in agreement with the latest models.
Arndt et al., 2018 Pine Island Glacier is the largest current Antarctic contributor to sea level rise. Its ice loss has substantially increased over the last 25 years through thinning, acceleration and grounding line retreat. However, the calving line positions of the stabilizing ice shelf did not show any trend within the observational record (last 70 years) until calving in 2015 led to unprecedented retreat and changed alignment of the calving front. … Despite the thinning and flow acceleration of PIG [Pine Island Glacier], and sustained, rapid thinning of the ice shelf over at least the past 25 years the position of the ice front had not shown any clear trend over 68 years of observations prior to 2015 (Bindschadler, 2002;MacGregor et al., 2012;Rignot, 2002).
Medley et al., 2018 East Antarctic Ice Sheet (EAIS) mass balance is largely driven by snowfall. Recently, increased snowfall in Queen Maud Land led to years of EAIS mass gain. It is difficult to determine whether these years of enhanced snowfall are anomalous or part of a longer-term trend, reducing our ability to assess the mitigating impact of snowfall on sea-level rise. We determine that the recent snowfall increases in western Queen Maud Land (QML) are part of a long-term trend (+5.2±3.7% decade-1) and are unprecedented over the past two millennia. Warming between 1998 and 2016 is significant and rapid (+1.1±0.7 °C decade-1). Using these observations, we determine that the current accumulation and temperature increases in QML from an ensemble of global climate simulations are too low, which suggests that projections of the QML [Queen Maud Land] contribution to sea-level rise are potentially overestimated with a reduced mitigating impact of enhanced snowfall in a warming world.
Treat and Jones, 2018 Rates of permafrost aggradation in peatlands generally increased after 3000 BP and were greatest between 750 and 0 BP [today], corresponding with neoglacial cooling and the Little Ice Age (LIA), respectively.
Nature Geoscience, 2018 The East Antarctic ice sheet may be gaining mass in the current, warming climate. The palaeoclimate record shows, however, that it has retreated during previous episodes of prolonged warmth. … In terms of immediate sea-level rise, it is reassuring that it seems to require prolonged periods of lasting hundreds of thousands to millions of years to induce even partial retreat.
Rysgaard et al., 2018 The Greenland ice sheet (GIS) is losing mass at an increasing rate due to surface melt and flow acceleration in outlet glaciers. … Recently it was suggested that there may be a hidden heat source beneath GIS caused by a higher than expected geothermal heat flux (GHF) from the Earth’s interior. Here we present the first direct measurements of GHF from beneath a deep fjord basin in Northeast Greenland. Temperature and salinity time series (2005–2015) in the deep stagnant basin water are used to quantify a GHF of 93 ± 21 mW m−2 which confirm previous indirect estimated values below GIS. A compilation of heat flux recordings from Greenland show the existence of geothermal heat sources beneath GIS and could explain high glacial ice speed areas such as the Northeast Greenland ice stream. … Geothermal springs with source water temperatures above 0 °C have been found all over Greenland, especially around Disko Island in West Greenland, where several thousands of such springs have been identified. … However, the hottest springs, with source water temperatures of 55-62 °C are found in East Greenland at a number of locations north and south of Scoresbysund. … Overall, there has been a gradual warming of the stagnant deep basin bottom water below 240 m depth of 0.017 °C yr−1 from 2005 to 2015. … [T]he gradual temperature increase during 2006–2015 and the spatial distribution of Δθ strongly indicate that bottom water temperatures increase due to a large GHF [geothermal heat flux] in the “Dybet” section. Therefore, we assume that vertical turbulent mixing and GHF [geothermal heat flux] are the primary processes behind the observed salinity and temperature change. … High glacier surface speeds and negative mass balance are also observed near other hot vents in West Greenland such as the Jakobshavn Isbræ (69°N) near Disko Island; [T]he Narssaq bræ, Valhaltinde glacier, Nordbo glacier and Qassimiut ice lobe in South Greenland all show negative ice mass balances near the hot vent in Uunartoq (60°N); [I]n East Greenland the Helheim glacier, Isertoq and Mittivakkat glaciers located near Ikasagitavaq (66°N) are losing mass, and high ice speed is also observed at the Kangerdlugssuaq glacier where a GHF [geothermal heat flux] of 70–80 mW m−2 has been recorded (68°N). In addition, a GHF value of 135 mW m−2 has been reported at NGRIP [North Greenland].
