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The ability of our ancestors to switch food sources and to migrate to more favourable environments enabled the rapid global expansion of anatomically modern humans beyond Africa as early as 120,000 years ago. Whether this versatility was largely the result of environmentally determined processes or was instead dominated by cultural drivers, social structures, and interactions among different groups, is unclear. We develop a statistical approach that combines both archaeological and genetic data to infer the more-likely initial expansion routes in northern Eurasia and the Americas. We then quantify the main differences in past environmental conditions between the more-likely routes and other potential (less-likely) routes of expansion. We establish that, even though cultural drivers remain plausible at finer scales, the emergent migration corridors were predominantly constrained by a combination of regional environmental conditions, including the presence of a forest-grassland ecotone, changes in temperature and precipitation, and proximity to rivers. Past global human migration was the result of environmental and cultural factors. Here, the authors develop a statistical approach that combines archaeological, genetic, and palaeoclimate data to identify regional environmental conditions facilitating population expansion routes in northern Eurasia and the Americas. [ABSTRACT FROM AUTHOR]

Archaeological evidence attests multiple early dispersals of Homo sapiens out of Africa, but genetic evidence points to the primacy of a single dispersal 70-40 ka. Laili in Timor-Leste is on the southern dispersal route between Eurasia and Australasia and has the earliest record of human occupation in the eastern Wallacean archipelago. New evidence from the site shows that, unusually in the region, sediment accumulated in the shelter without human occupation, in the window 59–54 ka. This was followed by an abrupt onset of intensive human habitation beginning ~44 ka. The initial occupation is distinctive from overlying layers in the aquatic focus of faunal exploitation, while it has similarities in material culture to other early Homo sapiens sites in Wallacea. We suggest that the intensive early occupation at Laili represents a colonisation phase, which may have overwhelmed previous human dispersals in this part of the world. Archaeological and genetic evidence suggest differing scenarios for human migration out of Africa. Here, the authors present archaeological evidence of intense occupation in Wallacea from 44 thousand years ago, suggesting that this occupation obscured genetic evidence of earlier dispersals. [ABSTRACT FROM AUTHOR]

The origins and dispersal of the chicken across the ancient world remains one of the most enigmatic questions regarding Eurasian domesticated animals. The lack of agreement concerning timing and centers of origin is due to issues with morphological identifications, a lack of direct dating, and poor preservation of thin, brittle bird bones. Here we show that chickens were widely raised across southern Central Asia from the fourth century BC through medieval periods, likely dispersing along the ancient Silk Road. We present archaeological and molecular evidence for the raising of chickens for egg production, based on material from 12 different archaeological sites spanning a millennium and a half. These eggshells were recovered in high abundance at all of these sites, suggesting that chickens may have been an important part of the overall diet and that chickens may have lost seasonal egg-laying The origin and dispersal of the chicken across Eurasia is unclear. Here, the authors examine eggshell fragments from southern Central Asia with paleoproteomics to identify chicken eggshells, suggesting that chickens may have been an important dietary component as early as 400BCE. [ABSTRACT FROM AUTHOR]

The summer Eurasian westerly jet is reported to become weaker and wavier, thus promoting the frequent weather extremes. However, the primary driver of the changing jet stream remains in debate, mainly due to the regionality and seasonality of the Eurasian jet. Here we report a sharp increase, by approximately 140%, in the interannual variability of the summertime East Asian jet (EAJ) since the end of twentieth century. Such interdecadal change induces considerable changes in the large-scale circulation pattern across Eurasia, and consequently weather and climate extremes including heatwaves, droughts, and Asian monsoonal rainfall regime shifts. The trigger mainly emerges from preceding February North Atlantic seesaw called Scandinavian pattern (contributing to 81.1 ± 2.9% of the enhanced EAJ variability), which harnesses the "cross-seasonal-coupled oceanic-atmospheric bridge" to exert a delayed impact on EAJ and thus aids relevant predictions five months in advance. However, projections from state-of-the-art models with prescribed anthropogenic forcing exhibit no similar circulation changes. This sheds light on that, at the interannual timescale, a substantial portion of recently increasing variability in the East Asian sector of the Eurasian westerly jet arises from unforced natural variability. The summer jet stream above East Asia has become more variable in recent decades, leading to weather and climate extremes across Eurasia. The authors show that a Scandinavian Pattern in preceding February is driving the strong variability. [ABSTRACT FROM AUTHOR]

