Warming temperatures are responsible for nearly half of particulate pollution and two-thirds of carbon emissions from western U.S. wildfires between 1997 and 2020, according to a study published in the Proceedings of the National Academy of Sciences. The findings underscore how a hotter, drier climate drives larger and more frequent fires across the region.
Wildfires across the American West are evolving into a massive source of air pollution and carbon emissions, driven overwhelmingly by rising temperatures. A modeling study published in the Proceedings of the National Academy of Sciences reveals that warming is directly responsible for 65 percent of carbon emissions and 49 percent of particulate pollution originating from western wildfires over a 23-year period ending in 2020.
The research illustrates how a hotter, drier climate fuels more intense droughts and creates conditions where fires burn up to four times as large and strike three times as often as they did prior to the turn of the century. During severe fire seasons, such as the summer of 2020, these blazes became the leading source of particulate pollution in the West. In California alone, fires that year produced more carbon emissions than every power plant in the state combined.
Where Warming Drives the Burn
The study demonstrated that climate-driven warming played a more significant role in remote forests and shrublands than in California wildlands near urban centers, where human ignitions have long played a primary role according to the research findings. Scientists analyzed regional smoke quantities and the varying effects of temperature increases across different landscapes to isolate the impact of climate change.
“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.”
Loretta Mickley, Harvard University, via Yale
Forests Giving Way to Grasslands and Shrublands
As fires sweep through the Southern Rocky Mountains and other western ranges, burned forests are increasingly failing to regenerate. A University of Colorado Boulder-led study examining 22 burned areas across 710 square miles—including sites from the 2002 Hayman Fire near Colorado Springs and the 1996 Buffalo Creek Fire southwest of Denver—found that lower-elevation forests like ponderosa pine and Douglas fir are losing the resilience needed to bounce back under warmer, drier conditions.
While about half of the study area currently remains suitable for post-fire recovery, statistical modeling projects a sharp decline in the coming decades. Under a moderate emissions scenario where greenhouse gases begin to decline after 2040, less than 18 percent 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 percent for Douglas fir and 3.5 percent 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.”
Tom Veblen, professor of geography at CU Boulder, via Colorado
The Growing Threat in the Wildland-Urban Interface
Beyond remote timberlands, fires are increasingly impacting areas where human development intersects with wildland vegetation. Research led by Volker Radeloff, a professor of forest and wildlife ecology at the University of Wisconsin–Madison, published in the journal Science, shows that the largest areas near humans burned by wildfires are grass and shrublands rather than forests.
These regions, known as the Wildland-Urban Interface or WUI, cover about 10 percent of land in the United States and house roughly one-third of the population. Because grass and shrublands are widespread, burn faster, and recover much more quickly than forests, they create a continuous cycle of available fuel. This rapid recovery cycle means areas can burn again more frequently, threatening communities that continually rebuild in high-risk zones.
Texas has surpassed California as the state with the largest increase in WUI houses as human development expands across the American sunbelt. Despite the recurring threat of high-speed grassland fires—such as those that destroyed over 500 homes in Superior, Colorado, in 2021—economic and personal ties keep residents anchored to these landscapes.
“It is usually much easier to stay in the same place to build a house. Getting houses rebuilt, businesses reestablished quickly, is important. So, to just pack up and go is really hard for a community to do and happens quite rarely.”
Volker Radeloff, professor of forest and wildlife ecology at University of Wisconsin–Madison, via WISC
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