Oppedal et al., 2018 This advance was documented by historical evidence (Hayward, 1983), showing that many glaciers advanced in the twentieth century. Cirque and valley glaciers were at its most advanced position in the 1930s, while larger valley and tidewater glaciers reached their maximum glacier extent in the 1970s. Such a glacier advance is also documented for the Hamberg glacier by Van Der Bilt et al. (2017). Furthermore, during the recession phase after the twentieth century advance, many cirque glaciers deposited annual moraines (Gordon and Timmis, 1992), such as the ones observed in the innermost moraine cluster. Thus, Diamond glacier followed a similar pattern to that observed for small glaciers (0.1–4.0 km2) on South Georgia during the late Holocene, with a Little Ice Age advance, a period of recession, a twentieth century advance and a recent recession (Gordon and Timmis, 1992).
Allan et al., 2018 Our record shows variations with a mean 200 years periodicity until ~2 ka BP, which supports the hypothesis of climate variations driven by solar variability. After 1.5 ka BP, our data show a variability characterized by a 60–70 year periodicity, which suggests linkages with the Atlantic Multidecadal Oscillation and southwestward migration of the atmospheric polar front. The most recent part of the record, from ~1900 CE to 2007 CE, is characterized by assemblages reflecting warmer surface conditions and reduced sea ice cover.
Kelley et al., 2018 In this study, we reconstruct the timing and pattern of middle- and late-Holocene GrIS [Greenland Ice Sheet] margin fluctuations at two locations, ~190 km apart, in central West Greenland using radiocarbon-dated sediment cores from proglacial-threshold lakes. Our results demonstrate that deglaciation occurs at both sites during the early Holocene, with the ice sheet remaining in a smaller-than-present ice margin configuration until ~500 years ago when it readvanced into lake catchments at both sites. … Historical and remote-sensing records indicate that Nordenskiöld Gletscher has been stable or advancing since AD 1950 (Weidick, 1968, 1994). This evidence, in addition to the lack of a moraine or trimline marking the culmination of the late-Holocene advance fronting the ice margin, as occurs across much of the region, infers that the system is at or is still advancing to its late Holocene maximum extent. We note the difference between the ice margin locations on the laterals versus the terminus relative to the late-Holocene maximum position and attribute this to deepening of the glacial trough as described by Kaplan et al. (2009). In fact, observations at the terminus of Nordenskiöld Gletscher in 2013 documented that the terminus is currently advancing onto living tundra.
Méheust et al., 2018 In this study, the last glacial–deglacial–Holocene variability in SST [sea surface temperature] and sea-ice cover are reconstructed using alkenone-based SST [sea surface temperature] and sea-ice IP25 and PIP25 proxies in sediment cores from the Bering Sea [Arctic Ocean] and the subarctic Pacific. At all sites and during warm as well as cold climatic intervals SST values are well above 0 °C, suggesting ice-free summer conditions throughout. … The early Holocene is marked by distinctly increased TOC contents, reaching maximum values (>1 wt%) between ~400 and ~170 cm (~11.5–10 ka ~11,500 to 10,000 years ago]). Likewise, continuously increasing SST [sea surface temperature], reaching maximum values of ~ 9°C at ~ 180 cm (~ 10 ka [10,000 years ago]), strongly coincides with the absence of IP25 [proxy for sea ice] in the sediment. … [For the] lower half of the studied section of Core SO202-27-6 [North eastern Pacific], the Holocene is characterized by maximum SST [sea surface temperature] values of 12°C. Relatively low TOC and phytoplankton markers prevailing during this period, coeval with the absence of IP25 [sea ice]. … [For the] North western Pacific (Core SO202 07 6), the Holocene is marked by the absence of IP25 [sea ice], coinciding with low values of TOC, dinosterol and long chain n-alkanes (avg. ~0.5 wt%, ~ 4 µg/g TOC and 78 µg/g TOC, respectively). SST [sea surface temperature] values increase to about 10°C during the early Holocene. … At all sites and during warm as well as cold climatic intervals SST values are well above 0 °C (i.e., ranging between about 5 and 12°C), suggesting that the SST data represent more the summer situation with ice-free conditions.
