600 Non Warming Graphs (1)

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Tamo and Gajewski, 2019

Reconstructed July temperatures ranged from 4.5 to 8.0°C and showed a cooling trend of about 1.5°C from 1080–1915 CE and with lowest temperatures (4.5°C) reconstructed between 1800 and 1915 CE. Temperatures rose over the last 100 years to between 5 and 6°C, which is comparable to MCA values (Figure 4). … Other reconstructions with an average temporal resolution of less than 100 years between data points (SL06 and MB01, Peros and Gajewski 2009) and one slightly lower resolution record (JR01, Zabenskie and Gajewski 2007) showed some between-site congruence with SW08 (Figure 6). Two of the sites (SL06 and MB01) recorded warmer temperatures during most of the first millennium, and the longer records showed a centennial-scale cooling trend in the Common Era. All four sites reconstructed a relative cooling between 1800 and 1930 CE when temperatures decreased by 0.5–1.5°C from the mean of the last 1,000 years for each record. Although each site experienced a cold period of similar amplitude, the duration varied between sites. SW08 and SL06 recorded a longer sustained cold period from 1800–1930 CE and 1775–1950 CE, respectively. At SL06, this period was an intensification of colder conditions that began at ~1100 CE, whereas at SW08 there was more variability prior to 1800 CE.”

Tonno et al., 2019

“In North Europe, changes in early Holocene climate were rather intense, starting with low temperatures at the beginning of the period, followed by gradual warming, interrupted periodically by short cooling periods (Antonsson and Seppa¨ 2007). During the Holocene Thermal Maximum (HTM), the period from 8.0 to 4.0 cal ka BP, average temperatures in Northern Europe were approximately 2.5–3.5 C higher than today (Antonsson and Seppa¨ 2007; Heikkila¨ and Seppa¨ 2010; Ilvonen et al. 2016).”

Lacka et al., 2019

Sea ice-free conditions remained during most of the mid-Holocene as a result of the influence of AW [Atlantic Water] (Łacka et al., 2015b). These conditions coincided with the highest Holocene primary productivity observed on the northern continental slope of the Barents Sea (Wollenburg et al., 2004). The northern Barents Sea experiences seasonal sea ice cover that forms during fall/winter (Loeng, 1991). Sea ice breakup occurs during summer, leading to open-water conditions in August and September (Belt et al., 2015). … The SSTs at the study site during the B-A varied between 2°C and 4°C, which is comparable to modern SST values in Storfjordrenna [~3°C]. … Between 9200 cal yr BP and 3400 cal yr BP, SSTs in Storfjordrenna remained highly variable (from 3°C to almost 13°C). At approximately 6400 cal yr BP, the SST in Storfjordrenna reached a peak of almost 13°C (Fig. 3B).”

van der Bilt et al., 2019

“Alkenone data show that Svalbard experienced summer temperatures both warmer and colder than today during the Early Holocene. Warmth was greatest around 10 ka BP, when temperatures were up to ~7 °C higher than present in response to high radiative forcing and intensified ocean heat advection. In agreement with a growing body of recent work (e.g. Lecavalier et al., 2017; McFarlin et al., 2018), these findings indicate an earlier and  warmer Holocene Optimum in the High Arctic then previously suggested. Supporting these findings, Mangerud and Svendsen (2018) derive a similar amplitude for peak Holocene warmth, based on the presence of Zirfaea crispata, a thermophilous mollusc that is not present in Svalbard waters today. … As seen in Figure 2e, sub-surface temperatures display a prominent peak around 10 ka BP that is unmatched in the remainder of the Holocene. Werner et al. (2015) infer a similar pattern of temperature change in the adjacent eastern Fram Strait. In addition, an IP25 reconstruction from the same site suggests that the seasonal sea ice margin had retreated north of Svalbard at this time. … Placed in a regional context, our findings support a number of recent studies that suggest an earlier, warmer and more distinct Arctic Holocene optimum (Lecavalier et al., 2017;  McFarlin et al., 2018). Collectively, this body of work stresses the need for data-model comparisons as simulations neither reproduce this reconstructed pattern nor its magnitude (Figure 2c; Zhang et al., 2018).”

Collins et al., 2019

“Over the past 2300 yrs, SST values range between 14.3°C and 12.2°C (Fig. 4a), and hence most of the record is warmer than today. The earlier half of the record is relatively warm and stable and displays a gradual warming from 13.2°C at 2300 cal yrs BP to 14°C at 1200 cal yrs BP. The largest feature of the record is the cooling transition from 14°C to 12.5°C between 1100 and 600 cal yrs BP. This is followed by warming to 13.5°C at 300 cal yrs BP and then cooling to 12.5°C at present day. Multi-centennial variability is more clearly highlighted in the filtered record and is most pronounced over the last 1200 years. The record exhibits relatively warm conditions during the periods 1200 – 950 cal yrs BP and 500 – 200 cal yrs BP and relatively cool conditions during the periods 950 – 500 cal yrs BP and 200 – present. … Southern Ocean cooling is expected to have further enhanced sea ice cover in the Southern Ocean (Park and Latif, 2008; Zhang et al., 2017a). This is in accordance with two records displaying increased sea ice in the western Ross Sea at a similar timing (between 1250 and 650 cal yrs BP) to the cooling (Mezgec et al., 2017). Late Holocene sea-ice increases are also observed to the west of the Ross Sea (Denis et al., 2010), to the west of the West Antarctic Peninsula (Etourneau et al., 2013) and in the Eastern Ross Sea (Mayewski et al., 2013). Associated ice-albedo and ice-insulation feedbacks (Renssen et al., 2005; Varma et al., 2012) may have contributed to the rapidity of the cooling and sea-ice expansion. … Solar variability would be a potential driver of the changes in ENSO and SAM coupling. Increased (decreased) TSI has been shown to promote La-Niñalike (El-Niño-like) conditions by enhancement of the trade winds (Mann et al., 2005). Similarly, the SHW are sensitive to the 11yr solar cycle (Haigh et al., 2005) and solar variability on centennial timescales (Varma et al., 2011) and thus solar variability might be expected to exert an influence on the SAM. Therefore, it is plausible that solar variability may have controlled the phasing of ENSO and the SAM, and this remains an interesting avenue for further climate modeling research.”

Lüning et al.,2019

“Until recently, the Antarctic Peninsula and West Antarctica were among the most rapidly warming regions on Earth. Between the 1950s and 1990s temperatures on the Antarctic Peninsula increased by more than 0.3°C/decade (Stenni et al., 2017; Turner et al., 2016; Vaughan et al., 2003), with even higher warming rates reported for Byrd Station in West Antarctica (Bromwich et al., 2013; Bunde et al., 2014; Nicolas and Bromwich, 2014). Since the late 1990s, however, this warming has essentially stalled. Rapid cooling of nearly 0.5°C per decade occurred on the Antarctic Peninsula (Favier et al., 2017; Fernandoy et al., 2018; Turner et al., 2016). This already impacted the cryosphere in parts of the Antarctic Peninsula, including slow-down of glacier recession, surface mass gains of the peripheral glacier and a thinning of the active layer of permafrost in the northern Antarctic Peninsula islands (Engel et al., 2018; Oliva et al., 2017; Seehaus et al., 2018). At the same time, temperatures in West Antarctica over the past two decades appear to have plateaued or slightly cooled (Bromwich et al., 2013; Jones et al., 2016; Steig et al., 2009). However, temperature records in West Antarctica are few, often discontinuous and show opposing trends from location to location (Shuman and Stearns, 2001) which complicates modern trend analysis in this part of Antarctica. In contrast, East Antarctica has not experienced any significant temperature change since the 1950s (e.g. Yang et al., 2018) and some areas appear to have even cooled during the most recent decades (Clem et al., 2018; Favier et al., 2017; Jones et al., 2016; Marshall et al., 2014; Nicolas and Bromwich, 2014; O’Donnell et al., 2011; Ramesh and Soni, 2018). Cooling and an increase in snowfall in East Antarctica seems to have led to a gain in ice sheet mass and thickening of ice rises over the past 15 years (Goel et al., 2017; MartinEspañol et al., 2017; Philippe et al., 2016; Zwally et al., 2015). East Antarctic marine-terminating glaciers show no systematic change over the past 50 years (Lovell et al., 2017). Lastly, also the surface layers of the Southern Ocean south of 45°S has predominantly cooled over that past three decades (Armour et al., 2016; Fan et al., 2014; Kusahara et al., 2017; Latif et al., 2017), whilst the subpolar abyssal waters are warming (Sallée, 2018).”

