The Arctic has warmed about 2 to 3 times faster than the rest of world for the past several decades, a phenomenon known as Arctic amplification. In contrast to this rapid Arctic warming, northern continents have, in recent years, experienced prolonged cold spells and severe snow events that have had significant socioeconomic impacts, including upticks in cold-related casualties as well as lengthy shutdowns of businesses, schools, and airports that have slowed economies and left students and travelers stranded. There is thus an urgent need for better physical understanding and prediction of these winter extremes.
A debate has lingered among scientists over whether recent cold anomalies over Northern Hemisphere midlatitudes are linked with Arctic warming. One school of thought claims that reductions in Arctic sea ice have, by impacting Arctic temperatures and the polar jet stream, led to statistically robust cold anomalies over the midlatitudes. Others suggest that recent cold events are driven only by natural midlatitude climate variability rather than by changes in external forcing. Motivated by this scientific controversy, as well as by the recognition that recent cold anomalies have had a strong regional preference for East Asia, the Arctic Warming and East Asia Weather Linkage Workshop was held at the Korea Polar Research Institute in Incheon, South Korea, on 13 May 2019.
The most important and controversial questions addressed at the workshop had to do with the robustness of the relationship between Arctic warming and East Asian cold anomalies as well as potential causal mechanisms for this relationship. The following are some of the notable points that meeting participants discussed:
- At least 44% of recent winter Eurasian cooling is attributable to the sea ice loss over the Barents and Kara Seas, but current state-of-the-art models underestimate East Asian cooling related to sea ice loss.
Troposphere-stratosphere coupling is critical in understanding the Arctic–East Asia weather linkage, but the processes and pathways by which this coupling occurs are not well understood.
- Variations in tropical sea surface temperatures play a critical role in modulating sea ice in the Arctic, which is, in turn, one of the main drivers of midlatitude weather.
- In diagnosing atmospheric responses to Arctic amplification, air pressures at sea level may not be an ideal metric. Instead, the thickness of the lower troposphere (between about 1,000 and 500 hectopascals) might be a better metric.
- The linkage between Arctic warming and cold anomalies in East Asia has a multidecadal behavior—with weaker relations from 1901 to 1929 and 1955 to 1979 and stronger relations from 1930 to 1954 and 1989 to 2013—associated with long-term variations in climatological stationary waves originating from the North Atlantic.
- Current coupled models suffer in simulating observed Arctic-midlatitude linkages because they include feedbacks from the ocean, which are still not well known and thus not well modeled. One needs to interpret model results with care.
- The lasting effect, or memory, of changes to high-latitude land surfaces, such as increased snow cover caused by Arctic amplification, on conditions in subsequent months and years should be considered in models.
- Arctic warming not only modulates winter weather but is also linked to extreme summer heat waves in East Asia. However, understanding summer Arctic–East Asia weather linkages is in an incipient stage, and the mechanism behind the summer linkage remains unclear.
This was the first meeting about the Arctic–East Asia weather linkage issue with participants from East Asian countries. The workshop led to a clearer picture of the connection between Arctic change and extreme weather in East Asia. However, many aspects of the linkage remain unclear. To continue in-depth discussions, participants agreed to plan another meeting in the near future.
—Seong-Joong Kim ([email protected]), Division of Polar Climate Sciences, Korea Polar Research Institute, Incheon, South Korea; Baek-Min Kim, Department of Environmental Atmospheric Sciences, Pukyong National University, Busan, South Korea; and Jinro Ukita, Faculty of Science, Niigata University, Niigata, Japan