Warming Since The Mid/Late 20th Century?
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.
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.
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.
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.
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.
A Warmer Past, Non-Hockey Stick Reconstructions
Magyari et al., 2018 …its 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).
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).
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.
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).
Lack Of Anthropogenic/CO2 Signal In Sea Level Rise
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.
Sea Levels 1-3 Meters Higher Than Present 4,000-7,000 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.
A Model-Defying Cryosphere, Polar Ice
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.