Lohmann et al., 2019

Pitulko et al., 2019

“Our data show that from c. 10 600 BP, Zhokhov Island was situated on the margin of the shrinking Arctic coast (Anisimov et al. 2009); this is supported by the presence of a large quantity of driftwood that washed ashore at the Zhokhov site. The environmental situation was relatively favourable for human occupation: the climate was [5-6°C] warmer than today, and Zhokhov Island was covered by an Arctic tundra comprising sedge grass, shrubs and dwarf birch (Makeyev et al. 2003).”

Salvatteci et al., 2019

“[O]tolith δ18O data from Peruvian catfish (Galeichthys peruvianus) excavated from archeological sites in northern Peru suggest SST ~4 °C warmer than presentday SST (Andrus et al., 2002).”

Wang and Zhang, 2019

Lüning et al., 2019

The main MCA warming phase coincides with a higher SAM, more El Niño-dominated ENSO, more positive IPO and higher solar activity (Abram et al., 2014; Conroy et al., 2008; Steinhilber et al., 2012; Vance et al., 2015) (Fig. 5). Spectral analysis of the classical Mt Read tree rings series (site 5), yields characteristic cycle periods associated with the solar Gleissberg (80 years) and Suess-de Vries (210 years) cycles (Cook et al., 1995; Cook et al., 2000). … An alternation of well-defined multicentennial warm and cold phases has been reconstructed for Grotto of Oddities in SE Australia (site 3). Temperatures oscillated with an amplitude of more than 1°C during the past 1500 years (McGowan et al., 2018).”

Emslie and Meltzer, 2019 Colorado, USA

“Ultimately, however, the most significant changes in climate and biota in the UGB [Upper Gunnison Basin, Colorado] occurred in the Early to Middle Holocene, when incoming solar radiation peaked, summer temperature increased, and effective precipitation decreased. As a result, biotic communities changed: the upper tree line shifted upslope to perhaps 270 m higher than today [1.6°C higher temps with 0.6°C/100 m lapse rate] (Fall,1997b).”

Aguirre et al., 2019

A SST rise of ca. 1-2°C during the Hypsithermal (ca. 7.5-4.5 ka B.P.) in comparison with the modern average oceanic temperatures is independently supported by the palaeobiogeographical pattern of stenothermal gastropods and bivalves northwards displaced at present (“anomalous taxa”; Aguirre, 1993, Aguirre et al., 2011, 2017) together with the absence of the cold gastropod T. atra (Aguirre et al., 2013) and is sufficient to have displaced winds, shallow water masses and the Brazil Malvinas Confluence southwards along Patagonia. … The mid-Holocene and Last Interglacial were warmer than today due to a southward shifted BMC, stronger and poleward shifted southern westerlies winds, enhanced ACC and subantarctic shelf water, and intensified ocean fronts/upwelling levels.”

Kuzmina et al., 2019

Even during coldest time of the Pleistocene, the Last Glacial Maximum (LGM), summer temperatures were higher here than they are today (Alfimov, Berman, 2001, Alfimov et al., 2003). … The Pleistocene megafauna of the North Slope was dominated by mostly horses … There are depressions in the main Pleistocene unit filled by early Holocene sediments containing well-preserved leaves, logs and stumps of Populus balsamifera. Since the modern limit of this tree species is south of the North Slope, the presence of fossil poplar indicates warmer than present climate during the early Holocene. … The second warming (around 9–8 ka), which corresponds with Boreal Period of the BlyttSernander scheme, was probably the warmest interval of the Holocene in Beringia (Kaufman et al., 2004). Trees spread north to coastal areas in Siberia (Kaplina, Lozhkin, 1982; Kuzmina, Sher, 2006), spruce forest reached the central Brooks Range (Anderson, Brubaker, 1994), and beaver occupied formerly treeless landscapes in Alaska (Robinson et al., 2007). Climate on the North Slope was about 2 to 3°C warmer than today; and moisture was lower (Nelson, Carter, 1987).”

Girardin et al., 2019

For the most recent 11 years on record (2005–2016), Greenland temperature has exhibited a slightly decreasing trend consistent with northern North Atlantic-wide cooling during that period (figure S15) and a slowdown of the Atlantic Ocean overturning circulation (Thornalley et al 2018). The proportion of forest that was affected by extreme biomass burning also declined during this period (figures 1 and S7). … Two periods of high sub-continental biomass burning and p̂CHAR (i.e. 4950–4750 BP and 1250–1050 BP) are found during some of the periods of warmest Holocene temperatures in Greenland (respectively about +2.4 °C and +3.4 °C above the 1951–1980 baseline; figure 4(e); Kobashi et al 2017). Both periods coincide with positive temperature anomalies that have been inferred from chironomid assemblages in eastern boreal North American lakes (+2.1 °C and 2.2 °C above baseline (Bajolle et al 2018, figure S11).”

Curran et al., 2019

“[R]ecords for the Northgrippian from the East Greenland margin provide no evidence of increased calving of the Greenland Ice-Sheet (Jennings et al., 2002, 2011; Risebrobakken et al., 2011). This is likely due to the absence of sustained marine-terminating glaciers on the East Greenland margin during the warmer than present Northgrippian (Larsen et al., 2015). … The intervals of warmest BWT [bottom water temperatures] occurred between ca. 4-5 ka and between 2.2 ± 0.1 ka and 2.4 ± 0.2 ka. … Mg/Ca measurements from gravity core GC07 indicate a gradual warming from 11.5°C at 7.5 ± 0.2 ka to reach a maximum of 13.1°C at 4.2 ± 0.2 ka

Kusch et al., 2019

“High d13C values from Bliss Lake indicate that warmer conditions than today persisted from 7.2 to 6.5 cal. ka BP (Olsen et al. 2011). The records mentioned above imply relative warming during the HTM, but do not provide quantitative constraints on temperature changes. The closest terrestrial, non-ice-core record of absolute temperature change comes from Last Chance Lake in central East Greenland, approximately 1000 km farther south. Axford et al.(2017) D’Andrea et al. (2011) used the alkenone-basedUk’37 palaeothermometer to reconstruct lake water temperatures in two small lakes near Kangerlussuaq, southwest Greenland. Their results show variations of up to 5.5 °C since 5.6 cal. ka BP (D’Andrea et al. 2011). … Interestingly, using a combined MBT’/CBT calibration such as the Peterse et al. (2012) calibration (Table S1) results in a smoothed MAT curve, which shows a relatively constant ~3.7 °C decrease across the Holocene that agrees well with other temperature estimates (e.g. Axford et al. 2017).”

Jia et al., 2019

Joo et al., 2019

An early Holocene seawater temperature reconstruction for Dicksonfjorden exemplifies an amplified effect of warming (+4–6°C [warmer than present]) at high latitudes relative to global estimates (+1–3°C [warmer than present]; Beierlein et al. 2015). The early Holocene warmth culminated with a stepwise regional cooling, influenced by decreasing insolation, starting at ca. 9–8.8 Kya (Svendsen & Mangerud 1997; Hald et al. 2004; Forwick & Vorren 2009; Rasmussen et al. 2012; Mangerud & Svendsen 2018).”

Leopold et al., 2019

“The warmest phase, referred to as the ‘Holocene thermal optimum’, occurred around 10.7–7.7 kyr. BP, peaking at 10.2–9.2 kyr. BP (Mangerud and Svendsen 2018). Reconstructed summer SSTs were as high as 8 °C during this period and later dropped to around 4 °C where they stabilized and persisted for~ 5 kyr. (Sarnthein et al. 2003). … Even though the summer SSTs today around Svalbard are some 5–8 °C lower than during the thermal peak of the early Holocene, they are well within the temperature range when Mytilus spp. previously occupied the archipelago. The Holocene occurrence of Mytilus spp. was most likely a recurring event during intermittent warm periods (see Mangerud and Svendsen 2018, results and discussion).”

Brown et al., 2019

“While summers in the interior of BC were 2–4 ºC warmer-than-present (Rosenberg et al., 2004), the coastal regions were probably only 1–2 ºC warmer (Hebda, 1995; Mathewes and Heusser, 1981).”

Barhoumi et al., 2019

In North America and Arctic Canada, an early Holocene thermal maximum (from about 8000 to 5000 cal. yr BP) is evidenced with summer temperatures at least 2° warmer than today (Axford et al., 2009; Viau and Gajewski, 2009). In the prepolar and polar Ural regions, the climate was probably moist and warm (summer temperatures c. 4°C warmer than today) between 8000 and 4500 BP (Kultti et al., 2003).”

Valley et al., 2019

Bogren, 2019

“Macrofossil inferred temperatures from indicator plant taxa in northern Fennoscandia indicate that the very beginning of Holocene (between 11000 and 10000 cal. yr BP) had several degrees warmer summer temperatures than present (e.g. Valiranta et al., 2015; Shala et al., 2017), which is also in agreement with what Luoto et al. (2014) found in chironomid-based records in northern Finland.). … Most proxies indicate that a long-term cooling trend started in Fennoscandia during the late Holocene (from c. 5000 cal. yr BP to the present), likely related to the decreased insolation in northern Europe (Borzenkova et al., 2015). … In Abisko in the northern Swedish Scandes the tree-type Betula tree line is suggested to have been at an altitude of 300-400 m higher than present in the early Holocene (Barnekow, 1999; Barnekow and Sandgren, 2001).”