The Holocene temperature conundrum, the discrepancy between proxy-based Holocene global cooling and simulated global annual warming trends, remains controversial. Meanwhile, reconstructions and simulations show inconsistent spatial patterns of terrestrial temperature changes. Here we report Holocene alkenone records to address spatial patterns over mid-latitude Eurasia. In contrast with long-term cooling trends in warm season temperatures in northeastern China, records from southwestern Siberia are characterized by colder conditions before ~6,000 years ago, thus long-term warming trends. Together with existing records from surrounding regions, we infer that colder airmass might have prevailed in the interior of mid-latitude Eurasian continent during the early to mid-Holocene, perhaps associated with atmospheric response to remnant ice sheets. Our results challenge the proposed seasonality bias in proxies and modeled spatial patterns in study region, highlighting that spatial patterns of Holocene temperature changes should be re-considered in record integrations and model simulations, with important implications for terrestrial hydroclimate changes. New alkenone results and existing temperature records together show contrasting Holocene temperature trends and thus display spatial patterns over mid-latitude Eurasia, with implications for the Holocene temperature conundrum. [ABSTRACT FROM AUTHOR]

The Cenozoic India-Eurasia collision has had profound impacts on shaping the Tibetan plateau, but its early history remains controversial due to uneven availability of constraints. Recent plate reconstructions reveal two prominent counterclockwise rotation (azimuthal change) rate peaks of the Indian plate at 52-44 and 33-20 Ma, respectively, which could bear key information about this collision history. Using fully dynamic three-dimensional numerical modeling, we show that the first rotation rate peak reflected the initial diachronous collision from the western-central to eastern Indian front, and the second peak reflected the full collision leading to strong coupling between India and Eurasia. Further comparison with observation suggests that the initial and complete India-Eurasia collision likely occurred at 55 ± 5 and 40 ± 5 Ma, respectively, an inference consistent with key geological observations. We suggest that this collision history is instructive for studying the tectonic history of the Tibetan plateau and its surrounding areas. Dynamic 3D modelling of counterclockwise rotation of the Indian plate, which peaked at 52-44 and 33-20 Ma, reveals the diachronous India-Eurasia collision from western-centre to east since 55 ± 5 Ma and complete collision since 40 ± 5 Ma. [ABSTRACT FROM AUTHOR]

The Qinghai-Tibet Plateau (QTP), possesses a climate as cold as that of the Arctic, and also presents uniquely low oxygen concentrations and intense ultraviolet (UV) radiation. QTP animals have adapted to these extreme conditions, but whether they obtained genetic variations from the Arctic during cold adaptation, and how genomic mutations in non-coding regions regulate gene expression under hypoxia and intense UV environment, remain largely unknown. Here, we assemble a high-quality saker falcon genome and resequence populations across Eurasia. We identify female-biased hybridization with Arctic gyrfalcons in the last glacial maximum, that endowed eastern sakers with alleles conveying larger body size and changes in fat metabolism, predisposing their QTP cold adaptation. We discover that QTP hypoxia and UV adaptations mainly involve independent changes in non-coding genomic variants. Our study highlights key roles of gene flow from Arctic relatives during QTP hypothermia adaptation, and cis-regulatory elements during hypoxic response and UV protection. The Qinghai-Tibet Plateau is as cold as the Arctic, but presents unique hypoxia and high ultraviolet conditions. Here the authors find that gene flow from Arctic gyrfalcons aids plateau saker falcons' cold adaptation, and independent non-coding genomic changes underlie hypoxic and ultraviolet responses. [ABSTRACT FROM AUTHOR]

