With smoky skies becoming a ubiquitous feature of the American summer, a new study suggests wildfires may have “grown to a point where they can alter the climate state."
“These are transient effects that will have no bearing on the trajectory of climate — unless they happen all the time,” John Fasullo, a scientist at the National Center for Atmospheric Research, told The Hill of brush fires like the ones that ravaged Australia in 2019-2020.
Fasullo was the lead author on a new study that demonstrated the startling impact of Australian bush fires on the Earth’s climate last year — an impact they say surpassed the known climate effects of fewer emissions during pandemic-related lockdowns.
As the fires scorched the continent from late 2019 into 2020, plumes of smoke stretched into the stratosphere and circled much of the Southern Hemisphere — cooling the planet within six months by about 0.06 degrees Celsius, Fasullo and his colleagues observed, in a peer-reviewed study published Wednesday in Geophysical Research Letters.
The global cooling effect may have been temporary, but as such events become more frequent, researchers fear they may alter the course of climate systems long-term. Wildfires have ramifications on the entire climate system, causing bands of warmer weather elsewhere, as well as devastating land and lives locally. Science doesn't yet know what impact more frequent wildfires could have on climate change globally.
During the Australian brush fires, the Earth’s surface became significantly cooler, even as the fires released carbon dioxide into the atmosphere.
Fasullo likened this discrepancy to two distinct pools — the first being a slow-moving reservoir of carbon dioxide, which has an atmospheric lifetime of about 1,000 years. If a garden hose would release some carbon dioxide into that “huge bathtub,” he explained, no one is going to notice a difference anytime soon. But when aerosol emissions plummet as they did during the pandemic, Fasullo said, "it's like you've turned over the entire pool" — leaving an opening for gradual warming.
In the brush fire scenario, however, unusually high concentrations of aerosols made cloud droplets smaller and brighter, reflecting sunlight back to space. With less solar radiation available to absorb, the planet’s surface temporarily cooled down.
Such effects, Fasullo warned, were just a transient “cooling pulse” that resembled the aftermath of a volcanic eruption. But as wildfires become more frequent events, he explained, the repeated occurrence of such temporary pulses might make a lasting contribution to the larger climate system. While many studies exist on the impact of climate change on wildfire occurrence, there has been little research on the impact of wildfires on climate change, Fasullo said.
One reason that major fires might be so disruptive to the planet is that when they inject huge amounts of sulfates and other particles into the atmosphere, they push tropical thunderstorms northward from the equator and potentially influence the El Niño and La Niña warming and cooling cycles in the tropical Pacific Ocean, according to the study.
And the scientists are already seeing that these effects may have applied to both Australia and wildfires in the Pacific Northwest. Fasullo said he and his colleagues are researching whether 2017-2018 fires in British Columbia, Canada, played a role in triggering an El Niño in 2018-2019. Meanwhile, their simulations have suggested that the Australian brush fires did trigger a La Niña event that just recently ended.
El Niño events tend to occur only in the Northern Hemisphere, while La Niñas occur in the South, as the physics of these systems cause opposite reactions in each hemisphere, Fasullo explained.
The researchers said they used a computer modeling program to run more than 100 simulations that recreated global climates — both with and without emissions — under various atmospheric conditions from 2015 to 2024. They also evaluated the simulations in conjunction with real-world observations to better understand the impact emissions can have on the global climate.
Although it’s still too early to know whether the current Western wildfire season will be worth exploring, Fasullo said that “the way things are developing for Canada in particular, that may end up being a season that we want to look at.”
“Wildfires are an interactive component of the climate system, not just a slave of it,” he added. “They have the potential to alter the trajectory of year-to-year climate and also of the long-term climate.”
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