Schirrmacher et al., 2019

In the Gulf of Cádiz alkenone-based SST values vary between 20.0 to 22.7°C and are warmer compared to recent annual mean temperatures (18.7°C; Locarnini et al., 2013). Higher SSTs during the mid-Holocene might be partly a consequence of higher insolation during this period.”

Lin et al., 2019

The mid-Holocene period (MH) has long been an ideal target for the validation of general circulation model (GCM) results against reconstructions gathered in global datasets. Our results indicate that the main discrepancies between model and data for the MH climate are the annual and winter mean temperature. A warmer-than-present climate condition is derived from pollen data for both annual mean temperature ( 0.7 K on average) and winter mean temperature ( 1 K on average), while most of the models provide both colder-than-present annual and winter mean temperature and a relatively warmer summer, showing a linear response driven by the seasonal forcing.”

Cascella et al., 2019

Li and Born, 2019

D-O events could be an unforced oscillation of the Northern Seas coupled system … A sweet spot in the coupled system sets up feedbacks causing unforced oscillationsDansgaard-Oeschger events are most clearly seen in Greenland ice core records (Dansgaard et al., 1993; Andersen et al., 2004), where they represent temperature swings of 8–16°C (Severinghaus et al., 1998; Wolff et al., 2010). … Dansgaard-Oeschger events extend well beyond Greenland. Throughout the North Atlantic, observational evidence points to warmer ocean temperatures (Bond et al., 1993; Curry and Oppo, 1997), less sea ice (Masson-Delmotte et al., 2005; Rasmussen and Thomsen, 2004; Dokken et al., 2013), and fresher surface waters in the subtropical gyre (Schmidt et al., 2006). While the events themselves are millennial in time-scale, the transitions occur within decades or less, and the stadial-to-interstadial (cold-to-warm) transitions are more abrupt (Alley and Clark, 1999). Proxy evidence reveals that Dansgaard-Oeschger signals extended across the Northern Hemisphere and into the Southern Hemisphere.”

Bobylev and Miles, 2019

“The Holocene is the present interglacial period, which has persisted for about 12 kya. The Arctic summer air temperatures during the warmest part of the period were as much as 2–3°C above present for much of the region, which was well above the interglacial average temperature for the rest of Earth (Fig. 2.5). Multiple proxy records indicating that early Holocene temperatures were higher than today and that the Arctic contained less ice, are consistent with a high intensity of orbitally-controlled spring and summer insolation that peaked about 11 kya and gradually decreased thereafter. The warming phase after the end of the Younger Dryas was very abrupt and central Greenland temperatures increased by 7°C or more in a few decades (McBean et al. 2004). Arctic summer temperatures were warm enough to melt all glaciers below 5 km elevation, except the Greenland Ice Sheet, which was reduced moderately. The last major ice sheet disappeared from Scandinavia about 8000–7000 BC, while in North America the ice retreated completely at an even later date (Frolov et al. 2009). The continued Holocene climate warming, which culminated in the “Holocene Climatic Optimum” (HCO) of 5–9 kya, was characterized by a significant increase in mean air temperature, which was generally 2–3°C higher in summer compared to present conditions.”

Rohling et al., 2019

Røthe et al., 2019

“Our findings do not provide any confirmation that the glacier Sørfonna melted entirely away during the Holocene Thermal Maximum (HTM). Bjune et al. (2005) suggest summer temperatures were 1.5–2 °C warmer than present during this period. Combined with the evidence from the glaciers Nordfonna and Hardangerjøkulen, it is, however, likely that the glacier Sørfonnawas also significantly smaller than at present during this period. … Since 1650 cal. a BP, we infer that the glacier was larger than the 2002 CE glacier extent until 1910 CE when a GLOF [glacier outburst flood] occurred. Svartenutbreen has been retreating since 1910 CE, which led to the ice damming of the two historical GLOFs [glacier outburst floods] in the 1980s and 2002 CE separated by a glacier advance in the 1990s CE.”

Liu et al., 2019

“The modern vegetation around Tianchi Crater Lake is categorized as temperate mixed conifer-broad-leaved forest … The area experiences a typical cold temperate monsoon climatic regime with long cold winters and short cool summers. The [modern] annual average air temperature is 0–0.5 °C … The PFT-MAT-based reconstructed Pann record for Tianchi Crater Lake has a similar trend of variation to that of the pollen percentage diagram. The ranges of Pann [annual precipitation] and Tann [annual mean temperature] are 268–881 mm and 1.7–10.5°C, respectively [for the Holocene]. …[V]ariations in Tann exhibit […] a marked rise from the beginning of the early Holocene and a peak at 9000–8000 cal yr BP.”

Steinman et al., 2019

The early Holocene d18O [hydroclimate] maximum in the Castor Lake record at 9630 (9110-10,100) yr BP is likely in part a result of higher summer insolation, which produced higher temperatures and greater evaporation during the warm season. Additionally, atmospheric circulation in the early Holocene was substantially different from the modern configuration (Bartlein et al., 2014), and precipitation amounts were likely lower, due to the presence of the residual Laurentide and Cordilleran Ice Sheets (Dyke, 2004), which affected air mass trajectories and the seasonal distribution and amount of precipitation on a hemispheric scale. …  A chironomid based climate reconstruction from Windy Lake, south-central British Columbia, supports the assertion that greater summer insolation produced warmer summer temperatures at this time (Chase et al., 2008).”

Yan et al., 2019

High-precision uranium–thorium (U–Th) dating of dead branching corals from Luhuitou reef, Sanya, northern South China Sea (SCS) indicates that the reef framework grew episodically over the past 7,000 years. Episodes of coral reef growth (“switch-on” phases) occurred in response to regional warming during the mid-Holocene Climate Optimum, Medieval Warm Period and Current Warm Period, when the East Asian summer monsoon (EASM) was strong and the East Asian winter monsoon (EAWM) was weak. In contrast, episodes when reef growth dramatically slowed or ceased (“switch-off” phases) occurred during comparatively cold periods (e.g. Dark Age Cold Period and Little Ice Age), and are linked to abrupt weakening of the EASM and concurrent strengthening of the EAWM. … SST records derived from Sanya Porites coral cores dated from 6500 to 6100 yr BP indicate that the mid-Holocene maximum monthly summer SSTs during this period were as much as 2.0°C higher than at present in the northern SCS [South China Sea] [Wei et al., 2007]. … Reconstructions of SST based on Porites from the Leizhou Peninsula [Yu et al., 2005] indicate that while the summer SST maxima were relatively stable (~2°C) over the past 7,000 years, the winter SST minima displayed large variability (up to 5°C) between switch-off and switch-on episodes.

Zhang et al., 2019

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

Cao et al., 2019

Dauner et al., 2019

Lozhkin et al., 2019

“Mixed Larix-Betula forest was established at the Tanon site by ∼6600 14C BP (7500 cal BP). This forest included Betula platyphylla, a species common in moderate zones of the Russian Far East (e.g., B. platyphylla-Larix forests of central Kamchatka). The importance of Betula in the Middle Holocene assemblage is unusual, as tree Betula is not a common element in the modern coastal forest. The abundance of B. platyphylla macrofossils particularly suggests warmer than present summers and an extended growing period. This inference is supported by a regional climate model that indicates a narrow coastal region where the growing season was longer and summer temperatures were 2-4 °C warmer than today. Variations in Betula pollen percentages at other sites in northern Priokhot’ye are suggestive that this Middle Holocene forest was widespread along the coast.”

Novenko et al., 2019

[D]uring the Holocene Thermal Maximum when the mean annual temperatures were 2°С higher than those of the present day [6,9,10,11]. Roughly 5.7–5.5 ka BP, the Holocene Thermal Maximum was followed by gradual climatic cooling that included several warming and cooling phases with temperature fluctuations ranging between 2 and 3°С. …The CFSNBR [Central Forest State Natural Biosphere Reserve] is situated roughly 360 km northwest of Moscow (the Tver region, 56º35’ N, 32º55’ E) in an ecological zone transitioning from taiga to broadleaf forests. The vegetation of the CFSNBR is primary southern taiga forests, and it has been undisturbed by any human activities for at least 86 years. The climate of the study area is temperate and moderately continental with a mean annual temperature of 4.1°C and annual precipitation of roughly 700 mm.”

