The puzzling link between western wildfires and Arctic sea ice – Eurasia Review


“Some say the world will end in fire,” wrote Robert Frost a century ago. The poet described a popular view of the end of the world before moving on to its apocalyptic opposite, writing, “some say in the mirror”.

But the relationship between fire and ice, in terms of Earth’s climate, is not quite as “either or” as Frost describes it. In the case of a study presented today at the AGU 2021 fall meeting in New Orleans, this relationship is more “give and take”.

The team of researchers behind the recent study describes a link between shrinking sea ice and worsening wildfires in the western United States. As the sea ice melts from July to October, the sunlight warms the surrounding area which is increasingly icy. This ultimately brings warmth and fire-friendly conditions to remote states like California, Washington, and Oregon later in the fall and early winter.

Researchers describe this relationship Рits existence was previously known, but its underlying mechanism now described for the first time Рas influential as climate models like El Ni̱o-Southern Oscillation.

“It’s not a perfect analogy, but teleconnects like this are a bit like the butterfly effect,” said Hailong Wang, a geologist at the Department of Energy’s Pacific Northwest National Laboratory and co-author of the new study. It refers to the popular feature of chaos theory where the flapping wings of a butterfly are believed to influence the formation of a distant tornado.

“Climatic conditions in one part of the world can, over time, influence climate outcomes for thousands of kilometers,” Wang said. “In our case, we see that the Arctic region and the western United States are linked by this relationship. Regional warming of land and sea surfaces caused by the loss of sea ice will trigger warmer and drier conditions in the west by far later in the year.

A story of two whirlpools

Wang and his fellow authors found that as the Arctic sea ice melts and the surrounding land and sea surfaces warm, a vortex builds up in the atmosphere above the heated area. This vortex, rotating counterclockwise like a cyclone, is generated by differences in atmospheric pressure.

The powerful vortex is constantly pushing the polar jet stream out of its typical pattern, diverting moist air from the western United States. As the now more undulating jet stream has moved away from its usual course, a second, clockwise spinning vortex forms below the crest of the polar jet over the western states. -United. This second vortex, similar to the vortex responsible for the extreme heat in the Pacific Northwest earlier this summer, brings clear skies, dry conditions and other weather conditions conducive to fires.

As the Arctic continues to warm, it can accentuate the contrast between these two connected distant systems, further exacerbating conditions in an area already ravaged by fires. More than three million acres burned across California in the 2021 wildfire season.

“This dynamics-based connection is heating up and drying up the western region of the United States,” said Yufei Zou, senior author and data scientist who was a post-doctoral fellow at PNNL when the study was conducted. “By discovering the mechanism behind this teleconnection, we hope that those responsible for forest management and forest fire preparedness will be better informed.”

Less ice, more heat

To probe the influence of the Arctic sea ice on the formation of climatic conditions favorable to fire, the authors of the study used the last four decades of recorded sea ice levels. The team isolated the mechanism at play through modeling conducted at the National Energy Research Scientific Computing Center, a user facility of the DOE Office of Science at the Lawrence Berkeley National Laboratory.

Arctic sea ice has been shrinking steadily since scientists began to measure its loss in the late 1970s. Late summer sea ice cover has declined 13% each decade from the previous decade. 1981-2010 average, according to the National Oceanic and Atmospheric Administration.

Arctic sea ice is expected to continue to decline, eventually leading to periods of ice-free arctic waters before the 2050s. Today, even the older and thicker ice that persists year-round is now thinner and larger. brittle.


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