Warming temperatures are fueling increasingly larger and more frequent wildfires across the American West, creating a major source of air pollution. According to a Yale report detailing findings published in the Proceedings of the National Academy of Sciences, warming is directly responsible for nearly half of particulate pollution and two-thirds of carbon emissions unleashed by western fires.
Warming Climate Drives Larger and More Frequent Western Wildfires
Hotter, drier weather and intense droughts have caused fires in parts of the U.S. to grow up to four times as large and strike three times as often compared to before the turn of the century.
The modeling study revealed that warming played a greater role in remote forests and shrublands than in California wildlands near cities, where human ignition has a long history. Researchers determined that between 1997 and 2020, warming caused 65 percent of carbon emissions and 49 percent of particulates from western wildfires. 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.
Southern Rocky Mountain Forests Face Permanent Conversion
As fires continue to sweep across the region, a Colorado study indicates that many burned forests in the Southern Rocky Mountains will fail to grow back, converting instead into grasslands and shrublands. The research focused on ponderosa pine and Douglas fir forests, which comprise about half of the forested area in the region and are familiar to residents along Colorado’s Front Range.
The study analyzed historical burn sites, including land affected by the 1988 fires, the 1996 Buffalo Creek Fire southwest of Denver, the 2000 Eldorado Springs and Walker Ranch fires near Boulder, the 2002 Missionary Ridge fire outside of Durango, and the 2002 Hayman Fire—which burned more than 138,000 acres near Colorado Springs. Statistical modeling projected future outcomes across the next 80 years under varying greenhouse gas emissions scenarios.
Currently, researchers estimate that about half of the study area remains suitable for post-fire tree recovery to at least 1800s densities. However, under a moderate emissions scenario where emissions decline after 2040, less than 18 percent of Douglas fir and ponderosa pine forests are projected to recover if burned by 2051. Under a higher emissions scenario, recovery rates drop drastically to 6.3 percent for Douglas fir and 3.5 percent for pine forests. Kyle Rodman, the study’s lead author who conducted the research as a University of Colorado Boulder PhD student, created a post-fire recovery database to help land managers strategically invest resources after fires.
Grass and Shrubland Fires Drive Higher Human Risk in the WUI
While massive forest fires capture public attention, new research shows that the largest areas near humans burned by wildfires are actually grass and shrublands. According to a WISC report on a study published in the journal Science and led by University of Wisconsin–Madison professor Volker Radeloff, grassland and shrubland vegetation is far more widespread than forests.
Because grass and shrubland fires burn and move faster than forest fires, they can spread to a larger number of homes. High winds famously fueled fast-moving grassland fires that tore through homes in Superior, Colorado, in 2021, destroying over 500 homes. Population growth in regions like the American sunbelt is expanding the wildland-urban interface (WUI). Volker Radeloff noted that Texas currently holds the distinction of having the largest increase in WUI houses, a title previously held by California.
Census Bureau with U.S. Forest Service support, researchers mapped WUI areas and tracked home rebuilding. The findings show that wildfire risk in WUI vegetation does not deter people from rebuilding in previously burned areas. Grassland and shrubland vegetation recovers much more quickly than forests, supplying fresh fuel for fires to return to the same areas more frequently. Despite these recurring risks, communities rarely relocate, making home hardening and improved vegetation management essential tools for policymakers.
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