Rey et al., 2019

“Our results imply that mixed Fagus sylvatica forests with Abies alba and Quercus may re‐expand rapidly in these areas, if climate conditions will remain within the range of the midHolocene climatic variability (with summers c. +1–2°C warmer than today). … [T]he rise and fall of early farming societies was likely dependent on climate. Favourable climatic conditions (i.e. warm and dry summers) probably led to an increase in agricultural yields, the expansion of farming activities and resulting forest openings, whereas unfavourable climatic conditions (i.e. cold and wet summers) likely caused crop failures, abandonment of agricultural areas and forest succession. A better understanding of the environmental and societal factors controlling coeveal land-use dynamics as shown in this study would require new climate proxy data (e.g. temperature reconstruction from well dated and complete Holocene tree ring series). On the basis of our results and considering the ongoing spread of temperate forests in lowland Central Europe, we conclude that the existing beech forest ecosystems are resilient to anthropogenic disturbances under a changing climate.”

Eda et al., 2019

“Recent taxonomic composition and faunal distribution patterns support recognition of three biogeographic regions in Asia, Palaearctic (north), Indomalayan (south), and a transition zone between the two (Hoffmann 2001). In the division, the Yangtze River delta is located at the boundary of the Indomalayan region and transition zone. Pollen records suggest that, middle Holocene temperatures were ca. 2–4 °C warmer than today in the middle Yangtze River delta (Yi et al. 2003). Peters et al. (2016) indicated that the middle Yangtze River basin would delimit the northern most boundary for required habitat of (sub-) tropical red junglefowl during the Holocene thermal optimum. Furthermore, Xiang et al. (2014) reported that the wild distribution area of red junglefowl extended to northern China in the early Holocene, and domestic chicken farming began in the region.”

Caballero et al., 2019

“Diatom-based transfer functions for salinity, precipitation and temperature were developed using a training set that included data from 40 sites along central Mexico. … Maximum last glacial cooling of ∼5°C is reconstructed, a relatively wet deglacial and a warmer (+3.5°C [than present]) early Holocene. … The early Holocene marked a change towards high lake salinities and the highest positive temperature anomalies (+3.5°C) during a peak in summer insolation.”

Manzanilla-Quiñones et al., 2019 (North America)

“Given the recent diversification of the genus Abies in the world (Xiang et al., 2015), it is very likely that climatic conditions of 6 000 to 12 000 years ago were warmer (+2 °C) in North America’s temperate and cold areas (Caballero et al., 2010; Svensson et al., 2008).”

Helmens, 2019

“Quantitative climate reconstructions based on pollen from terrestrial plant taxa show mean July temperature values reaching 3 °C warmer than the present-day value of +13 °C at Sokli.”

Pei et al., 2019     

During the period of 0–10,000 yr BP, China’s temperature has closely followed the solar forcingThe correlation is as high as 0.800 (p < 0.01) for the EOF-based reconstruction. … Similar to the North Atlantic SST, AO also plays an important role in China’s temperature (Zuo et al., 2015). NAO and AO are both suggested to influence the climate in East Asia by modifying the strength and location of the 200 hPa jet stream (Yang et al., 2004). The AO record of Darby et al. (2012) is based on sea-ice drift, which has a high resolution of 10–100 years and shows a close connection with solar activities.”

Tanhuanpää et al., 2019

“The postglacial expansion of hazelnut happened in the Holocene epoch, mainly during the Sub-Boreal climatic stage about 6000–4000 years ago, when climate was 2–4 °C warmer than present (Eriksson et al. 1991).”

Ning et al., 2019

“Here we investigate the sources of branched glycerol dialkyl glycerol tetraethers (brGDGTs) in Lake Ximenglongtan from southwestern China and present a brGDGTs-based Holocene (~9.4 cal kyr BP) temperature reconstruction. Holocene temperature evolution is characterized by an early cool phase (with a mean annual air temperature (MAAT) of 12.5 °C) prior to 7.6 cal kyr BP, followed by a rapid warming towards the local thermal maximum (MAAT = 13.8 °C) from 7.6 to 5.5 cal kyr BP and a subsequent long-term cooling that ended at 1.5 cal kyr BP. Temperature changes after 1.5 cal kyr BP show high variability and low correspondence to global climate events such as the Medieval Warm Period. Overall Holocene temperature variation has been primarily controlled by boreal summer insolation changes.”

Rull et al., 2019 (Pantepui, NE South America)

“Myrica forests dominated during the HTM [Holocene Thermal Maximum] and reached their maximum importance at the end of this phase. A sudden replacement of these forests by tepui meadows dominated by Stegolepis took place after the HTM, just at the beginning of the regional cooling and drying trend initiated at B6 cal kyr BP. Myrica forests never returned to the site. The only species of this genus living today in the Guiana region, Myrica rotundata, is endemic to Pantepui and occurs on the slope forests of the Apakara´-tepui, with an upper distribution limit near the coring site (Miller, 2001). It has been suggested that during the HTM, warmer and wetter climates would have favored upslope migration of Myrica forests to higher elevations, which could explain their dominance in the Apakara´ summit. The subsequent post-HTM cooling would have returned Myrica to lower elevations favoring the local expansion of meadows. HTM climatic conditions never recovered during the rest of the Holocene, and Myrica remained at lower elevations until today (Rull and Montoya, 2017)”

Yuan et al., 2019

“During the early Holocene (10.0–6.0 ka), the modern-type circulation system was not established, which resulted in strong water column stratification; and the higher sea surface temperature (SST) might be associated with the Holocene Thermal Maximum (HTM). The interval of 6.0 to 1.0/2.0 ka displayed a weaker stratification caused by the intrusion of the Yellow Sea Warm Current (YSWC) and the initiation of the circulation system. A decreasing SST trend was related to the formation of the cold eddy generated by the circulation system in the ECS. During 1.0/2.0 to 0 ka, temperatures were characterized by much weaker stratification and an abrupt decrease of SST caused by the enhanced circulation system and stronger cold eddy, respectively.”

Marret et al., 2019

“The studied region is the only coastal region in Russia to have subtropical landscapes as well as humid to semi-arid landscapes (Petrooshina, 2003). Winter temperatures average 3–5°C in winter up to 23–24°C in summer. … A possible maximum of warm conditions may have occurred between 3.0 and 2.5 cal. ka BP, as highlighted by the occurrence of O. israelianum. This species has not been seen in modern sediments from the Black Sea nor the Caspian Sea and mainly occurs in waters where winter SSTs are above 14.3°C and summer SSTs are more than 24.2° C … Establishment of present-day conditions may have happened within the last 1500 years, but the low-resolution sampling at the top of the core prevents us to exactly pinpoint this change. However, our dinocyst assemblage indicates cooler conditions [today] with the decrease of S. mirabilis.”

Benson et al., 2019

“Summer temperatures reconstructed from Burial, Zagoskin, and Trout Lakes using fossil Chironomidae assemblages provide additional evidence of increased summer temperatures (Fig. 7) that were roughly 1–2°C warmer than modern July air temperatures (Kurek et al., 2009b; Irvine et al., 2012). Additional evidence suggesting regionally warm conditions during the early Holocene includes the highest rates of thaw-lake initiation and peat formation ages from 11 to 10 cal ka BP (Jones and Yu, 2010; Walter Anthony et al., 2014).”

Ortega et al., 2019

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

Hvidberg et al., 2019

“Here we present results from a study of the evolution of the Greenland ice sheet through the Holocene (Nielsen et al. 2018). We use a suite of different ice-core-derived climate histories for the Holocene to investigate the evolution of the Greenland ice sheet through the deglaciation, the Holocene thermal maximum and up to present day. The Holocene thermal maximum was a period 8–5 kyr ago when annual mean surface temperatures in Greenland were 2–3°C warmer than present-day values. We use climate histories based on new interpretations of the isotope records (Gkinis et al. 2014), which results in a more pronounced thermal maximum compared to previously used climate records. Furthermore, our records inform of snow accumulation rates in the early Holocene. Our studies show that the Greenland ice sheet retreated to a minimum volume of up to 1.2 m sea-level equivalent smaller than present in the early or mid-Holocene, and that the ice sheet has continued to recover from this minimum up to present day.”

Erturaç et al., 2019

Fletcher et al., 2019

The Pliocene is an intriguing climatic interval that offers important insights into climate feedbacks. Atmospheric CO2 concentrations were, at times, as high as modern ones (Fig. 1), but generally show a decreasing trend throughout the Pliocene (Haywood et al., 2016; Pagani et al., 2010; Royer et al., 2007; Stap et al., 2016), Although CO2 estimates from different methods do not converge, the modeled direct effects of these CO2 discrepancies appear to be small (Feng et al., 2017). Of additional importance for comparability to the modern climate system, continental configurations were similar to present (Dowsett et al., 2016). While global mean annual temperatures (MATs) during the Pliocene were only ∼ 3°C warmer than in the present day, Arctic land surface MATs may have been as much as 15 to 22°C warmer (Ballantyne et al., 2010; Csank et al., 2011a, b; Fletcher et al., 2017). Further, Arctic sea surface temperatures may have been as much as 10 to 15°C warmer than modern ones (Robinson, 2009), and sea levels were approximately 25 m higher than present (Dowsett et al., 2016). As a result, the Arctic terrestrial environment was significantly different from today, with boreal ecosystems at much higher latitudes (Salzmann et al., 2008).”

