Climate change is making western wildfires much worse

New study finds higher temperatures and dryer land has allowed fires to spread across 16,000 more acres.

A firefighter covers his face while battling a wildfire near Morgan Hill, CA. CREDIT: AP/Noah Berger
A firefighter covers his face while battling a wildfire near Morgan Hill, CA. CREDIT: AP/Noah Berger

Human-caused climate change is driving wildfires to be far more destructive, new research found — nearly doubling the forest fire area in the western United States over the past three decades.

Since 1984, aridity stemming from higher temperatures has allowed wildfires to spread across 16,000 square miles more than they otherwise would have, according to the study, published Monday in the Proceedings of the National Academy of Sciences. That’s equivalent to an area larger than Massachusetts and Connecticut combined.

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“No matter how hard we try, the fires are going to keep getting bigger, and the reason is really clear,” Park Williams, coauthor and bioclimatologist at Columbia University’s Lamont-Doherty Earth Observatory, said in a statement. “Climate is really running the show in terms of what burns. We should be getting ready for bigger fire years than those familiar to previous generations.”

According to the study, temperatures in forested parts of the west increased about 2.5 degrees Fahrenheit since 1970, and are expected to keep rising. More heat dries out land as warmer air sucks up moisture that vegetation and soil would otherwise get. That drying effect is a major factor behind the rise in wildfires.

In the study, the west includes California, Oregon, Washington, Idaho, Utah, Nevada, Arizona, New Mexico, Montana, Colorado, and Wyoming.

Researchers noted that firefighting suppression techniques are also playing a role in facilitating more destructive fires. By constantly putting out fires, authorities have allowed areas saved to build up dry fuel that later ignites. “We’re seeing the consequence of very successful fire suppression, except now it’s not that successful anymore,” lead author John Abatzoglou, a geography professor at the University of Idaho, said in a statement.

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To reach their conclusions, researchers examined eight systems that rate forest aridity and compared them with actual fires, as well as climate models that estimate human-caused warming. The data showed that 55 percent of the increase in fuel aridity could be attributed to climate change. Researchers also concluded that global warming’s role in increasing aridity has grown since 2000, and will continue to do so.

The study comes less than a month after the Soberanes Fire near Big Sur, California became the most expensive wildfire in U.S. history. The blaze, which is 99 percent contained some two months after it started, has cost $236 million, the San Jose Mercury News reported. At its height, some 5,000 firefighters battled the fire that destroyed 57 homes and killed a bulldozer operator.

While the study is touted to be one of the first to quantify how much global warming is expanding wildfires in the west, for the past few years researchers have been warning that higher temperatures will almost certainly cause more wildfires worldwide.

Just last year, U.S Forest Service researchers and others published a study that found wildfire season has gotten longer and far more expensive, and the global area affected by wildfire has doubled in the last 35 years.

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And earlier this year, a study from the National Center for Atmospheric Research found an 80 percent probability that any summer between 2061 and 2080 will be warmer than the hottest on record across the world’s land areas unless greenhouse gas emissions are sharply curbed.