Northern Hemisphere forests changed drastically in the early Eocene with the diversification of the oak family (Fagaceae). Cooling climates over the next 20 million years fostered the spread of temperate biomes that became increasingly dominated by oaks and their chestnut relatives. Here we use phylogenomic analyses of nuclear and plastid genomes to investigate the timing and pattern of major macroevolutionary events and ancient genome-wide signatures of hybridization across Fagaceae. Innovation related to seed dispersal is implicated in triggering waves of continental radiations beginning with the rapid diversification of major lineages and resulting in unparalleled transformation of forest dynamics within 15 million years following the K-Pg extinction. We detect introgression at multiple time scales, including ancient events predating the origination of genus-level diversity. As oak lineages moved into newly available temperate habitats in the early Miocene, secondary contact between previously isolated species occurred. This resulted in adaptive introgression, which may have further amplified the diversification of white oaks across Eurasia. Fagaceae are diverse family including trees of ecological and economic importance. This phylogenomic analysis of nuclear and plastid genomes reconstructs evolutionary history and finds evidence of multiple adaptive introgression events in this important plant family. [ABSTRACT FROM AUTHOR]

Frequency and intensity of warm and moist air-mass intrusions into the Arctic have increased over the past decades and have been related to sea ice melt. During our year-long expedition in the remote central Arctic Ocean, a record-breaking increase in temperature, moisture and downwelling-longwave radiation was observed in mid-April 2020, during an air-mass intrusion carrying air pollutants from northern Eurasia. The two-day intrusion, caused drastic changes in the aerosol size distribution, chemical composition and particle hygroscopicity. Here we show how the intrusion transformed the Arctic from a remote low-particle environment to an area comparable to a central-European urban setting. Additionally, the intrusion resulted in an explosive increase in cloud condensation nuclei, which can have direct effects on Arctic clouds' radiation, their precipitation patterns, and their lifetime. Thus, unless prompt actions to significantly reduce emissions in the source regions are taken, such intrusion events are expected to continue to affect the Arctic climate. Warm and moist air-mass intrusions into the Arctic are more frequent than the past decades. Here, the authors show that warm air mass intrusions from northern Eurasia inject record amounts of aerosols into the central Arctic Ocean strongly impacting atmospheric chemistry and cloud properties. [ABSTRACT FROM AUTHOR]

Transmission-driven multi-/extensively drug resistant (M/XDR) tuberculosis (TB) is the largest single contributor to human mortality due to antimicrobial resistance. A few major clades of the Mycobacterium tuberculosis complex belonging to lineage 2, responsible for high prevalence of MDR-TB in Eurasia, show outstanding transnational distributions. Here, we determined factors underlying the emergence and epidemic spread of the W148 clade by genome sequencing and Bayesian demogenetic analyses of 720 isolates from 23 countries. We dated a common ancestor around 1963 and identified two successive epidemic expansions in the late 1980s and late 1990s, coinciding with major socio-economic changes in the post-Soviet Era. These population expansions favored accumulation of resistance mutations to up to 11 anti-TB drugs, with MDR evolving toward additional resistances to fluoroquinolones and second-line injectable drugs within 20 years on average. Timescaled haplotypic density analysis revealed that widespread acquisition of compensatory mutations was associated with transmission success of XDR strains. Virtually all W148 strains harbored a hypervirulence-associated ppe38 gene locus, and incipient recurrent emergence of prpR mutation-mediated drug tolerance was detected. The outstanding genetic arsenal of this geographically widespread M/XDR strain clade represents a "perfect storm" that jeopardizes the successful introduction of new anti-M/XDR-TB antibiotic regimens. An outbreak of the multidrug-resistant Mycobacterium tuberculosis lineage W148 has spread widely across Russia, Central Asia and Europe. Here, the authors use whole genome sequences of ~700 isolates of this lineage collected over ~20 years to analyze its spread, evolution of drug resistance, and impact of compensatory mutations. [ABSTRACT FROM AUTHOR]