Feakins et al., 2019

At lake level [Lake Elsinore, southern California] mean annual temperature (MAT) averages 18°C, with summer average temperatures of 25°C, resulting in high potential evaporation rates and lake water loss of >1.4 m yr−1(Kirby et al., 2013). … [T]he reconstructed temperatures are reasonable with early Holocene values close to modern (18°C). … Temperatures >20°C are reported for six late glacial samples, including a high of 22°C at 29.4 ka and a maximum of 23°C at 26.8 ka which coincides with the pollen-inferred warm and dry period from 27.5–25.5 ka (Heusser et al., 2015) when the lake was shallow (∼3.2–4.5 m deep; Kirby et al., 2018). … The lowest temperature, 10°C, occurs at 23.5 ka and the deglacial warming from 14–12 ka is >10°C, agreeing with the pollen interpretations of ∼11°C warming at the glacial termination (Heusser et al., 2015).”

Klinge and Sauer, 2019

“For the Tsambagarav Mountain (central Mongolian Altai), Herren et al. (2013) reconstructed the climatic development over the last 6 ka, based on an ice core. Because the maximal age obtained for the base of the glacier ice was approximately 6 ka, they concluded that warm conditions led to disappearance of most of the glaciers in the Altai Mountains during the early to mid-Holocene. This assumption was supported by Ganyushkin et al. (2018), who found fossil wood above the modern tree line in the Mungun-Taiga Mountain in northwest Mongolia, dating between 10.6 ka and 6.2 ka. They concluded that the tree line was 350 m higher than today at that time, indicating that summer temperatures were 2.0-2.5°C warmer than at present, and MAP was about twice as much as today, which led to a decrease of the glaciated area.”

Axford et al., 2019

“Deltasø chironomids indicate peak early Holocene summer temperatures at least 2.5-3°C warmer than modern and at least 3.5-4°C warmer than the pre-industrial last millennium. We infer based upon lake sediment organic and biogenic content that in response to declining temperatures, North Ice Cap reached its present-day size ~1850 AD, having been smaller than present through most of the preceding Holocene.”

Jimenez-Moreno et al., 2019

“The pollen record is also consistent with higher than modern summer temperaturesPrevious studies from the area show that upper treeline would have been between 80 and 300 m higher than today. … Here, we find that low elevation thermophilous species, such as Quercus, Juniperus and Cercocarpus, reached maximum abundances between 8000 and 6700 cal yr BP in subzone EL-2a. This pattern probably points to the occurrence of these species at their highest Holocene elevations at this time and thus adds to evidence for the highest regional temperatures in the middle Holocene, possibly >2°C warmer than today (Andrews et al., 1975; Carrara et al., 1984; Elias, 1996).”

Reißig et al., 2019

“[T]he Tobago Basin core 235 subSSTMg/Ca record is highly variable and ranges from ~13-23°C, which is approximately three times as much as at Beata Ridge.. In Tobago Basin, the subSSTMg/Ca decrease by ~2°C from 30 ka BP (18°C) to the onset of HS1 (16°C). Within HS1, the subSSTMg/Ca increase continuously by 2°C, while at ~15.5 ka it rises abruptly by ~6°C up to maximum temperatures of 23°C. The abrupt subSST rise is delayed too the reconstructed SST rise at the beginning of HS1 by Bahr et al. (2018) (Fig. S7). Subsequently, subSSTMg/Ca scatters around 20°C until the beginning of the Bølling-Allerød (B/A). During the B/A and the YD the subSSTMg/Ca remains higher than ~19°C, abruptly increases up to ~22°C at mid YD, while steadily decreasing afterwards reaching modern values of ~15.5°C in the mid Holocene. Lowest subSSTMg/Ca of ~13°C are observed after ~7 ka BP. On average, the LGM subSSTMg/Ca are warmer by ~2.5°C than during the Holocene. … [T]he subsurface temperature variability is a robust climate signal in the tropical W Atlantic. Both records show an increase of ~5°C in subSSTMg/Ca from the LGM to the early YD and a subSSTMg/Ca decrease by ~7-8°C during the Holocene suggesting that both sediment cores are influenced by the same oceanographic changes. Notably, the mid Holocene subSSTMg/Ca in Tobago and Bonaire Basins remain cooler by ~1.5°C and ~3°C, respectively, than during the LGM. … At Tobago Basin and Bonaire Basin, the deglaciation is characterized by abrupt rises in subSSTMg/Ca by ~5.5°C at the end of HS1 and by ~6°C at the middle of the YD to peak values of up to ~23°C and ~22°C, respectively, accompanied by changes towards saline conditions (mean δ18Osw-ivf of ~2.25‰ and ~2‰, respectively (Fig. 3). These highly variable changes occur within less than 400 years. …  In contrast to modern conditions Tobago Basin core 235 was influenced by a warm water mass between 30-10 ka BP, indicated by elevated subSSTMg/Ca (~2.5°C warmer than the modern conditions)”

Yasuhara et al., 2019 

“Our reconstructions reveal a series of multi-centennial-scale abrupt warming events likely caused by upper NADW reduction coinciding with deglacial and Holocene stadial events. Notably, we discovered pervasive Holocene upper NADW variability in the western North Atlantic for at least the past 4000 yr and perhaps throughout the Holocene. Bottom-water temperature at ODP Site 1055 (1798 m) averaged ~5 °C during the last glacial period, which is slightly (by 1 °C) warmer than present-day and late Holocene values of ~4 °C. During the last deglaciation, ODP 1055 BWT shows several warming events supported by multiple data points (apart from noisy, singlepoint excursions). During the Holocene, ODP 1055 BWT shows ±1–1.5 °C multi-centennial-scale variability. Evidence for warmer-than-present lastglacial BWT at 1800 m water depth is consistent with low-resolution depth transect reconstructions (Dwyer et al., 2000).”

Colin et al., 2019   

The Holocene subpolar North Atlantic climate is characterized by an early to mid-Holocene “thermal maximum” followed byprogressive cooling induced by decreased insolation forcing (related to orbital precession) (e.g. Marchal et al., 2002; Sarnthein et al., 2003). This climatic cooling reflects a major reorganization of atmospheric and ocean circulation in the North Atlantic (e.g. O’Brien et al., 1995; Came and Oppo 2007; Repschlager et al., 2017).  … The time interval from 1 to 0.68 ka BP, which is marked by a strong eastward extension of the SPG, has been associated with the warm Medieval Climatic Anomaly and a subsequent intensification of the surface limb of the AMOC (Copard et al., 2012; Wanamaker et al., 2012; Ortega et al., 2015) (Fig. 4). The westward contraction of the weak SPG observed thereafter (between 0.68 and 0.2 ka BP) is coeval with the cold period of the Little Ice Age and may be linked to reduced AMOC intensity.”

Schweinsberg et al., 2019

Adamson et al., 2019

Wetterich et al., 2019  (NW Greenland)

“To reconstruct Holocene temperature changes, Lasher et al. (2017) employed δ18O of chironomid head capsules from Secret Lake in the Thule District as a proxy for the δ18O of precipitation, which is further related to surface air temperature. This proxy approach yields maximum estimates of Holocene temperature changes but is, as the study states, biased in summer and early autumn. The inferred summer season temperatures that were up to 4 °C warmer than today decreased from about 7.7 until about 2.3 ka cal BP before reaching colder than today temperatures, including the coldest period after about 1.2 ka cal BP (Lasher et al., 2017). The reconstructed period of decreasing summer temperatures covers the onset of permafrost aggradation at both sites, on Appat and at Annikitisoq, and likely relates to the dynamics of the NOW as reflected in sea surface temperature (SST), sea surface salinity (SSS), and sea ice cover (SIC) proxy data from marine sediments such as dinocyst records (Levac et al., 2001). After the breakup of perennial sea ice cover in the northern Baffin Bay around 10.5 ka cal BP, Holocene minima in SIC with up to 4–5 ice-free months per year occurred between about 7.4 and 4 ka cal BP accompanied by maxima in August SST and SSS (Levac et al., 2001).”

