If it seems like wildfire plumes are growing larger in the West, University of Utah researchers say it's because they are.
And that poses a problem for air quality throughout North America.
University of Utah scientists found that the maximum height of smoke plumes rose on average by 100 meters, or nearly 330 feet, in and around Utah's mountain ranges and other mountainous regions across the West every year over a span of 17 years, ending in 2020. However, it's much worse in the Sierra Nevada range at the California-Nevada border, where plumes grew by 230 meters, or over 750 feet, every year during the same timeframe.
The results are based on an analysis of 4.6 million different wildfire plumes across the western U.S. and Canada from 2003 to 2020 during the months of August and September, which are typically at the peak of wildfire activity.
This trend is problematic because larger plumes can result in smoke being spread out farther, such as across the entire continent, said John Lin, a professor of atmospheric sciences at the University of Utah.
"When smoke is lofted to higher altitudes, it has the potential to be transported over longer distances, degrading air quality over a wider region," he said, in a university news release. "So wildfire smoke can go from a more localized issue to a regional to even continental problem."
The team's findings were published Wednesday in Scientific Reports.
These growing smoke heights are caused by a mixture of different variables, according to Kai Wilmot, a postdoctoral researcher in the Department of Atmospheric Sciences at the University of Utah. He said ongoing negative atmospheric trends such as aridity, declining snowpack and hotter temperatures are helping increase fire size and the heat released by the fire, all of which result in larger plumes.
While the study range covers 17 years of data, researchers said the largest jump in plume size occurred from 2017 to 2020, hitting California and Colorado especially hard. Wilmot said the results toward the end of the study range were "absolutely towering over the rest of the time series."
That's bad news for states like Utah, which are typically downwind of California fires.
"Should these trends persist into the future, it would suggest that enhanced Western U.S. wildfire activity will likely correspond to increasingly frequent degradation of air quality at local to continental scales," Wilmot said in a statement.
Some of this has already happened, too. For example, the study doesn't include 2021 data, which Wilmot said supports this trend. The smoke from fires in California and Oregon was thick enough in August 2021 that Salt Lake City’s air quality was among the worst in the world despite being hundreds of miles away from where the fires were burning.
Given these trends, the researchers say that it's important to prevent any human-caused fires, which Utah Gov. Spencer Cox and firefighters have called preventable. They add it's also important to reduce carbon emissions, which is considered the largest cause of the changing climate that is making fires larger — though they caution that likely won't make a difference in the near future.
"The reality is that some of these (climate change) impacts are already baked in, even if we cut emissions right now," Wilmot said. "It seems like largely we're along for the ride at the moment."