Spinescence is an important functional trait possessed by many plant species for physical defence against mammalian herbivores. The development of spinescence must have been closely associated with both biotic and abiotic factors in the geological past, but knowledge of spinescence evolution suffers from a dearth of fossil records, with most studies focusing on spatial patterns and spinescence-herbivore interactions in modern ecosystems. Numerous well-preserved Eocene (~39 Ma) plant fossils exhibiting seven different spine morphologies discovered recently in the central Tibetan Plateau, combined with molecular phylogenetic character reconstruction, point not only to the presence of a diversity of spiny plants in Eocene central Tibet but a rapid diversification of spiny plants in Eurasia around that time. These spiny plants occupied an open woodland landscape, indicated by numerous megafossils and grass phytoliths found in the same deposits, as well as numerical climate and vegetation modelling. Our study shows that regional aridification and expansion of herbivorous mammals may have driven the diversification of functional spinescence in central Tibetan woodlands, ~24 million years earlier than similar transformations in Africa. Spines are an important physical defense for many plant species. Here, the authors describe seven different spine morphologies from the Eocene of central Tibet associated with regional aridification and expansion of herbivorous mammals. [ABSTRACT FROM AUTHOR]

Winter surface air temperature (Tas) over the Barents–Kara Seas (BKS) and other Arctic regions has experienced rapid warming since the late 1990s that has been linked to the concurring cooling over Eurasia, and these multidecadal trends are attributed partly to internal variability. However, how such variability is generated is unclear. Through analyses of observations and model simulations, we show that sea ice–air two-way interactions amplify multidecadal variability in sea-ice cover, sea surface temperatures (SST) and Tas from the North Atlantic to BKS, and the Atlantic Meridional Overturning Circulation (AMOC) mainly through variations in surface fluxes. When sea ice is fixed in flux calculations, multidecadal variations are reduced substantially (by 20–50%) not only in Arctic Tas, but also in North Atlantic SST and AMOC. The results suggest that sea ice–air interactions are crucial for multidecadal climate variability in both the Arctic and North Atlantic, similar to air-sea interactions for tropical climate. Sea ice–air interactions greatly amplify multidecadal variability in Arctic air temperatures and sea ice cover, North Atlantic sea surface temperatures, and Atlantic meridional overturning circulation through changes in surface fluxes. [ABSTRACT FROM AUTHOR]

Annual-to-decadal variability in northern midlatitude temperature is dominated by the cold season. However, climate field reconstructions are often based on tree rings that represent the growing season. Here we present cold-season (October-to-May average) temperature field reconstructions for the northern midlatitudes, 1701-1905, based on extensive phenological data (freezing and thawing dates of rivers, plant observations). Northern midlatitude land temperatures exceeded the variability range of the 18th and 19th centuries by the 1940s, to which recent warming has added another 1.5 °C. A sequences of cold winters 1808/9-1815/6 can be explained by two volcanic eruptions and unusual atmospheric flow. Weak southwesterlies over Western Europe in early winter caused low Eurasian temperatures, which persisted into spring even though the flow pattern did not. Twentieth century data and model simulations confirm this persistence and point to increased snow cover as a cause, consistent with sparse information on Eurasian snow in the early 19th century. A cold season climate reconstruction for the northern midlatitudes based on freezing and thawing dates of rivers shows a cold spell 1808/9-1815/6 affecting Eurasia. In addition to two volcanic eruptions, increased snow cover played an important role. [ABSTRACT FROM AUTHOR]