Bidauretta, 2019

Xu et al., 2019

Gebbie and Huybers, 2019

The ongoing deep Pacific is cooling, which revises Earth’s overall heat budget since 1750 downward by 35%. … In the deep Pacific, we find basin-wide cooling ranging from 0.02° to 0.08°C at depths between 1600 and 2800 m that is also statistically significant. The basic pattern of Atlantic warming and deep-Pacific cooling diagnosed from the observations is consistent with our model results, although the observations indicate stronger cooling trends in the Pacific. …. At depths below 2000 m, the Atlantic warms at an average rate of 0.1°C over the past century, whereas the deep Pacific cools by 0.02°C over the past century. … These basin-wide average trends are used to relax the assumption of globally uniform changes in surface conditions and to constrain regional temperature histories for 14 distinct regions over the Common Era by a control theory method. The result, referred to as OPT-0015, fits the observed vertical structure of Pacific cooling and Atlantic warming. Global surface changes still explain the basic Atlantic-Pacific difference in OPT-0015, but greater Southern Ocean cooling between 600 and 1600 CE leads to greater rates of cooling in the deep Pacific over recent centuries.”

Image Source: Supplemental Data (Gebbie and Huybers, 2019)

Svare, 2019 (Northern Europe)

“Seppä et al. (2008) set the summer temperature maximum in the northern European tree-line region to ca. 7500-6500 cal. yrs BP (ca. 1.5°C higher than present), similar to the Dovre area (Paus et al., 2011). Further, Bjune et al., (2005) found the HTM to last from ca. 8000 to 4000 cal. yrs BP in Western Norway, with temperatures reaching 12-13°C. … The early establishment of pine-forests in the area surrounding both study sites from ca. 9600 cal. yrs BP give evidence of local mean July temperatures of at least 11°C ca. 9600-8200 cal. yrs BP, 0.8-1.1°C warmer than present. From ca. 8200 cal. yrs BP until present day the July mean temperature has presumably been around 8-10°C.”

Recent (20th-21st Century) Cooling/Non-Warming

Sae-Lim et al., 2019

Klippel et al., 2019

[A]n analysis of instrumental temperatures for the period 1955–2013 shows that in northwestern Greece, statistically significant trends in summer temperature are absent (Feidas, 2016). The cooling trend from 1950–1976, previously reported throughout the Mediterranean basin, was followed by an, so far, insignificant warming (Piervitali et al., 1997; del Río et al., 2011). Our reconstruction mirrors this absence of a clear positive trend at decadal scale. … In total, 110 cold and 48 warm extremes appear in the 100SP reconstruction, and 105 cold and 57 warm extremes in the 10SP reconstruction (Figure 5 and Table S1). The year 1240 was the warmest summer, with reconstructed anomalies of +3.13 °C and +2.64 °C in the 100SP and 10SP reconstructions, respectively. The two coldest summers in the 100SP reconstruction are 1217 and 1884 with anomalies of –3.71 °C and –3.61 °C, respectively. The two coldest summers in the 10SP reconstruction occurred in different years, 1035 and 1117, with anomalies of –3.11 °C and -3.14°C, respectively. The third coldest summer in the 100SP and fourth coldest summer in the 10SP reconstructions, is 1959, which is the second coldest year in the instrumental EOBS v.15 record. The coldest decade is 1811–1820 (–0.73°C) and the warmest decade 1481–1490 (+0.88°C; calculated only for 100SP reconstruction). The elimination of decadal trends in the 10SP reconstruction causes events to appear more evenly distributed. However, over the past 450 years the occurrence of warm temperature extremes is substantially less frequent compared to preceding centuries.”

Borgaonkar, 2019

Ruan et al., 2019

Decelerated Greenland Ice Sheet Melt Driven by Positive Summer North Atlantic Oscillation … The GrIS lost mass at a rate of about -102 Gt/yr in early 2003, increased to -393 Gt/yr during 2012-2013, but suddenly reduced to no more than 75 Gt/yr during 2013-2014 (Bevis et al., 2019). It is suggested that this deceleration is due to the increased snowfall accumulation driven by the positive phase of summer North Atlantic Oscillation (sNAO; Folland et al., 2009; Chen et al., 2015). … It is shown that the deceleration of GrIS melting since 2013 is due to the reduction in short-wave solar radiation in the presence of increasing total cloud cover, which is driven by a more persistent positive summer North Atlantic Oscillation (sNAO) on the decadal time scale. … The lower SLP over Greenland is also consistent with the dramatic cooling of the northern North Atlantic Ocean during the same period. On the surface, the mean summer sea surface temperature (SST) in the North Atlantic subpolar gyre is more than 2ºC colder than the SST during 2003-2013; in the upper 300m, the volume mean ocean temperature is nearly 1.6ºC less (Fig. 6). The cooling of the ocean is not only helpful for the atmospheric configuration over the Greenland, but also favorable for the reduction of mass loss due to warmer water intrusion into the marine-terminated glaciers, though the latter process explains only around 30-50 Gt of the total mass budget of the GrIS (Zwally et al., 2002; Box et al., 2009; Tedstone et al., 2013).”

Caron et al., 2019

“Subzone 3b (2100 cal a BP to present; 45–0 cm) is characterized by the maximum abundance of I. minutum (up to 48%) and by increasing abundance of E. karaense, Polykrikos var. Arctic and cysts of P. dalei (Fig. 5). Sea‐surface reconstructions reveal a slight increase in SIC and a slight decrease in SST and primary productivity during this period. … In the Kane Basin, this transition toward interglacial conditions is also marked by the increase of accompanying autotrophic species O. centrocarpum and S. elongatus from 7880 to 7200 cal a BP, although the assemblage is still dominated by heterotrophic taxa. This suggests warmer sea‐surface conditions, which nonetheless remained relatively cold with an extended SIC, as expected considering the presence of the strong cold Arctic current flowing southward in the basin (Münchow et al., 2006). This is coherent with Levac et al. (2001), who suggest seasurface temperatures up to 3°C higher than at present as early as 7800 14C a BP (~8000 cal a BP) in Smith Sound.”

Nath and Luo, 2019

“Using the Community Earth System Model (CESM)-Large Ensemble (LE) surface air temperature (SAT) data, we investigate the multidecadal changes in SAT variability over Central Indian landmass, particularly the Indo-Gangetic (IG) river basin. This region comes under the active influence of the Indian summer monsoon, and during the summer monsoon months (JJA), we observe an amplified cooling (< − 3 °C) trend (1961–2000) in SAT. This SAT trend is considered as a superposition of external forcings and natural climatic variability. The forced response is computed by averaging the trend in 35 ensemble members, which displays a moderate cooling trend due to aerosol-, ozone-, and volcano-only forcings. But the internal variability introduces a wide range of uncertainties in SAT, with majority of the members display a strong cooling trend in the Central Indian region. During the entire period, natural climatic variability dominates over the forced response, which strongly overrides the greenhouse gas (GHG) warming. Here, we separate out the influence of global climate variability on regional climate variability and identify the specific internal variability which is responsible for the multidecadal cooling trend in the analyzed region.”

Toomey et al., 2019     

Caillouet et al., 2019

Booker et al., 2019

Warm Period 1 (~1924–2006 CE) was characterized by Tcal from 23 to 34°C (average 28.3 ± 0.96 °C), which is similar to the current seawater temperature for Grand Cayman and significantly warmer than CP 2. During this period there were two warm intervals (WI 2: ~1924–1932, WI 3: ~1972–1993) and two cool intervals (CI 3: ~1960–1972, CI 4: ~1993–2006). The warm intervals are characterized by an increase in Tcal of ~5–7 °C. The cool intervals are characterized by a decrease of ~4–5 °C. … • Mild Period 1 (~2006–2014 CE) was characterized by Tcal of 25 to 33 °C (average 27.5 ± 0.96 °C) which is similar to the current average seawater temperature for Grand Cayman (t-test: p b 0.01; Fig. 14).”

Campbell, 2019

Fröb et al., 2019

“The container vessel M/V Nuka Arctica, owned by Royal Arctic Line, operates between Ilulissaat, Greenland and Aalborg, Denmark. … The SST measurements on Nuka Arctica show a substantial cooling during winters between 2004 and 2017 (Figures 2c and S6). From the IRM-W through the ICE-W box, the SST trend varies between -0.084±0.020 and -0.096±0.018 ◦C yr−1. Towards the east, thecooling is less pronounced, and in the FB box, the SST trend is only -0.045±0.016 ◦C yr−1. Averaged over all boxes, SST decreased by 0.78±0.19◦C per decade.”

