Opposing Trends of Winter Cold Extremes over Eastern Eurasia and North America under Recent Arctic Warming

Under recent Arctic warming,boreal winters have witnessed severe cold surges over both Eurasia and North America,bringing about serious social and economic impacts.Here,we investigated the changes in daily surface air temperature(SAT)variability during the rapid Arctic warming period of 1988/89–2015/16,and found the daily SAT variance,mainly contributed by the sub-seasonal component,shows an increasing and decreasing trend over eastern Eurasia and North America,respectively.Increasing cold extremes(defined as days with daily SAT anomalies below 1.5 standard deviations)dominated the increase of the daily SAT variability over eastern Eurasia,while decreasing cold extremes dominated the decrease of the daily SAT variability over North America.The circulation regime of cold extremes over eastern Eurasia(North America)is characterized by an enhanced high-pressure ridge over the Urals(Alaska)and surface Siberian(Canadian)high.The data analyses and model simulations show the recent strengthening of the high-pressure ridge over the Urals was associated with warming of the Barents–Kara seas in the Arctic region,while the high-pressure ridge over Alaska was influenced by the offset effect of Arctic warming over the East Siberian–Chukchi seas and the Pacific decadal oscillation(PDO)–like sea surface temperature(SST)anomalies over the North Pacific.The transition of the PDO-like SST anomalies from a positive to negative phase cancelled the impact of Arctic warming,reduced the occurrence of extreme cold days,and possibly resulted in the decreasing trend of daily SAT variability in North America.The multi-ensemble simulations of climate models confirmed the regional Arctic warming as the driver of the increasing SAT variance over eastern Eurasia and North America and the overwhelming effect of SST forcing on the decreasing SAT variance over North America.Therefore,the regional response of winter cold extremes at midlatitudes to the Arctic warming could be different due to the distinct impact of decadal SST anomalies.

Frequent central Pacific La Nina events may accelerate Arctic warming since the 1980s

Including significant warming trend,Arctic climate changes also exhibit strong interannual variations in various fields,which is suggested to be related to El Nino and Southern Oscillation(ENSO)events.Previous studies have demonstrated the different impacts on the Arctic of central Pacific(CP)and eastern Pacific(EP)ENSO events,and suggested these impacts are largely of opposite sign for ENSO warm and cold phases.Our results illustrate asymmetrical changes for the cold and warm ENSO events,especially for the La Nina events.Compared to the past frequent basin-wide cooling La Nina events,since the 1980 s the cooling center for the La Nina event has strengthened and moved westward along with the increasing frequency for the canonical and CP La Nina events.Contrary to the basin-wide cooling and canonical La Nina events,the frequent CP La Nina events induce significant warming from the Beaufort Sea to Greenland via the convection center moving northward over the western Pacific.Observation analysis and numerical experiments both suggest that the changes in La Nina type may also accelerate Arctic warming.

Arctic warming and its influence on East Asian winter cold events:a brief recap

The rate of warming of Arctic surface temperature is about 2–3 times faster than the global mean surface warming. Increases of ice albedo feedback and water vapor as well as moisture intrusion from outside the Arctic all have major roles in this phenomenon. In contrast to this rapid Arctic warming, in recent decades, stronger cold air outbreaks have occurred more frequently during winter in East Asia than were recorded in the 1990s, resulting in severe socioeconomic impacts. A number of related studies have claimed the increased frequency of these stronger cold air outbreaks is linked to the amplified warming in the Arctic through complicated mechanisms. As there are time lags between the observed Arctic warming and East Asian cold weather response at various scales, understanding the entire chain of processes from the Arctic to East Asia has importance for forecasting winter weather in East Asia. There are two pathways linking Arctic warming with East Asian cold weather events. One is the synoptic-scale pathway in the lower troposphere via strengthening of the Siberian High initiated by Ural blocking. The other is the planetary-scale path through the stratosphere via activation of planetary waves and downward propagation, which weakens the polar vortex. This study briefly reviews the current understanding of the linkage mechanisms between Arctic warming and East Asian winter cold weather.