Northern Hemisphere forests changed drastically in the early Eocene with the diversification of the oak family (Fagaceae). Cooling climates over the next 20 million years fostered the spread of temperate biomes that became increasingly dominated by oaks and their chestnut relatives. Here we use phylogenomic analyses of nuclear and plastid genomes to investigate the timing and pattern of major macroevolutionary events and ancient genome-wide signatures of hybridization across Fagaceae. Innovation related to seed dispersal is implicated in triggering waves of continental radiations beginning with the rapid diversification of major lineages and resulting in unparalleled transformation of forest dynamics within 15 million years following the K-Pg extinction. We detect introgression at multiple time scales, including ancient events predating the origination of genus-level diversity. As oak lineages moved into newly available temperate habitats in the early Miocene, secondary contact between previously isolated species occurred. This resulted in adaptive introgression, which may have further amplified the diversification of white oaks across Eurasia. Fagaceae are diverse family including trees of ecological and economic importance. This phylogenomic analysis of nuclear and plastid genomes reconstructs evolutionary history and finds evidence of multiple adaptive introgression events in this important plant family. [ABSTRACT FROM AUTHOR]

Despite tectonic conditions and atmospheric CO2 levels (pCO2) similar to those of present-day, geological reconstructions from the mid-Pliocene (3.3-3.0 Ma) document high lake levels in the Sahel and mesic conditions in subtropical Eurasia, suggesting drastic reorganizations of subtropical terrestrial hydroclimate during this interval. Here, using a compilation of proxy data and multi-model paleoclimate simulations, we show that the mid-Pliocene hydroclimate state is not driven by direct CO2 radiative forcing but by a loss of northern high-latitude ice sheets and continental greening. These ice sheet and vegetation changes are long-term Earth system feedbacks to elevated pCO2. Further, the moist conditions in the Sahel and subtropical Eurasia during the mid-Pliocene are a product of enhanced tropospheric humidity and a stationary wave response to the surface warming pattern, which varies strongly with land cover changes. These findings highlight the potential for amplified terrestrial hydroclimate responses over long timescales to a sustained CO2 forcing. In contrast to future projections, paleoclimate records often find wetter subtropics in tandem with elevated CO2. Here, a compilation of proxies and simulations are used to reveal the climate dynamics and feedbacks responsible for generating wet subtropics during the mid-Pliocene. [ABSTRACT FROM AUTHOR]

We developed a method, ArchaicSeeker 2.0, to identify introgressed hominin sequences and model multiple-wave admixture. The new method enabled us to discern two waves of introgression from both Denisovan-like and Neanderthal-like hominins in present-day Eurasian populations and an ancient Siberian individual. We estimated that an early Denisovan-like introgression occurred in Eurasia around 118.8–94.0 thousand years ago (kya). In contrast, we detected only one single episode of Denisovan-like admixture in indigenous peoples eastern to the Wallace-Line. Modeling ancient admixtures suggested an early dispersal of modern humans throughout Asia before the Toba volcanic super-eruption 74 kya, predating the initial peopling of Asia as proposed by the traditional Out-of-Africa model. Survived archaic sequences are involved in various phenotypes including immune and body mass (e.g., ZNF169), cardiovascular and lung function (e.g., HHAT), UV response and carbohydrate metabolism (e.g., HYAL1/HYAL2/HYAL3), while "archaic deserts" are enriched with genes associated with skin development and keratinization. Existing methods to identify the presence of DNA from other hominin species can be limited in the ability to accurately estimate introgression waves, or can only be applied to specific populations. Here, the authors have developed a generalizable method to identify introgression in multi-wave situations. [ABSTRACT FROM AUTHOR]