Watanabe et al., 2019

“[P]revious studies have observed that global surface air-temperatures remained relatively constant between the late-1990s and 2015, although climate models predicted continued anthropogenic warming. This so-called global-warming hiatus has received considerable attention [Kosaka et al., 2013]. Satellite-based SST data suggest that the main cause of the global-warming hiatus is the Interdecadal Pacific Oscillation (IPO), which is the dominant mode of atmosphere-ocean interactions in the subtropical Pacific. The IPO reversed from a positive to a negative phase in the late 1990s, i.e. the timing of the IPO phase change coincides with the onset of the global-warming hiatus. The negative IPO led to anomalous cooling in the eastern Pacific and this is thought to be a major cause of the global-warming hiatus. … The 26-year SSTanom record shows a significant regime shift in October 1996 (peak: 0.202; P < 0.01: Fig. 2b). The mean (range) of SSTanom is 0.73 ± 2.59 °C (10.96 °C) before 1996 and −0.46 ± 2.71 °C (11.72 °C) after 1996 (Fig. 2b). SST anom (δ18OSW-anom) shows a gradual cooling (decrease) over the past-26 years (−0.03 ± 0.01 °C/year and −0.02 ± 0.00‰VSMOW/year, respectively).”

Chen and Luo, 2019

Buckley et al., 2019

Li and Luo, 2019 (Eurasia)

The surface air temperature over the Eurasian continent has exhibited a significant cooling trend in recent decades (1990–2013), which has occurred simultaneously with Arctic warming and Arctic sea ice loss. While many studies demonstrated that midlatitude cold extremes are linked to Arctic warming and Arctic sea ice loss, some studies suggest that they are unrelated. The causal relationship between midlatitude cold extremes and Arctic change is uncertain, and it is thus an unsolved and difficult issue. … Arctic warming or sea ice decline is not necessary for the occurrence of midlatitude cold extremes.”

Holme et al., 2019

He et al., 2019

Lasher and Axford, 2019 (South Greenland)

More positive δ18O values are found between 900 and 1400 CE, indicating a period of warmth in South Greenland superimposed on late Holocene insolation-forced Neoglacial cooling, and thus not supporting a positive NAO anomaly during the MCA. Highly variable δ18O values record an unstable climate at the end of the MCA, preceding Norse abandonment of Greenland. The spatial pattern of paleoclimate in this region supports proposals that North Atlantic subpolar ocean currents modulated South Greenland’s climate over the past 3000 yr, particularly during the MCA. Terrestrial climate in the Labrador Sea and Baffin Bay regions may be spatially heterogeneous on centennial time scales due in part to the influence of the subpolar gyre.”

Zhang et al., 2019

“In core 31003, the SST record shows a distinctly anti-phase relationship with that of core 38002 over the last millennium. For instance, from the MWP to LIA, SST values increased from ∼17.0 ± 0.3°C to ∼19.1 ± 0.6°C in the northern core 38002 but decreased from ∼24.3 ± 0.4°C to ∼23.5 ± 0.3°C in the southern coastal core 31003. Since 1850 AD, the SST record in core 31003 elevated within the range of 24.3 ± 0.4°C, similar to values during the MWP, but decreased gradually to 18.0°C in core 38002, in line with the SST trends at two additional locations from the YSWC [Yellow Sea Warm Current] pathway as reported by He et al. (2014).”

Gräwe et al., 2019

MSLR [mean sea level rise] (corrected for the relative sea level contribution from GIA) in the Baltic Sea has been estimated by 2.08 ± 0.49 mm yr−1 over the period 1950–2015. This value is slightly larger than the simultaneous global mean of 1.63 ± 0.32 mm yr−1 (Dangendorf et al. 2017), as well as the adjacent southeastern North Sea (1.94 ± 0.36 mm yr−1 over 1940–2008; Albrecht et al. 2011).”

Porter et al., 2019

Byambaa et al., 2019     

[T]he recent cool-moist period from 1985 to 2000 has been related to the Arctic Oscillation (this study, Robock, 1984, He et al., 2017). The recent cooling could have been caused by volcanic aerosols of the El Chichón eruption (VEI5, 1982) in Southern Mexico, which impacted atmospheric wind patterns, including a positive phase of the Arctic Oscillation (Robock, 1984). No large volcanic-induced cooling was observed at this time due to the simultaneous warming ocean temperature caused by El-Niño (Robock, 2002). During this recent cool-moist period, ice mass accumulation of the glaciers in the Russian Altai Mountains was observed and Narozhniy and Zemtsov (2011) connected this phenomenon to annual precipitation increased by 8% – 10% especially in winter and spring (April-May) as a result of a strengthening of the zonal circulation over the Altai Mountains.”

Araźny et al., 2019

“Air temperature in 1899–1914 during three expeditions was 1.8–4.6 °C lower than the modern period in winter (Oct–Apr). However, during the 1930/31 expedition it was 4.6 °C warmer than the years 1981–2010. Our results relate to what has been called the ‘1930s warming’, referred to by various authors in the literature as the ETCW or the ETCAW. … In individual months, the highest negative anomalies were identified in Calm Bay (hereafter CB) in January 1914 (− 7.4 °C) and in February 1900 (− 6.8 °C). In contrast, during the 1930/31 expedition, it was 4.6 °C warmer than the present day in CB [Calm Bay]. Such a high thermal anomaly was influenced by a warm autumn and winter, especially February 1931, when the average monthly temperature was 10.7 °C higher than in the modern period.”

Huang et al., 2019

The temperature effect of the Zhada δ18OTR series is further verified by consistency with nearby ice-core δ18O variability.”

Huang et al., 2019

Climatic change is exhibiting significant effects on the ecosystem of the Tibetan Plateau (TP), a climate-sensitive area. In particular, winter frost, freezing events and snow avalanche frequently causing severe effects on ecosystem and social economy, however, few long-term winter temperature records or reconstructions hinder a better understanding on variations in winter temperature in the vast area of the TP. In this paper, we present a minimum winter (November–February) temperature reconstruction for the past 668 years based on a tree-ring network (12 new tree-ring chronologies) on the southeastern TP. The reconstruction exhibits decadal to inter-decadal temperature variability, with cold periods occurring in 1423–1508, 1592–1651, 1729–1768, 1798–1847, 1892–1927, and 1958–1981, and warm periods in 1340–1422, 1509–1570, 1652–1728, 1769–1797, 1848–1891, 1928–1957, and 1982–2007. … It also shows the possible effects of volcanic eruption and reducing solar activity on the winter temperature variability for the past six centuries on the southeastern TP.”

Vermassen  et al., 2019

“A link between the physical oceanography of West Greenland and Atlantic SSTs has indeed been suggested previously: a positive phase of the AMO [Atlantic Multidecadal Oscillation] is related to an increase of warm Atlantic waters flowing towards and along the SE and W Greenland shelf (Drinkwater et al., 2014; Lloyd et al., 2011). … Despite differences in the timing and magnitude of the retreat of the different glaciers, they broadly share the same retreat history. High retreat rates occurred between the mid ‘30s and mid ‘40s (400-800m/yr), moderate retreat rates between 1965-1985 (~200 m/yr, except for Upernavik) and high retreat rates again after 2000 (>200 m/yr). …  Since the meridional overturning circulation strength and associated heat transport is currently declining, (Frajka-Williams et al., 2017), this may lead to cooling bottom waters during the next decade in Upernavik Fjord and most likely also other fjords in West-Greenland.”


Kutta and Hubbart, 2019

Between 1900 and 2016, climatic trends were characterized by significant reductions in the maximum temperatures (−0.78°C/century; p = 0.001), significant increases in minimum temperatures (0.44 °C/century; p = 0.017) [overall -0.34°C per century], and increased annual precipitation (25.4 mm/century) indicative of a wetter and more temperate WV climate. Despite increasing trends of growing degree days during the first (p ≤ 0.015) and second half of the period of record, the long-term trend indicated a decrease in GDD [warm growing degree days] of approximately 100 °C/days.”

Lee et al., 2019

Eck et al., 2019

“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.”

Deng et al., 2019

“Recent SST records based on longchain alkenones imply that the MCA [Medieval Climate Anomaly] was slightly warmer than the CWP [Current Warm Period] in the northern SCS [South China Sea] (Kong et al., 2017).  … [I]t still should be noted that the SST record reconstructed from a Tridacna gigas Sr/Ca profile by Yan et al. (2015a) suggested that the annual average SST was approximately 0.89°C higher during the MCA [Medieval Climate Anomaly] than that of the CWP [Current Warm Period].”

Zhang et al., 2019

“Natural variability of Southern Ocean convection as a driver of observed climate trends … Observed Southern Ocean surface cooling and sea-ice expansion over the past several decades are inconsistent with many historical simulations from climate models. Here we show that natural multidecadal variability involving Southern Ocean convection may have contributed strongly to the observed temperature and sea-ice trends.”

