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This study investigates the physical mechanisms that contributed to the 2016 Eurasian heat wave during boreal summer season (July-August, JA), characterized by much higher than normal temperatures over eastern Europe, East Asia, and the Kamchatka Peninsula. It is found that the 2016 JA mean surface air temperature, upper-tropospheric height, and soil moisture anomalies are characterized by a tri-pole pattern over the Eurasia continent and a wave train-like structure not dissimilar to recent (1980-2016) trends in those quantities. A series of forecast experiments designed to isolate the impacts of the land, ocean, and sea ice conditions on the development of the heat wave is carried out with the Global Seasonal Forecast System version 5. The results suggest that the tri-pole blocking pattern over Eurasia, which appears to be instrumental in the development of the 2016 summer heat wave, can be viewed as an expression of the recent trends, amplified by record-breaking oceanic warming and internal land-atmosphere interactions.

This paper presents Atmospheric Infra-Red Sounder (AIRS) surface skin temperature anomalies for the period 2003 through 2017, and compares them to station-based analyses of surface air temperature anomalies (principally the Goddard Institute for Space Studies Surface Temperature Analysis (GISTEMP)). The AIRS instrument flies on EOS Aqua, which was launched in 2002 and became stable in September 2002. AIRS surface temperatures are completely satellite-based and are totally independent of any surface-based measurements. We show in this paper that satellite-based surface temperatures can serve as an important validation of surface-based estimates and help to improve surface-based data sets in a way that can be extended back many decades to further scientific research. AIRS surface temperatures have better spatial coverage than those of GISTEMP, though at the global annual scale the two data sets are highly coherent. As in the surface-based analyses, 2016 was the warmest year yet.

This paper reviews and analyses the past 20 years of change and variability of European mountain permafrost in response to climate change based on time series of ground temperatures along a south-north transect of deep boreholes from Sierra Nevada in Spain (37°N) to Svalbard (78°N), established between 1998 and 2000 during the EU-funded PACE (Permafrost and Climate in Europe) project. In Sierra Nevada (at the Veleta Peak), no permafrost is encountered. All other boreholes are drilled in permafrost. Results show that permafrost warmed at all sites down to depths of 50 m or more. The warming at a 20 m depth varied between 1.5 °C on Svalbard and 0.4 °C in the Alps. Warming rates tend to be less pronounced in the warm permafrost boreholes, which is partly due to latent heat effects at more ice-rich sites with ground temperatures close to 0 °C. At most sites, the air temperature at 2 m height showed a smaller increase than the near-ground-surface temperature, leading to an increase of surface offsets (SOs). The active layer thickness (ALT) increased at all sites between c. 10% and 200% with respect to the start of the study period, with the largest changes observed in the European Alps. Multi-temporal electrical resistivity tomography (ERT) carried out at six sites showed a decrease in electrical resistivity, independently supporting our conclusion of ground ice degradation and higher unfrozen water content.

A regional, 175 year long, tree-ring width chronology (spanning 1840–2014 C.E.) was developed for Pinus wallichiana A. B. Jacks. (Himalayan Blue pine) from the Lidder Valley, Kashmir, Northwest Himalaya. Simple and seasonal correlation analysis (SEASCORR) with monthly climate records demonstrates a significant direct positive relationship of tree growth with winter temperature. A linear regression model explains 64% of the total variance of the winter temperature and is used to reconstruct December–March temperatures back to 1855 C.E. The most noticeable feature of the reconstruction is a marked warming trend beginning in the late twentieth century and persisting through the present. This reconstruction was compared with instrumental records and other proxy based local and regional temperature reconstructions and generally agrees with the tree-ring records and is consistent with the marked loss of glacial ice over the last few decades. Spectral analysis reveals a periodicity likely associated with the Atlantic Multidecadal Oscillation and El Niño–Southern Oscillation. Spatial correlation patterns of sea surface temperatures with the observed and reconstructed winter temperatures are consistent with larger scale warming in the region.

Seasonal differences of temperature are crucial components of the Earth’s climate system. However, the relatively short observational record, especially for East Asia, has limited progress in understanding seasonal differences. In this study, we identify ten tree-ring chronologies separately correlated with local winter (December–February) temperatures and twelve different tree-ring chronologies separately correlated with summer (June–August) temperatures across East Asia. Using these discrete seasonal tree-ring chronologies, we develop two independent winter and summer temperature reconstructions covering the period 1376–1995 CE for East Asia, and compare them with model simulations. Our reconstructions show a more significant volcanic cooling and earlier onset of modern warming in summer than in winter. The reconstructed summer-minus-winter temperature decreased since as early as the late 19th century, which has driven the current state of seasonal temperature difference to out of the natural variability since the 1370s. Climate models could generally reproduce the variability and trends in seasonal reconstructions, but might largely underestimate seasonal differences due to the fact that seasonal expressions on external forcing and modes of internal variability are too small. Our study highlights the importance of using proxy-based seasonal reconstructions to evaluate the performance of climate models, and implies a substantial weakening of seasonal temperature differences in the future.

