Atmospheric rivers aren’t just a problem for California. They also change the Arctic

CNN
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The Arctic is experiencing a rapid decrease in sea ice, even during the cold winter months, when it is expected to recover from the summer melt. Scientists say an often overlooked factor plays a more important role than previously thought: atmospheric rivers.

These long, narrow bands of moisture in the atmosphere carry warm air and water vapor from the tropics. They can stretch for thousands of miles and dump rain and snow when they make landfall.

In January, atmospheric rivers brought a parade of killer storms that triggered heavy rains, flooding and landslides in California.

Now they are increasingly reaching the Arctic, according to a study by a team led by scientists from Penn State University and published Monday in the journal Nature Climate Change.

Using satellite observations and climate models, scientists have found that atmospheric rivers reach the Arctic more frequently during the winter season, especially over the Barents-Kara Seas off the northern coast of Norway. and Russia.

The authors used satellite images to analyze the sea ice immediately after the atmospheric river storms and found that the sea ice retreated for up to 10 days.

In winter, temperatures in the Arctic are below freezing and the ice is expected to recover. Instead, these powerful storms slow seasonal ice recovery. Storms may be responsible for a third of Arctic winter sea ice loss, scientists have reported.

“The decline in Arctic sea ice is one of the clearest evidences of global warming in recent decades,” said Pengfei Zhang, lead author of the study and assistant research professor of atmospheric sciences at Penn State University, in a statement. “Although temperatures in the Arctic are well below freezing, the decline in sea ice in winter is still very significant. And our research shows that atmospheric rivers are a factor in understanding why.

Atmospheric rivers are inherently warmer than the surrounding Arctic environment and can act as a blanket, trapping heat near the Earth’s surface and preventing it from escaping to space. Their heavy rainfall also has a melting effect, especially on the fragile ice that regrows.

According to scientists, climate change amplifies the intensity of atmospheric rivers because a warmer atmosphere is able to hold more moisture, leading to more precipitation when it hits land.

Using climate modelling, the study also found evidence that global warming is one of the factors in the increased rate of atmospheric riverine storms in the Arctic.

The Arctic, which is warming up to four times faster than the rest of the planet, has undergone dramatic changes in recent decades. Last year, during its annual Arctic health check, scientists from the National Oceanic and Atmospheric Administration found that it had become warmer, wetter and wetter, with a rapid decline in sea cover. snow and an unprecedented melt at the end of the season.

This latest atmospheric river report adds another layer of complexity to these findings.

Marty Ralph, director of the Center for Western Weather and Water Extremes at the Scripps Institution of Oceanography in San Diego, who was not involved in the research, said the study underscores the greater impact of atmospheric rivers.

“It is clear that the future of Arctic sea ice depends to a large extent on the strength and frequency of occurrence of [atmospheric rivers]”, Ralph told CNN.

The melting of the Arctic sea ice has important consequences for the rest of the planet. The lack of reflective ice opens up the dark waters below, causing the ocean to absorb more heat, fueling a cycle of melting and warming. The melting of fresh water in the ocean can also disrupt ocean circulation patterns, exacerbating global warming.

“The melting of sea ice has a significant impact on the climate system and on society, and our study reveals that the Arctic is an open system and that climate change is much more complicated than temperature change alone. can explain,” Laifang Li, study co-author and assistant professor of meteorology and atmospheric sciences at Penn State, said in a statement.