A panda attempting to keep cool during the summer 2011 heat wave in Chengdu, China. Photo Credit: Z. Liu/China News Service.

Anomalous weather events such as heat waves and droughts have occurred more frequently in the mid-latitudes of Eurasia and North  America during recent summers, coincident with record losses of Arctic sea ice and early-summer snow cover on northern high-latitude land. There is a connection between the vanishing cryosphere, shifting summer weather patterns, and more frequent extreme heat events over mid-latitude continents, according to a new international study.

Prof. TANG Qiuhong’s group from the Institute of Geographic Sciences and Natural Resources Research (IGSNRR), Chinese Academy of Sciences (CAS), in collaboration with Research Professor Jennifer A. Francis of Rutgers University, combined satellite observations of snow cover and Arctic sea-ice extent with atmospheric reanalysis data to demonstrate the linkages between summer weather patterns in mid-latitudes and cryosphere loss.

They found that the response of atmospheric circulation to sea-ice loss was stronger than that to snow melt. Accompanying the vanishing cryosphere is a changing jet stream: weakened west-to-east winds and a general northward shift. Consequently, the atmospheric circulation change tends to favor more persistent weather systems and a higher likelihood of summer weather extremes.

“Previous studies have shown that rapid sea-ice loss affects winter weather patterns and cold extremes in the mid-latitudes. However, the mechanisms that may relate the melting cryosphere with extreme heat events in summer remain unclear,” says lead-author TANG Qiuhong of IGSNRR, CAS. “The study contributes to a growing body of evidence that in addition to its effect on high-latitude environments, the melting Arctic has wide-ranging implications for people living in the middle latitudes.”

“It’s interesting to know the connection between our weather here and losses of ice and snow thousands of miles away,” adds co-author ZHANG Xuejun, a first-year PhD student in TANG Qiuhong’s group at IGSNRR, CAS. As the Earth is a complex and coupled system, saving the environment around you may help reduce climate change and slow the increase in extreme weather events.

Co-author Jennifer Francis explains, “The difference in temperature between the high and middle latitudes is what drives the jet stream, a fast-moving river of air that encircles the northern hemisphere. As the high latitudes warm faster than the mid-latitudes because of amplifying effects of melting ice, the west-to-east jet-stream wind is weakened. The weaker winds cause the jet stream to meander more northward and southward, which causes the eastward progression of those waves to slow. Because jet-stream waves control the formation and movement of storms, slower wave progression means that weather conditions will be more persistent.”

As Arctic and global warming continue unabated and the cryosphere continues to disappear, this study suggests more summer heat extremes in the major population centers across much of North America and Eurasia where billions of people live will likely become more frequent.