In the Bering Sea, the transition between the YD [Younger Dryas]-like cold event and the Early Holocene is marked by the rapid disappearance of IP25 [sea ice] around 11.5 ka [11,500 years ago] in both cores from the Bering Sea. The absence of IP25 [sea ice proxy] and minimum PIP25 [sea ice proxy] index values is also registered in the subarctic Pacific during this period. These observations demonstrate that year-round open-water conditions prevailed in these areas during the Early Holocene. … A prominent decrease of IP25 [sea ice proxy] and minimum values of PIP25 index, reflecting ice-free conditions in the subarctic Pacific and the Bering Sea during the Holocene Thermal Maximum, is in line with the SST [sea surface temperature] warming. This is likely due to the maximum orbitally forced summer insolation, enhancing the melting of ice sheets and thus a sea-level rise.
Przybylak et al., 2018 Analysis reveals that the expedition year 1944/1945 in Nordaustlandet was, in the majority of months, the warmest of all analysed periods, that is, both historical and contemporary periods. The study period was markedly warmer than 1981–2010 (mean annual −6.5 vs. −8.4°C) but colder than the periods 2011–2016 (−5.7°C) and 2014–2017 (−5.8°C). … Generally, no change is observed in frequency of occurrence of cold days between the ETCWP [early twentieth century warm period] and CWPs [contemporary warm periods]. A slightly smaller number of cold summer days occurred in the ETCWP than occur at present. … The majority of mean monthly air temperatures in the ETCWP [early twentieth century warm period] is within two SDs of the modern 1981–2010 mean. This means that values of air temperature in the study period [1944/1945] lie within the range of recent temperature variability. Similar results were obtained for older historical periods, for example, for the Canadian Arctic, the entire Svalbard archipelago and surrounding seas, Novaya Zemlya as well as for the entire Arctic.
Sigl et al., 2018 No role for industrial black carbon in forcing 19th century glacier retreat in the Alps … Starting around 1860 AD, many glaciers in the European Alps began to retreat from their maximum mid-19th century terminus positions, thereby visualizing the end of the Little Ice Age in Europe. Radiative forcing by increasing deposition of industrial black carbon to snow has been suggested as the main driver of the abrupt glacier retreats in the Alps. … Our study reveals that in 1875 AD, the time when European rBC [industrial black carbon] emission rates started to significantly increase, the majority of Alpine glaciers had already experienced more than 80% of their total 19th century length reduction. Industrial BC emissions can, therefore, not been considered as the primary forcing for the rapid deglaciation at the end of the Little Ice Age in the Alps.
Ronkainen et al., 2018 In our study, we quantify the interannual variability of sea ice thickness in the Bay of Bothnia during the years 2003-2016.
Stabeno et al., 2018 From 2007 to 2013, the southeastern Bering Sea was dominated by extensive sea ice and below-average ocean temperatures. In 2014 there was a shift to reduced sea ice on the southern shelf and above-average ocean temperatures. These conditions continued in 2015 and 2016. … Historically, the dominant parameters controlling sea-ice extent are winds and air temperature, with the persistence of frigid, northerly winds in winter and spring resulting in extensive ice. After mid-March 2014 and 2016 there were no cold northerly or northeasterly winds. Cold northerly winds persisted into mid-April in 2015, but did not result in extensive sea ice south of 58°N. The apparent mechanism that helped limit ice on the southeastern shelf was the strong advection of warm water from the Gulf of Alaska through Unimak Pass. This pattern has been uncommon, occurring in only one other year (2003) in a 37-year record of estimated transport through Unimak Pass. During years with no sea ice on the southern shelf (e.g. 2001–2005, 2014–2016), the depth-averaged temperature there was correlated to the previous summers ocean temperature. … This latest string of three warm years apparently ended this year (2017). In March, sea ice had covered M4, and the ice edge was near or at M2 on 13 March 2017, but by June 2017 the depth-averaged temperatures at M2 were average, indicating that ocean temperature near M2 in 2017 (like the 2006 transition between the previous warm and cold stanzas) will likely be average. With this end of a warm stanza, questions arise. Will the Bering Sea continue in a pattern of warm/cold stanzas?
