Melting Arctic sea ice appears to be having far-reaching atmospheric impacts that increase the likelihood of extreme fall fire weather in the western United States, according to a study that used a mix of data analysis and computer modeling to draw this link.
The peer-reviewed research, funded by the federal Energy Department, was published in the journal Nature Communications and presented Thursday at the annual conference of the American Geophysical Union.
The authors say in summers with strong Arctic ice melt, the warmer sea temperatures result in more heat rising into the atmosphere. This creates a powerful vortex of winds circling counterclockwise, which can nudge the jet stream out of its typical pattern. This can bring drier air to the Western U.S., and prime fire conditions.
“Climate conditions in one part of the world can, over time, influence climate outcomes from thousands of kilometers away,” said Hailong Wang, an earth scientist at the Pacific Northwest National Laboratory in Richland, and one of four co-authors of the paper. “In our case, we find the Arctic region and the western United States are connected by this relationship. Regional land and sea ice warming caused by sea loss … triggers hotter and drier conditions in the West later in the year.”
The study covered a four-decade period when Arctic Sea ice has been in decline in a northern realm that has been warming more than twice as fast as the rest of the Earth.
The surface air temperatures over the Arctic for the 12-month period ending September 2021 ranked as the seventh warmest on record. This was the eighth consecutive year that temperatures were at least 1 degree Celsius (1.8 degrees Fahrenheit) above the long-term average, according to an “Arctic Report Card” released this month by the National Oceanic and Atmospheric Administration.
The study that Wang co-authored is part of a broader wave of research attempting to improve understanding of the impacts of the dramatic Arctic warming.
In a 2015 research article, Elizabeth Barnes of Colorado State University and James Screen of the University of Exeter wrote that it was still “an open question whether Arctic changes have an effect on the jet stream and thereby influence weather patterns farther south. This broad question has recently received a lot of scientific and media attention, but conclusions appear contradictory rather than consensual.”
That debate still continues.
Nick Bond, a University of Washington atmospheric scientist and the state’s climatologist, said the paper by Wang and his colleagues is based on solid research and “an interesting piece of work.” But Bond said the evidence they presented does not persuade him that there is a strong Arctic influence on Western fire weather. “I personally am not going to necessarily count on sea ice for expectations on what our fire reasons are going to be around here.”
Bond said that other climate models show a warming climate will be drying out the Northwest, and he hopes that this study will help spur additional research to investigate the relationships between the Arctic and the Western fire seasons.
Wang and his colleagues say the strongest correlations result from comparing Western fall fire seasons in six cool Arctic years that had the most summer sea ice with the six warmest years in the study period. This analysis, which covers California, Oregon and part of Washington, shows increases in the probability and intensity of fires.
The study suggests that, in the decades ahead, as the sea ice continues to retreat, the changing patterns of circulation will continue to escalate the late-season fire risks.
Wang said that it also is possible that melting Arctic sea ice could impact summer weather in the West, including events such as the heat dome that led to record June temperatures in British Columbia, Washington and Oregon. His research indicates that when the jet stream is pushed off course, a second vortex, spinning clockwise, can form that brings clear skies and dry condition similar to those during the summer heat wave.
But Wang said that it is too soon to draw any link, and that more research is needed in this area.