Arctic warming trends and their uncertainties based on surface temperature reconstruction under different sea ice extent scenarios

IPCC AR6 states that the neglect of recent rapid warming in the Arctic generally leads to an underestimate of global warming trends.In this study,by reconstructing the surface temperature(ST)datasets in the Arctic under different sea ice extent scenarios(Imax and Imin),we respectively evaluated the annual and seasonal warming trends and their uncertainties from 1900 to 2020.The results show that the reconstructed datasets have a good representation of the ST change trends in the Arctic.In 1900e2020,the annual warming trends in the Arctic(0.17±0.031 and 0.14±0.025℃ per decade under the Imax and Imin reconstruction,respectively)are roughly 1.6e1.8 times the global mean warming trends(0.10±0.008 and 0.09±0.008℃ per decade).While in 1979e2020,the Arctic warming trends(0.66±0.100 and 0.55±0.080℃ per decade)increase to 3.1e3.5 times of the global warming trend(0.19±0.023 and 0.18±0.023℃ per decade)for Imax and Imin,respectively,indicating that the Arctic amplification effect has been significantly enhancing in recent decades.Although the seasonal warming trends are closely related to cloud feedback mechanisms,atmospheric circulation,and ocean circulation,they are not sensitive to the different reconstruction scenarios.

An Interdecadal Change in the Influence of the NAO on Atlantic-Induced Arctic Daily Warming around the Mid-1980s

After approaching 0℃owing to an Atlantic storm at the end of 2015,the Arctic temperature approached freezing again in 2022,indicating that Arctic daily warming events remain a concern.The NCEP/NCAR Reanalysis dataset was used to investigate the influence of the NAO on the Arctic winter daily warming events induced by Atlantic storms,known as the Atlantic pattern-Arctic Rapid Tropospheric Daily Warming(Atlantic-RTDW)event.Atlantic-RTDW events are triggered by Atlantic storms that transport warm and humid air masses moving into the Arctic.Furthermore,an interdecadal change in the influence of NAO on Atlantic-RTDW-event frequency was observed around the mid-1980s.Specifically,before the mid-1980s(pre-transition period),500-hPa southerly(northerly)wind anomalies occupied the North Atlantic(NA)in the positive(negative)phase of NAO,which increased(decreased)the Atlantic-RTDW events occurrence by steering Atlantic storms into(away from)the Arctic;thus,the NAO could potentially influence the Atlantic-RTDW-event frequency.However,the relationship between the NAO and the Atlantic-RTDW-event frequency has weakened since the mid-1980s(post-transition period).In the post-transition period,such 500-hPa southerly(northerly)wind anomalies over the NA hardly existed in the positive(negative)phase of NAO,which was attributed to a stronger Atlantic Storm Track(AST)activity intensity than that in the pre-transition period.During this period,the strong AST induced an enhanced NAOrelated cyclone via transient eddy-mean flow interactions,resulting in the disappearance of southerly and northerly wind anomalies over the NA.

The 2020/21 Extremely Cold Winter in China Influenced by the Synergistic Effect of La Niña and Warm Arctic

In the first half of winter 2020/21,China has experienced an extremely cold period across both northern and southern regions,with record-breaking low temperatures set in many stations of China.Meanwhile,a moderate La Niña event which exceeded both oceanic and atmospheric thresholds began in August 2020 and in a few months developed into its mature phase,just prior to the 2020/21 winter.In this report,the mid−high-latitude large-scale atmospheric circulation anomalies in the Northern Hemisphere,which were forced by the negative phase of Arctic Oscillation,a strengthened Siberian High,an intensified Ural High and a deepened East Asian Trough,are considered to be the direct reason for the frequent cold surges in winter 2020/21.At the same time,the synergistic effect of the warm Arctic and the cold tropical Pacific(La Niña)provided an indispensable background,at a hemispheric scale,to intensify the atmospheric circulation anomalies in middle-to-high latitudes.In the end,a most recent La Niña prediction is provided and the on-coming evolution of climate is discussed for the remaining part of the 2020/21 winter for the purpose of future decision-making and early warning.

Inferring future warming in the Arctic from the observed global warming trend and CMIP6 simulations

The emergent constraint approach is a way of using multi-model ensembles to identify the linkage between current/past climate variability and future climate changes,which has been widely used for narrowing down the uncertainty of multi-model projections of future climate change.Climate models of the latest Coupled Model Intercomparison Project Phase 6(CMIP6)show a much stronger Arctic wanning signal but with a larger inter-model spread.In this study,we find that the projected Arctic warming made by multi-models in CMIP6 is positively correlated with the simulated global warming trend during the period of 1981-2011 in historical runs.This enables us to tighter constraints to future warming in the Arctic by using the observed global warming during the instrument era.The fact that CMIP6 models tend to overestimate the trend of global mean surface temperature during 1981-2011,therefore,would imply a relative weak Arctic warming compared to the CMIP6 median warming projection.

As the Arctic Warms

冰雪皑皑的北极现正在逐步变暖,这不仅对全球气温产生影响,更危害到了生活在北极的动物,如北极熊和其他哺乳动物等。本文为美国北极气候影响评估中心最新的调查报告,通过数据揭示了发生在北极的变化。