In this study, we constructed a ring-width chronology derived from Betula ermanii (BE) near the transitional zone between forests and tundra within the Changbai Mountain (CBM) region. This chronology was established utilizing 55 cores obtained from 30 trees. Our analysis of growth/climate responses underscores the pivotal role of the mean maximum winter temperature in influencing radial growth. Drawing upon these growth/climate associations, we reconstructed the mean maximum temperature series for December of the preceding year through January of the current year for the years 1787 and 2005 CE, employing a standardized chronology. During the calibration period (1960–2005), the reconstructed series exhibited an explained variance of 36%. This reconstruction provides crucial insights into historical temperature fluctuations within the study area. Our findings indicate that year-to-year temperature variations did not manifest synchronously along the altitude gradient of Changbai Mountain. Notably, the response to recent winter warming exhibited disparities with the altitude on Changbai Mountain. Specifically, the higher altitude range (1950–2000 m a.s.l.) displayed a response to warming around 1960, the mid-altitude range (765–1188 m a.s.l.) responded around 1975, and the lowest altitude (650 m a.s.l.) responded by 1977. Consequently, the paleotemperature research outcomes from Changbai Mountain alone may not adequately characterize climate change in this region. We recommend future high-resolution temperature records be obtained through sampling at various altitudes to enhance the comprehensiveness of our understanding.

The environmental system of the northern Nordic Seas is very sensitive to oceanographic and climatic changes at the contact of cold Arctic and warmer North Atlantic waters. These contrasts are reflected in the associations of marine microorganisms and archived in the bottom sediments. A microfossil study (diatoms, coccoliths) of late Holocene sediments in core MSM5/5-712-1 from the eastern Fram Strait provides a better understanding of marine ecosystems and palaeoenvironments during Arctic warming events of the last two millennia. Indicative diatom species and groups of species revealed a high variability of sea-surface conditions. Based on the diatom distribution, three warming periods could be detected, corresponding to the time intervals of 0 to 440 CE (the later part of the Roman Warm Period), 1200 to1420 CE (the final part of the Medieval Climate Anomaly) and 1730 CE to present (including the Recent Warming). The various micropalaeontological proxies used in this study and other publications describe the Roman Warm Period and, especially, the Recent Warming as the most pronounced warm events in the area during the last 2000 years. A comparison of data from the different microfossil groups, indicators of sea-surface and subsurface conditions, reveals variable, complicated and non-simultaneous palaeoenvironmental signals within the warm periods. This can potentially be explained by changes in the surface/subsurface water structure during the events (variations in the cold/warm water advection, stratification, availability of nutrients, seasonal succession of bioproductivity, etc.), which are reflected by changes in the microplankton communities.

The Antarctic Peninsula has warmed faster than the global average rate of warming during the last century. Due to limited availability of long term meteorological records, the geographical extent of this rapid warming is poorly defined. We collected borehole temperature measurements in the upper 300 m of Rutford Ice Stream, West Antarctica, and employed an inverse modeling scheme with a heat diffusion‐advection equation to determine the recent surface temperature history of the borehole position. Our results reveal recent warming of 0.17 ± 0.07°C (decade)−1 since 1930. This result suggests that, at least in an attenuated form, the rapid warming observed over the Antarctic Peninsula extends as far south as Rutford Ice Stream. This result agrees with other recent results that show a warming trend across much of the West Antarctic Ice Sheet.

Reconstruction of temporal and spatial climate development on a seasonal basis during the last few centuries may help us better understand modern-day interplay between natural and anthropogenic climate variability. The objective of this paper is to reconstruct hydrology and landscape changes of East Siberia during the termination of the Little Ice Age and the subsequent Recent Warming. We analysed sediment samples from the saltwater Sulfatnoe Lake, Bolshoye Alginskoe and freshwater Shuchie Lake using high-resolution X-ray fluorescence spectroscopy at 1-mm scan resolution, Fourier-transform infrared techniques and pollen analyses. The depth–age models of the cores were constructed by ²¹⁰Pb activity using the constant rate of supply model. The lake sediment cover of these lakes began to form from ca. 1870. Three significant periods (1870–1895, 1895–1925 and from 1925 to the present) were defined in hydrology and chemical regime of these lakes for the past 140 years. Lake levels were extremely low and high saturated with salts during the final period of the Little Ice Age. Lake levels began to slowly rise from 1870 to 1895 and vegetation was poor at that period. Intensive desalination of the lakes occurred in 1895–1925, and environment conditions were temperate and favourable for the majority of the taxa of the regional vegetation. Regional precipitation significantly increased and water saturation of the catchments was high from 1925 to the present. The chemical precipitation of carbonate stopped completely in Lake Shichie and reduced considerably in Lake Sulfatnoe and B. Alginskoe. Strong increasing trend of weathering of the lake catchments began in 1970 and still continues.

The Sun has surely been a major external forcing to the climate system throughout the Holocene. Nevertheless, opposite trends in solar radiation and temperatures have been empirically identified in the last few decades. Here, by means of an inferential method-the Granger causality analysis-we analyze this situation and, for the first time, show that an evident causal decoupling between total solar irradiance and global temperature has appeared since the 1960s.