Even in the winter when temperatures are below freezing and the ice should be recovering after the summer melt; the Arctic is losing sea ice quickly. A team of scientists lead by Penn State researchers discovered in a recent study that strong storms known as atmospheric rivers are increasingly making it to the Arctic throughout the winter, impeding sea ice recovery and being responsible for a third of all winter sea ice reduction.
“Arctic sea ice decline is among the most obvious evidence of global warming from the past several decades,” said Pengfei Zhang, assistant research professor of meteorology and atmospheric science at Penn State and lead author of the study. “Despite temperatures in the Arctic being well below freezing, sea ice decline in winter is still very significant. And our research shows atmospheric rivers are one factor in understanding why.”
Large amounts of water vapor are transported by atmospheric rivers, which are narrow, ribbon-like storm systems that can travel up to 1,000 miles before making landfall and dumping torrential rain and flooding. These storms regularly impact midlatitude coastal regions like California, where atmospheric river events in January, for example, dropped 11 inches of rain.
Scientists discovered that these storms are progressively reaching the Arctic, notably the Barents and Kara seas off the northern shores of Norway and Russia during the winter ice-growing season. This finding was made using satellite measurements and climate model simulations. They reported their findings Monday, Feb. 6, in the journal Nature Climate Change.
“We often think that Arctic sea ice decline is a gradual process due to gradual forcings like global warming,” said L. Ruby Leung, Battelle Fellow at Pacific Northwest National Laboratory, and a co-author. “This study is important in that it finds sea ice decline is due to episodic extreme weather events atmospheric rivers, which have occurred more frequently in recent decades partly due to global warming.”
These storms carry warm moisture that increases the amount of heat that is returned to Earth from the atmosphere as downward longwave radiation and creates rain, both of which have the potential to melt the thin, brittle ice cover that forms each winter.
Arctic sea ice decline is among the most obvious evidence of global warming from the past several decades. Despite temperatures in the Arctic being well below freezing, sea ice decline in winter is still very significant. And our research shows atmospheric rivers are one factor in understanding why.
Pengfei Zhang
The scientists discovered sea ice loss nearly immediately after atmospheric river storms and discovered the retreat lasted for up to 10 days using satellite remote sensing pictures. The scientists claimed that atmospheric rivers are impeding the seasonal sea-ice recovery in the Arctic due to this melting and the increase in storm frequency.
“When this kind of moisture transport happens in the Arctic, the effect is not only the amount of rain or snow that falls from it, but also the powerful melting effect on the ice,” said Mingfang Ting, a professor at Lamont-Doherty Earth Observatory, Columbia University, and a co-author.
“This is important since we are losing Arctic sea ice fast in the past few decades brought many unwanted consequences such as Arctic warming, erosion of Arctic coastlines, disturbance to global weather patterns, and disruption to the Arctic communities and ecosystems.”
The loss of Arctic sea ice has broad implications, the scientists said. New, more direct shipping routes could be made possible by open waterways, but this could also lead to geopolitical tensions between nations. Moreover, freshwater melting into the salty ocean may impact the patterns of marine circulation that maintain global temperatures.
“Those factors make this study especially important from a science perspective, but also from social and security perspectives,” said Laifang Li, assistant professor of meteorology and atmospheric science at Penn State and a co-author. “Sea ice melting has a big impact for the climate system and for society, and our study finds the Arctic is an open system and that climate change is way more complicated than temperature change alone can explain.”
The authors found that human-induced warming has increased the frequency of atmospheric river storms in the Arctic using large-ensemble climate models. But they also found that one major mode of natural climate variabilities the so-called Interdecadal Pacific Oscillation also contribute to atmospheric river changes.
“This study, together with other work that noted the presence of atmospheric rivers in the tropics, highlights that atmospheric rivers represent a global phenomenon,” said Bin Guan, Earth systems scientist at the University of California, Los Angeles and Jet Propulsion Laboratory, California Institute of Technology.
“Since they were discovered relatively recently in the 1990s, and even more recently in terms of recognizing their societal impacts atmospheric rivers provide an opportunity for potentially coordinated research and applications globally, that is, with today’s computational and technological capabilities.”
Also contributing to this research was Gang Chen, professor at the University of California, Los Angeles. Researchers involved on this project received support from the National Science Foundation, NASA, and the Department of Energy.