Mass Extinction Events Caused By Global Cooling, Glaciation, Sea Level Fall
Isozaki and Servais, 2018 Besides the similarity in extinction patterns with the preferential elimination of particular clades, we can recognize a major resemblance but of non-biotic nature between the [Ordovician] Hirnantian and [Permian] Capitanian [mass extinction] events, that is the significant cooling coupled with global sea-level drop. … A sea-level drop of nearly 100 m can be achieved solely by transferring vast seawater onto land in the form of ice. It is noteworthy that sea level was much higher in the Late Ordovician (ca. 60 m above the present-day level) than in the Middle Permian (ca. 80 m below the present-day level), even after the sea-level drop in the same magnitude. … The lines of evidence for cooling and relevant sealevel drop during the Hirnantian [Ordovician] are listed as follows: (1) sequence stratigraphy (Haq & Schutter 2008; Fig. 2); (2) regional occurrence of glacial sediments, including tillite/dropstone, mostly in Gondwana (e.g. Brenchley et al. 1994; Ghienne 2003); and (3) isotope signature in seawater (Trotter et al. 2008). On the basis of these, there was a solid consensus among researchers for the link between the global cooling and the first Hirnantian extinction; however, recent studies indicate that the cooling may have started not necessarily at the beginning of the Hirnantian but much earlier, probably already in the Middle Ordovician (Vandenbroucke et al. 2010; Finnegan et al. 2011; Nardin et al. 2011; Rasmussen et al. 2016). Nevertheless, sea level dropped nearly 100 m in the Hirnantian (e.g. Haq & Schutter 2008). Traditionally, the existence of a continental block (Gondwana) over the South Pole was required for the development of ice sheets. … The evidence for the late Capitanian global sealevel drop (for up to 100 m) is robust. … The sharp erosion of reef limestone in low-latitude mid-ocean implies a large eustatic sea-level drop, in other words, the appearance of a global cooling. … The biotic responses in the Hirnantian and Capitanian appear compliant with all these lines of evidence for cooling, in particular, the latitudinal contraction of faunal distributions towards tropics together with the preferential elimination of preexisting tropical fauna. Regardless of the second Hirnantian episode, the first decline in biodiversity in both cases occurred during global cooling. In general, a relative drop in seawater temperature, particularly in shallow seas, is critical for the metabolism of almost all contemporary marine organisms. The updated lines of evidence therefore confirmed the classic notion of a putative link between the global cooling and extinction (e.g. Stanley 1988) for both cases [the Ordovician and Permian extinction events].
Kani et al., 2018 The end-Middle Permian extinction was in fact a prolonged but gradual decrease in diversity from the Wordian to the end of the Capitanian (Clapham et al., 2009). The main phase of the extinction appears to have occurred almost simultaneously during the Capitanian minimum of Sr isotope records. … [T]he sea level during the Capitanian contradictorily recorded the lowest stand of the Phanerozoic (Haq and Schutter, 2008), suggesting a global cooling instead [caused the Permian extinction]. Ice coverage and/or the predominance of arid climates under cooling during the Permian likely accelerated the decrease in the seawater Sr ratio. … In general, the termination of shallow marine carbonates may occur with a decrease in the seawater temperature. Two possible causes can be inferred for the late Capitanian temperature decrease, i.e., 1) the appearance of global cooling, and 2) the migration of depositional sites to higher latitudes with cooler climates. The Capitanian global cooling was proposed first on the basis of the unique carbon isotope record in low-latitude paleo-atoll carbonates (12°S) (Isozaki et al., 2007), a signature that was reproduced later in other parts of the world, e.g., in Croatia and in South China (Isozaki et al., 2011; Chen and Benton, 2012). In addition, in a global summary of sequence stratigraphy (Haq and Schutter, 2008), the findings of coeval glacial deposits in eastern Australia and in Mongolia (Fielding et al., 2008; Fujimoto et al., 2012), the selective extinction of tropical fauna (Isozaki and Aljinovic, 2009), the migration of mid-latitude fauna to low latitudes (Shen and Shi, 2002), and the Milankovitch tuning (Fang et al., 2017), all support the onset of cooling in the Capitanian. … [T]he Capitanian under a cooling trend […] [coincided with the] lowest sea level of the Phanerozoic and […] the preferential elimination of tropical fauna. … [T]he appearance of extensive ice coverage over continental blocks might have occurred, and the weathering/erosion of continental crust could have been suppressed to drive a lower riverine flux with high 87Sr/86Sr ratios. Alternatively, an arid weathering regime might have developed extensively under the cool climate, particularly on the vast supercontinent Pangea, which also contributed to suppressing the riverine fluxes (Korte et al., 2006).