Etourneau et al., 2019

“Based on water stable isotopes calibrated to recent air temperatures [Abram et al., 2013, Mulvaney et al., 2012], the reconstructed mean annual SAT documents a 1.5 °C cooling over the Holocene occurring in two steps between 10,000 and 6000 years before present (BP), and 3500 and 500 years BP. The Holocene cooling was interrupted by a slightly warmer period. The first main cooling episode corresponds to a phase of major EAP [East Antarctic Peninsula] ice shelf retreat reported in the literature [Domack et al., 2005, Cofaigh et al., 2014, Johnson et al., 2011, Davies et al., 2012]. … The Larsen A ice shelf was probably destabilized at least as early as ~6300 years BP [Brachfeld et al., 2003], while evidence show that the Larsen B ice shelf experienced a continuous and significant shrinkage throughout the Holocene [Domack et al., 2005]. Hence, the EAP ice shelves underwent a major retreat mostly between ~8000 and 6000 years BP. … [T]he ice core-derived SAT were overall warmer throughout the Holocene than during the last two millennia and could have hence favored the EAP [East Antarctic Peninsula] ice shelf surface melting during the entire period. … The long-term SOT [subsurface ocean temperatures] increasing trend at the JPC-38 core site was punctuated by up to 1.5 °C warm events at the centennial scale.”

Voelker et al., 2019

Gan et al., 2019

“Daily Minimum temperature (Tmin) is an important variable in both global and regional climate changes, and its variability can greatly affect the ecological system. In the early 21st century, warming slowdown is seen over the North Hemisphere and North America is one of the major cooling centers. … In this study, we found that Tmin experienced an obvious decline in North America during warming slowdown period. Such Tmin decline is closely related to the Atlantic Multidecadal Oscillation (AMO), the correlation between the decadal components of Tmin and AMO reached 0.71 during 1950-2014.”

Khazendar et al., 2019

“Jakobshavn Isbrae has been the single largest source of mass loss from the Greenland Ice Sheet over the last 20 years. During that time, it has been retreating, accelerating and thinning. Here we use airborne altimetry and satellite imagery to show that since 2016 Jakobshavn has been re-advancing, slowing and thickening. We link these changes to concurrent cooling of ocean waters in Disko Bay that spill over into Ilulissat Icefjord. Ocean temperatures in the bay’s upper 250 m have cooled to levels not seen since the mid 1980s. … Over the past several years, ocean temperatures have cooled on the continental shelf in the vicinity of Jakobshavn Isbrae . We find that ocean temperatures in Disko Bay below about 150 m cooled by nearly 2 °C between 2014 and 2016. …  The data then show cooling in the first half of 2016 of a normal magnitude (~2 °C) acting on water at already below-average temperatures cooling it to 1 °C, which is ~2–2.5 °C colder than the 2009–2015 values. The mooring data also show that temperatures remain significantly below average through summer 2017. … Since the late 1990s, Jakobshavn developed Greenland’s largest cumulative ice discharge anomaly, contributing the equivalent of ~0.9mm [9/100ths of a cm] to global mean sea-level rise between 2000 and 2010. … To explain the cooling observed in Davis Strait and in Disko Bay in 2015 and 2016, we first note that anomalous wintertime heat loss lowered ocean temperatures across the entire North Atlantic subpolar gyre since 2011 by about 0.6 °C on average in the top 300m of the water column (Supplementary Fig. 13). In the northern Irminger Sea where Atlantic Water first enters the East Greenland Current, ECCO shows that average temperatures have cooled by 0.75 °C over the same time period with the greatest cooling occurring during the winter of 2015. This 0.75 °C cooling of waters far upstream in the Irminger Sea explains part of the 2 °C cooling observed in Davis Strait and in Disko Bay. … Most prominently, the sharp drop in ocean temperatures in 2016 and 2017 by 2 °C relative to the peak temperature in 2014 corresponds to the slowing and dramatic thickening of the glacier in 2017 and 2018. The higher melting in 2014 simulated in our plume model is not reflected in flow acceleration and thinning, which we cannot explain.”

Zhou et al., 2019

These results demonstrated that the climate of the ASIR [the entire Antarctic Sea Ice Region, the (1) Weddell Sea (WS), (2) Indian Ocean, (3) Pacific Ocean (PO), (4) Ross Sea, and (5) Bellingshausen-Amundsen Sea (BS)] exhibits a cooling trend during summer [1982-2015], except for the BS. … Consistent with the trend of SAL [surface albedo], the slope values of SIC [sea ice concentration]  were mostly positive, except for the BS (Table 4), which further demonstrated that the climate of the ASIR exhibits a cooling trend in recent decades. … The average SAL (Table 3), SIC (Table 4), and SST (Table 5) for the total ASIR were 46.75%, 65.39%, and −2.44 °C during summer.”

Li et al., 2019

“On the contrary, there is a cooling trend by 0.29 ± 0.26 °C (10 yr)−1 in northern China during the recent 15 yr, where a warming rate about 0.38 ± 0.11 °C (10 yr)−1 happened for 1960–2000Overall, satellite simulation shows that the warming rate is reduced to −0.02 °C (10 yr)−1. The changes in underlying surface, Earth’s orbit, solar radiation and atmospheric counter radiation (USEOSRACR) cause China’s temperature rise about 0.02 °C (10 yr)−1. A combination of greenhouse gases (GHGs) and other natural forcing (ONAT, predominately volcanic activity, and atmosphere and ocean circulation) explain another part of temperature trend by approximately −0.04 °C (10 yr)−1. We conclude that there is a regional warming hiatus, a pause or a slowdown in China, and imply that GHGs-induced warming is suppressed by ONAT [other natural forcing] in the early 21st century.”

Jiang et al., 2019

“In this study, ring-width chronology of Picea jezoensis var. microsperma from the Changbai Mountain (CBM) area, Northeast China, was constructed. …  … The 11-year smoothing average of the reconstructed Tmax6–7 series was used to reveal low-frequency information and to show temperature variability in this area. After smoothing with an 11-year moving average, cold periods occurred in 1899–1913 (average value was 21.41 °C), 1955–1970 (21.49 °C), and 1975–1989 (20.97 °C), while warm periods occurred in 1881–1888 (23.93 °C). Furthermore, there are six obvious processes of Tmax6–7 increasing in 1781–1791 (from 22.76 °C to 23.54 °C), 1800–1809 (from 22.72 °C to 23.44 °C), 1835–1845 (from 22.66 °C to 23.76 °C), 1900–1919 (from 21.47 °C to 22.30 °C), 1931–1942 (from 21.36 °C to 22.04 °C), and 1983–2004 (from 20.49 °C to 22.99 °C), and five obvious processes of Tmax6–7 decreasing in 1790–1800 (from 21.89 °C to 22.98 °C), 1810–1835 (from 23.40 °C to 22.66 °C), 1880–1901 (from 23.83 °C to 21.25 °C), 1917–1931 (from 22.36 °C to 21.36 °C), and 1970–1983 (from 21.75 °C to 20.49 °C). In addition, the temperatures during 1780–1890 were much warmer (average value was 23.35 °C) than the temperatures during 1900–2004 (average value was 21.65 °C).”

Chafik et al., 2019     

After 2005, we observe a gradual transition from a weak to a strong subpolar gyre, which is related to the cooling and freshening trend of the SPNA.[Subpolar North Atlantic]. The anomalously low sea level during the past few winters (2014–2016) can be attributed to the exceptionally strong North Atlantic Oscillation and hence a return to the conditions seen during the early 1990s. We estimate the regional SPNA trend during the WP and CP to be about 3.9±1.5mm/yr and −7.1±1.3mm/yr, respectively. … Oceanic climate variability in the North Atlantic is known to be dominated by decadal-to-multidecadal fluctuations that have profound regional and global climate impacts. Recent observational evidence shows that the strength of the Atlantic Meridional Overturning Circulation or AMOC, i.e. the flow of warm surface waters polewards and the return of cold deep waters equatorwards, is indeed the major factor regulating the warm and cold decades of the North Atlantic as has long been hypothesized. This decadal-scale AMOC variability can have substantial influence on dynamical sea-level change, especially on regional scale, as a result of variable amount of mass, heat and freshwater redistributed by ocean currents.”

Kushnir and Stein, 2019

Medieval Climate in the Eastern Mediterranean: Instability and Evidence of Solar Forcing … The Nile summer flood levels were particularly low during the 10th and 11th centuries, as is also recorded in a large number of historical chronicles that described a large cluster of droughts that led to dire human strife associated with famine, pestilence and conflict. During that time droughts and cold spells also affected the northeastern Middle East, in Persia and Mesopotamia. Seeking an explanation for the pronounced aridity and human consequences across the entire EM, we note that the 10th–11th century events coincide with the medieval Oort Grand Solar Minimum, which came at the height of an interval of relatively high solar irradiance. Bringing together other tropical and Northern Hemisphere paleoclimatic evidence, we argue for the role of long-term variations in solar irradiance in shaping the early MCA in the EM and highlight their relevance to the present and near-term future.”

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