After the main Out-of-Africa event, humans interbred with Neanderthals leaving 1–2% of Neanderthal DNA scattered in small fragments in all non-African genomes today. Here we investigate what can be learned about human demographic processes from the size distribution of these fragments. We observe differences in fragment length across Eurasia with 12% longer fragments in East Asians than West Eurasians. Comparisons between extant populations with ancient samples show that these differences are caused by different rates of decay in length by recombination since the Neanderthal admixture. In concordance, we observe a strong correlation between the average fragment length and the mutation accumulation, similar to what is expected by changing the ages at reproduction as estimated from trio studies. Altogether, our results suggest differences in the generation interval across Eurasia, by up 10–20%, over the past 40,000 years. We use sex-specific mutation signatures to infer whether these changes were driven by shifts in either male or female age at reproduction, or both. We also find that previously reported variation in the mutational spectrum may be largely explained by changes to the generation interval. We conclude that Neanderthal fragment lengths provide unique insight into differences among human populations over recent history. Historical interbreeding between Neanderthals and humans should leave signatures of historical demographics in modern human genomes. Analysing the size distribution of Neanderthal fragments in non-African genomes suggests consistent differences in the generation interval across Eurasia, and that this could explain mutational spectrum variation. [ABSTRACT FROM AUTHOR]

The peopling of Sahul (the combined continent of Australia and New Guinea) represents the earliest continental migration and settlement event of solely anatomically modern humans, but its patterns and ecological drivers remain largely conceptual in the current literature. We present an advanced stochastic-ecological model to test the relative support for scenarios describing where and when the first humans entered Sahul, and their most probable routes of early settlement. The model supports a dominant entry via the northwest Sahul Shelf first, potentially followed by a second entry through New Guinea, with initial entry most consistent with 50,000 or 75,000 years ago based on comparison with bias-corrected archaeological map layers. The model's emergent properties predict that peopling of the entire continent occurred rapidly across all ecological environments within 156–208 human generations (4368–5599 years) and at a plausible rate of 0.71–0.92 km year−1. More broadly, our methods and approaches can readily inform other global migration debates, with results supporting an exit of anatomically modern humans from Africa 63,000–90,000 years ago, and the peopling of Eurasia in as little as 12,000–15,000 years via inland routes. Advanced ecological modelling reveals how Sahul (Australia and New Guinea) was first peopled, suggesting the most probable routes and surprisingly rapid early settlement of this continent by anatomically modern humans starting 50,000 to 75,000 years ago. [ABSTRACT FROM AUTHOR]

The European steppes and their biota have been hypothesized to be either young remnants of the Pleistocene steppe belt or, alternatively, to represent relicts of long-term persisting populations; both scenarios directly bear on nature conservation priorities. Here, we evaluate the conservation value of threatened disjunct steppic grassland habitats in Europe in the context of the Eurasian steppe biome. We use genomic data and ecological niche modelling to assess pre-defined, biome-specific criteria for three plant and three arthropod species. We show that the evolutionary history of Eurasian steppe biota is strikingly congruent across species. The biota of European steppe outposts were long-term isolated from the Asian steppes, and European steppes emerged as disproportionally conservation relevant, harbouring regionally endemic genetic lineages, large genetic diversity, and a mosaic of stable refugia. We emphasize that conserving what is left of Europe's steppes is crucial for conserving the biological diversity of the entire Eurasian steppe biome. Europe hosts isolated remnants of the steppe belt that once covered much of Eurasia. Here the authors combine genomic data and ecological niche modelling on three plant and three insect species to show evolution independent of the zonal steppe and high conservation value of these extrazonal steppes. [ABSTRACT FROM AUTHOR]

Neanderthals and modern humans both occupied the Levant for tens of thousands of years prior to the spread of modern humans into the rest of Eurasia and their replacement of the Neanderthals. That the inter-species boundary remained geographically localized for so long is a puzzle, particularly in light of the rapidity of its subsequent movement. Here, we propose that infectious-disease dynamics can explain the localization and persistence of the inter-species boundary. We further propose, and support with dynamical-systems models, that introgression-based transmission of alleles related to the immune system would have gradually diminished this barrier to pervasive inter-species interaction, leading to the eventual release of the inter-species boundary from its geographic localization. Asymmetries between the species in the characteristics of their associated 'pathogen packages' could have generated feedback that allowed modern humans to overcome disease burden earlier than Neanderthals, giving them an advantage in their subsequent spread into Eurasia. Modern humans and Neanderthals coexisted in the Levant for tens of thousands of years before modern humans spread and replaced Neanderthals. Here, Greenbaum et al. develop a model showing that transmission of disease and genes can explain the maintenance and then collapse of this contact zone. [ABSTRACT FROM AUTHOR]

