More Frequent Atmospheric Rivers Are Hindering the Recovery of Arctic Sea Ice
Sea ice off the Alaskan village of Kotzebue. (Courtesy Lamont-Doherty Earth Observatory)
The Arctic is rapidly losing sea ice, even during winter months, when temperatures are below freezing and ice must be recovering from the summer melt. Now, a latest study within the journal Nature Climate Change has found that powerful storm systems called atmospheric rivers are partly responsible; the study finds they’re increasingly reaching the Arctic in winter, slowing sea ice recovery and accounting for a 3rd of all winter sea ice decline.
“Arctic sea ice decline is amongst probably the most obvious evidence of world warming from the past several a long time,” said lead creator Pengfei Zhang of Penn State University. “Despite temperatures within the Arctic being well below freezing, sea ice decline in winter remains to be very significant. And our research shows atmospheric rivers are one think about understanding why.”
Atmospheric rivers carry large amounts of water vapor in narrow, ribbon-like storm systems that may stretch for a thousand miles and produce extreme rainfall and flooding once they make landfall. These storms repeatedly impact midlatitude coastal regions reminiscent of California, where atmospheric river events in January dropped huge amounts of rain, leading to catastrophic flooding.
Using satellite observations and climate model simulations, the scientists found that human-induced warming has increased the speed of atmospheric river storms within the Arctic. Additionally they found that one major mode of natural climate variability — the so-called Interdecadal Pacific Oscillation — also has contributed lately to atmospheric river changes. The results are particularly evident in the course of the winter ice-growing season within the Barents and Kara seas off the northern coasts of Norway and Russia.
“We frequently think that Arctic sea ice decline is a gradual process,” said study coauthor L. Ruby Leung of Pacific Northwest National Laboratory. “This study is essential in that it finds sea ice decline is because of episodic extreme weather events, [which] have occurred more incessantly in recent a long time partly because of global warming.”
Warm moisture carried by these storms increases what scientists call downward longwave radiation — heat emitted back to the earth from the atmosphere. It also produces rain. Either phenomenon can melt the skinny, fragile ice cover that normally regrows in the course of the winter months.
Using satellite distant sensing images, the scientists observed sea-ice retreat almost immediately following atmospheric-river storms, and saw the retreat continued for as much as 10 days.
“When this sort of moisture transport happens within the Arctic, the effect is just not only the quantity of rain or snow that falls from it, but additionally the powerful melting effect on the ice,” said Mingfang Ting, a professor on the Columbia Climate School’s Lamont-Doherty Earth Observatory and a coauthor of the study.
The lack of Arctic sea ice has broad implications. Open waters are darker than ice-covered ones and thus absorb more solar energy; this process feeds on itself, amplifying warming of the polar region. Ice-free waters may open up latest, more direct shipping routes, and access to minerals and other resources, but may trigger international geopolitical struggles. Moreover, freshwater melting into the salty ocean may impact oceanic circulations patterns. The rapid lack of sea ice is bringing erosion of Arctic coastlines, disturbance to global weather patterns and disruption of Arctic communities and ecosystems, said Ting.
“This study, along with other work that noted the presence of atmospheric rivers within the tropics, highlights that atmospheric rivers represent a worldwide phenomenon,” said Bin Guan of the California Institute of Technology, a coauthor of the study.
Also contributing to the research was Gang Chen, professor on the University of California, Los Angeles. The project received support from the U.S. National Science Foundation, NASA and the U.S. Department of Energy.
Adapted from a press release by Penn State University.
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