UNC system professors link wildfires in western U.S. to arctic warming

Wildfire activity in the western U.S. is linked to warming in the Arctic, according to a recent study. 

Researchers Peter Soulé and Paul Knapp are geography professors at Appalachian State University and UNC-Greensboro, respectively. They found evidence that Arctic sea-ice extent affects the upper-level jet stream above the U.S. — which in turn affects the atmosphere in places such as California. 

Knapp said years with low Arctic sea-ice extent correlate to a tendency of ridging in the western U.S. According to the researchers, ridging is when the upper-level jet stream bends northward and creates high atmospheric pressure. Below the ridge, or high atmospheric pressure, air sinks and leads to warmer, drier conditions. Such conditions are conducive to wildfire activity.

According to the study, the connection between Arctic sea-ice and the jet-stream in lower latitudes is an example of what climatologists call teleconnection, where what happens in one part of the world impacts the weather in other parts. 

“We’re in a very connected world, so changes in one spot can potentially have significant impacts in another area,” Knapp said. “I think if we continue to have reductions in Arctic sea-ice, we more than likely will have continued changes in the way the jet stream is behaving. It’s going to probably have a more meridional type of flow to it, which is going to create places that have unusually warm or unusually cool conditions because of that.”

Soulé said the teleconnection is affecting things such as wildfires, which are significant for ecosystem processors and humans. He cited the Californians who lost their lives to wildfires this year, as well as the economic costs of firefighting, as examples of its significance. 

“If humans are doing something to cause climate to change in such a way that it’s making it more conducive for this type of activity to occur, then that’s a pretty big thing,” he said.

Soulé said correlation does not mean causation, and atmospheric processes are very complex. 

According to Knapp, it's important not to attribute trends, such as increased wildfires, to one thing because it's probably a combination of factors that lead to changes. 

“Almost invariably when we have trends in something, it’s a combination of factors that have occurred,” Knapp said. “So for wildfire activity, I think this is one contributing factor, but there’s other things that have, in all likelihood, contributed to increased wildfire activity."

Jose Rial, a geophysics and climatology professor at UNC, said in an email one should not blame a single event on human-induced warming, although symptoms of global warming resulting from burning fossil fuels are everywhere. 

“The article by Soulé and Knapp points to one more of the mechanisms we are all concerned with,” Rial said. “The more we understand how the climate system functions, the better (our forecasts will be) and the better we can defend ourselves against a crisis that many deny but that will fall on all of us sooner or later.” 

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