The Montreal Protocol has succeeded in limiting major ozone-depleting substance emissions, and consequently stratospheric ozone concentrations are expected to recover this century. However, there is a large uncertainty in the rate of regional ozone recovery in the Northern Hemisphere. Here we identify a Eurasia-North America dipole mode in the total column ozone over the Northern Hemisphere, showing negative and positive total column ozone anomaly centres over Eurasia and North America, respectively. The positive trend of this mode explains an enhanced total column ozone decline over the Eurasian continent in the past three decades, which is closely related to the polar vortex shift towards Eurasia. Multiple chemistry-climate-model simulations indicate that the positive Eurasia-North America dipole trend in late winter is likely to continue in the near future. Our findings suggest that the anticipated ozone recovery in late winter will be sensitive not only to the ozone-depleting substance decline but also to the polar vortex changes, and could be substantially delayed in some regions of the Northern Hemisphere extratropics. [ABSTRACT FROM AUTHOR]

Winter Eurasian cooling after the mid-1990s has been verified by numerous studies, although in recent decades, the mid-latitudes of the Northern Hemisphere have been rapidly warming globally. Because the cooling is not uniform at different spatial and temporal scales, over time, this change may not truly reflect the nature of climate fluctuations. Here, by using three types of data (reanalysis, weather station, and remote sensing image data) to assess variations in Eurasian seasonal cooling, we examine the causes of these changes. During a 30-year climatology (1989–2018), we show that a significant (P < 0.05) abrupt change in the autumn Eurasian air temperature trend occurred in 2003. Our results suggest that from 2004–2018, the autumn Eurasian temperature reveals a significant cooling trend (P < 0.05). We demonstrate that the autumn cooling in Eurasia is likely influenced by the Pacific Decadal Oscillation (PDO) and Siberian high (SH). Since 2004, the strengthening of the PDO and SH explains approximately 54% and 18% of the autumn cooling in Eurasia, respectively. We also find that the cooling in autumn is stronger than that in winter. In the last years, an extensive winter cooling over central Eurasia has been discussed widely. Here, the authors show that from 2004–2018, the Eurasian cooling in autumn is stronger than that in winter, and that this autumn cooling is likely influenced by the Pacific Decadal Oscillation and the Siberian high. [ABSTRACT FROM AUTHOR]

Eurasian continent has experienced cold winters over the past two decades in contrast with Arctic warming. Previous studies have suggested that the cold Eurasian winters are associated with Arctic sea-ice loss, while others attributed them to atmospheric internal variability. However, here we show that the Arctic and Eurasian climate linkage is driven by the combination between atmospheric teleconnection originating in the tropical oceans and Arctic sea ice. Like a battery charges a capacitor, El Niño heats the tropical Atlantic, and the warmer Atlantic condition persists until early winter of El Niño-decay year. We find that the persisting tropical Atlantic warming induces anomalous Rossby wave train arching to Eurasia, leading to Arctic sea-ice increase and Eurasian warming. In La Niña phase these changes are reversed. Our results therefore suggest that the combination of recent tropical Pacific cooling and Arctic sea-ice loss have contributed to the frequent Eurasian cold winters. El Niño warms the tropical Atlantic, which in turn induces an anomalous Rossby wave train, triggering Arctic sea-ice growth and Eurasian warming in the El Niño decay year. This teleconnection via the tropical Atlantic and the Arctic in La Niña decay year contributes to Eurasian cold winter extremes. [ABSTRACT FROM AUTHOR]