Climate crisis

Scientists find a mind-bending link between sea ice loss and California wildfires

Model simulations suggest a link between sea ice loss and the increasing probability of large wildfires.

NASA

Since the late 1970s, Arctic sea ice has rapidly declined in the months of summer and autumn — all thanks to rising surface air temperatures close to two times higher than the global average.

Climate scientists project Arctic sea ice might dwindle away almost completely before the 2050s.

Meanwhile, at a far lower latitude in the western United States, annual wildfires have become a grim routine in California, Oregon, and Colorado. While the West Coast of the United States is around 1,455 miles away from the Arctic, new research suggests they are connected by thick waves of air circulation.

Climate scientists have hypothesized this dynamic and long-distance connection between the two radically different regions could be the reason why high-latitude climate change in the Arctic may affect lower latitude regions like the western U.S. — further exacerbating the climate crisis.

A schematic diagram illustrating the link between Arctic sea-ice loss and wildfires in the western United States. NASA/Goddard Space Flight Center Scientific Visualization Studio/Nature Communications

In a modeling study published in the journal Nature Communications on Wednesday, researchers describe a physical mechanism that demonstrates how receding Arctic sea ice could be linked to changes in downstream air circulation patterns.

This might eventually result in hotter and drier weather conditions in the western U.S., thereby increasing the frequency of large wildfires over the region.

“There are many other natural factors that could cause wildfires such as fuel aridity or the ignition of dry vegetation and dead trees,” co-author Hailong Wang, an earth systems analysis & modeling earth scientist at the Pacific Northwest National Laboratory, tells Inverse.

“But we now understand how the reduction in Arctic sea ice could affect local atmospheric conditions in low latitude regions where the majority of the population lives.”

The climate crisis, ice loss, and wildfires

Over the last few years, Wang and colleagues examined how changes in the Arctic, driven by climate change, influence the rest of the world. After studying how Arctic sea ice change could affect the air quality in East Asia, they decided to understand how it might trigger major wildfires in the western U.S. with the help of sophisticated climate modeling tools.

After compiling data from the last 40 years on Arctic sea ice concentrations, wildfire incidence, and weather conditions, the team conducted model simulations to analyze the interconnection between these factors. They observed that every year from July to October, massive Arctic sea-ice loss takes place.

Arctic sea ice in 1979 compared to 2020.EPA/NASA

As the ocean plays a role in heat storage and redistribution, the declining sea ice cover results in increased heat being released into the troposphere or lowest layer of the atmosphere over Arctic regions and even Alaska (that is located towards the northwestern direction of the Arctic ocean).

This further enables warm air to be transported from the ocean into the western U.S.

“This anomalous warm air could induce a low-pressure area over neighboring regions like Alaska,” Wang explains.

As the enhanced warm air flows from the ocean into the western U.S., it might exacerbate hot or dry conditions that could increase fire hazard risks.

“It’s not a direct impact,” Wang says. “The Arctic region and the western U.S. are connected by this wave structure or atmospheric circulation.”

Why this matters — Wang maintains that identifying this mechanism does not mean the western U.S. is far more vulnerable to major wildfires as compared to other regions in North America or Europe. Instead, the research spotlights the overall relationship between declining sea ice and susceptibility to wildfires overall.

These 2018 satellite images of the Camp Fire in California were captured by NASA. NASA

The study team hopes their findings can inform policymaking and better forest management.

“We can confidently say that the Arctic sea ice cover has been at its lowest during the last week of September in the past. This could be an indicator in the future that when the Arctic sea ice drastically depletes, wildfires’ risk could be high,” says Wang. “The good news is this can be observed a couple of months in advance.”

He hopes this new understanding can help local policymakers with forest management strategies that “might prevent wildfires from occurring in fire-prone areas in the first place.”

Abstract: The compound nature of large wildfires in combination with complex physical and biophysical processes affecting variations in hydroclimate and fuel conditions makes it difficult to directly connect wildfire changes over fire-prone regions like the western United States (U.S.) with anthropogenic climate change. Here we show that increasing large wildfires during autumn over the western U.S. are fueled by more fire-favorable weather associated with declines in Arctic sea ice during preceding months on both interannual and interdecadal time scales. Our analysis (based on observations, climate model sensitivity experiments, and a multi-model ensemble of climate simulations) demonstrates and explains the Arctic-driven teleconnection through regional circulation changes with the poleward-shifted polar jet stream and enhanced fire-favorable surface weather conditions. The fire weather changes driven by declining Arctic sea ice during the past four decades are of similar magnitude to other leading modes of climate variability such as the El Niño-Southern Oscillation that also influence fire weather in the western U.S.
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