Warming temperatures drove nearly half of particulate pollution and two-thirds of western wildfire carbon emissions between 1997 and 2020, according to a modeling study published in the Proceedings of the National Academy of Sciences. The findings underscore how climate-driven weather shifts are intensifying blazes across the U.S. West.
Warming Drives Two-Thirds of Wildfire Emissions in the U.S. West
Climate change is actively reshaping wildfire activity across the western United States, turning blazes into monumental sources of atmospheric pollution. A new modeling study published in the Proceedings of the National Academy of Sciences reveals that warming temperatures were directly responsible for 65 percent of carbon emissions and 49 percent of particulate matter originating from western wildfires between 1997 and 2020.
The research illustrates how hotter, drier weather and deeper droughts give rise to larger and more frequent fires. Across parts of the U.S., fires have grown up to four times as large and strike three times as frequently compared to conditions before the turn of the century. During the summer of 2020, a particularly brutal fire season, wildfires emerged as the leading source of particulate pollution in the West. In California alone, fires that year generated more carbon emissions than every power plant in the state combined, according to reporting by Yale.
The modeling indicates that warming played a heavier role in remote forests and shrublands than in California wildlands closer to cities, where human ignitions have long played a prominent part. By examining smoke quantities across regions alongside the varying effects of local warming, scientists isolated the climate signal in wildfire emissions. Our hope is that this work will spur efforts to think more deeply about how we manage land and wildfires in the western U.S.
said lead author Loretta Mickley of Harvard University, as noted in published findings.
Grasslands and Shrublands Burn Faster and Threaten More Homes
While public attention often focuses on burning timberlands, research led by Volker Radeloff, a professor of forest and wildlife ecology at the University of Wisconsin–Madison, shows that the largest areas near human development actually burned by wildfires are grass and shrublands, published recently in the journal Science.
These environments sit within the Wildland Urban Interface, or WUI, areas where human development meets wildland vegetation. Although the WUI covers roughly 10% of land in the United States, it houses about one-third of the nation’s population. Grass and shrublands burn and travel faster than forests, allowing grassland fires to spread to a larger number of homes than a typical forest fire might. According to university accounts, high winds during 2021 fueled fires that raced across open grasslands and destroyed more than 500 homes in Superior, Colorado.
Population shifts are expanding these vulnerable zones. Texas is now the state with the largest increase in the number of WUI houses. California had that distinction for a long time,
Radeloff noted, highlighting shifting development patterns across the American sunbelt.
Southern Rocky Mountain Forests Struggle to Recover After Fires
Beyond immediate smoke and property risks, severe wildfires are altering the fundamental composition of western landscapes. A University of Colorado Boulder-led study projects that when forests burn across the Southern Rocky Mountains, many will fail to regrow as forests, converting instead into grasslands and shrublands, as detailed in university research.
The research team examined 22 burned areas covering 710 square miles from southern Wyoming through Colorado to northern New Mexico, focusing on ponderosa pine and Douglas fir forests. These species constitute about half of the region’s forested land and include sites scarred by major historical blazes such as the 2002 Hayman Fire near Colorado Springs and the 1996 Buffalo Creek Fire southwest of Denver. Using satellite imagery and tree rings, investigators found that lower-elevation forests proved far less resilient under warmer, drier conditions.
“We project that post-fire recovery will be less likely in the future, with large percentages of the Southern Rocky Mountains becoming unsuitable for two important tree species—ponderosa pine and Douglas fir.”
Kyle Rodman, lead author and former PhD student in the Department of Geography at CU Boulder, via CU Boulder Today
Under a moderate emissions scenario where greenhouse gas emissions begin declining after 2040, the team estimates that less than 18% of Douglas fir and ponderosa pine forests will likely recover if burned by 2051. Under a higher emissions scenario, that recovery rate drops to 6.3% for Douglas fir and 3.5% for pine forests. The big takeaway here is that we can expect to have an increase in fire continue for the foreseeable future, and, at the same time, we are going to see much of our land convert from forest to non-forest,
said Tom Veblen, professor of geography at CU Boulder, referencing long-term climate projections.
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