Scientists Link Increasing Wildfires to Decreasing Sea Ice in the Arctic

A new study explains how melting ice in the Arctic is causing increased wildfires in the western United States.

Windy Fire Burning In Central California Threatens Sequoia Trees
David McNew / Getty Images

The sunny warmth of Southern California is located more than 3,000 miles from the frigid cold of the Arctic Ocean. And yet, the two are inextricably linked, as if by an invisible string.

That’s the conclusion of a new study by researchers at the U.S. Department of Energy’s Pacific Northwest National Laboratory (PNNL) in Richland, Washington. Presented this month at the fall meeting of the American Geophysical Union (AGU), the study describes for the first time a known, but previously unexplained, the connection between climate patterns in the Arctic and those in the western United States. Specifically, it ties diminishing sea ice in the Arctic to worsening wildfires in the West.

“As sea ice melts from July to October, sunlight warms the increasingly iceless, surrounding area,” PNNL explained in a news release. “This ultimately brings heat and fire-favorable conditions to distant states like California, Washington, and Oregon later in autumn and early winter.”

What Is Sea Ice?

Unlike glaciers and ice sheets which form on land, sea ice—frozen ocean water—forms, grows, and melts in the ocean. Also unlike its sister ice forms, sea ice extent changes on a yearly basis, expanding in winter and declining somewhat every summer.

Scientists liken the connection between the Arctic and the West to climate patterns like the El Niño-Southern Oscillation.

“It’s not a perfect analogy, but teleconnections like this are a bit like the butterfly effect,” explains PNNL Earth scientist and study co-author Hailong Wang, referring to a popular feature of chaos theory wherein a butterfly’s flapping wings are thought to influence the formation of a distant tornado. “Climate conditions in one part of the world can, over time, influence climate outcomes from thousands of kilometers away. In our case, we find the Arctic region and the western United States are connected by this relationship. Regional land and sea surface warming caused by sea ice loss distantly triggers hotter and drier conditions in the West later in the year.”

According to Wang and his colleagues, what moves warm air south from the Arctic is an atmospheric vortex above warming land and sea surfaces. Created by a difference in air pressure, the vortex spins counterclockwise like a cyclone over the Arctic, thereby pushing the polar jet stream out of its typical pattern. That diverts moist air away from the western United States, which creates a second vortex spinning in the opposite direction over western states. That second vortex, which is similar to a vortex that created an extreme heat wave in the Pacific Northwest in summer 2021, creates “clear skies, dry conditions, and other fire-favorable weather,” researchers conclude.

In California alone, wildfires this year have burned over 2 million acres of forest. Future wildfire seasons could be even more dramatic if the Arctic continues warming, which it’s expected to do, according to PNNL. Arctic sea ice has been continually declining since at least the late 1970s, it reports, adding that end-of-summer sea ice cover has declined at a rate of 13% per decade. If that continues, even the oldest, thickest sea ice will melt, creating iceless periods in Arctic waters by the 2050s.

Further underscoring PNNL’s warnings is the federal government’s Arctic Report Card, the latest edition of which was published this month by the National Oceanic and Atmospheric Administration (NOAA). Compiled by 111 scientists from 12 nations, it notes a “warmer, less frozen, and more uncertain future” for the Arctic as a result of climate change—as evidenced by Arctic temperatures in autumn 2020, which NOAA says was the warmest Arctic autumn on record dating back to 1900.

“The Arctic Report Card continues to show how the impacts of human-caused climate change are propelling the Arctic region into a dramatically different state than it was in just a few decades ago,” NOAA Administrator Rick Spinrad said in a statement. “The trends are alarming and undeniable. We face a decisive moment. We must take action to confront the climate crisis.”

Rotten sea ice at over 80 degrees North off the north coast of Svalbard
Climate change is causing sea ice to retreat rapidly. The latest science predicts that the Arctic will be completely ice free in the summer around 2054. Ashley Cooper / Getty Images

Now that scientists understand the mechanisms that connect Arctic ice to western wildfires, researchers at PNNL hope the United States will have more visibility into wildfire risk and more capacity for wildfire preparation and mitigation.

“This dynamics-driven connection warms and dries out the western United States region,” says data scientist Yufei Zou, the study’s lead author, who was a postdoctoral research fellow at PNNL when the study was conducted. “By uncovering the mechanism behind that teleconnection, we hope those in charge of managing forests and preparing for wildfires will be more informed.”

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View Article Sources
  1. Zou, Yufei, et al. "Increasing Large Wildfires Over the Western United States Linked To Diminishing Sea Ice In the Arctic." Nature Communications, vol. 12, no. 1, 2021, doi:10.1038/s41467-021-26232-9

  2. "Incidents Overview." Cal Fire CA.Gov.

  3. "Arctic Report Card: Update for 2021." National Oceanic and Atmospheric Administration, 2021.