More frequent atmospheric rivers are hampering Arctic sea ice recovery

Sea ice near the village of Kotzebue, Alaska. (Courtesy of Lamont-Doherty Earth Observatory)

The Arctic is losing sea ice rapidly, even in winter when temperatures are below freezing and the ice should recover from summer melt. Now, a new study in the magazine natural climate change Powerful storm systems called atmospheric rivers were found to be partly responsible; they increasingly reach the Arctic in winter, slowing sea ice recovery and accounting for a third of the total winter sea ice loss, the study found.

“Arctic sea ice loss is one of the clearest evidences of global warming over the past few decades,” said lead author Pengfei Zhang from Penn State. “Despite temperatures well below freezing in the Arctic, the reduction in winter sea ice has been dramatic. Our study suggests that atmospheric rivers are a factor in understanding why.”

Atmospheric rivers carry large amounts of water vapor in narrow banded storm systems that can extend a thousand miles and produce extreme rainfall and flooding when they make landfall.These storms often affect mid-latitude coastal regions such as California Atmospheric River Events in January Heavy rains have resulted in catastrophic flooding.

Using satellite observations and climate model simulations, scientists have found that human-caused warming has increased the incidence of atmospheric river storms in the Arctic. They also found that a major mode of natural climate change—the so-called decadal Pacific Oscillation—has also contributed to atmospheric river changes in recent years. This effect is particularly pronounced during the winter freezing season in the Barents and Kara Seas off the northern coasts of Norway and Russia.

“We generally think of Arctic sea ice loss as a gradual process,” said study co-author L. Ruby Leung of Pacific Northwest National Laboratory. “This study is important because it finds that sea ice declines are due to sporadic extreme weather events, [which] It’s happened more frequently in recent decades, partly because of global warming. “

The warm moisture carried by these storms increases what scientists call downward longwave radiation — the heat that radiates from the atmosphere back to Earth. It also produces rainwater. Both phenomena would melt thin, fragile ice sheets that usually regrow in winter.

Using satellite remote-sensing imagery, the scientists observed sea ice recede almost immediately after the atmospheric-river storm and found that this retreat lasted for up to 10 days.

“When this moisture transport occurs in the Arctic, the impact is not just in terms of rainfall or snowfall, but in a strong melting effect on the ice,” said Mingfang TingProfessor of Columbia Climate Institute Lamont-Doherty Earth Observatory and co-authors of the study.

The loss of Arctic sea ice has wide-ranging implications. Open waters are darker than ice-covered waters and thus absorb more solar energy; this process is self-sufficient, exacerbating warming in polar regions. Freezing waters could open up new, more direct shipping routes and access to minerals and other resources, but could also spark international geopolitical struggles. In addition, the influx of freshwater into the Aral Sea may affect ocean circulation patterns. Ding said the rapid loss of sea ice is eroding Arctic coastlines, disrupting global weather patterns and damaging Arctic communities and ecosystems.

“This study, along with other work that has noted the presence of atmospheric rivers in the tropics, highlights that atmospheric rivers represent a global phenomenon,” said Caltech’s Bin Guan, a co-author of the study.

UCLA professor Gang Chen also contributed to the study. The project was supported by the National Science Foundation, NASA and the U.S. Department of Energy.

Adapted from a Penn State press release.