The West was engulfed in flames this year, as millions of acres burned across California, Montana, Oregon, and elsewhere, adding up to the most expensive fire season on record.
California alone battled blazes that covered more than a million acres, according to data from the California Department of Forestry and Fire Protection. The Thomas Fire near Santa Barbara ripped across 280,000 acres, making it the state’s largest wildfire ever. The wine country fires in Northern California were even more destructive, burning down nearly 9,000 structures and killing 44 people.
Climate change doesn’t “cause” wildfires, which can be ignited by campfires, lightning strikes, downed power lines, or arson. Other human actions, including decades of fire suppression, have also increased the risk and magnitude of these fires. But global warming does seem to be making the events worse.
Human-influenced climate change has doubled the area affected by forest fires during the last 30 years across the American West, scorching an additional 16,000 square miles, according to a 2016 study in Proceedings of the National Academy of Sciences.
Higher temperatures suck moisture out of soil, trees, and plants, turning forests into tinderboxes. In California, the added heat has been compounded by the prolonged drought from 2012 to 2016, which dried out vast swaths of wilderness and opened the door to a devastating beetle bark infestation. The twin forces have killed some 129 million trees across nearly nine million acres, building up a massive amount of fuel and significantly raising wildfire risks, according to the state fire department.
As both the highest-cost fire year and the highest-cost hurricane year, 2017 was very likely “the most expensive weather year ever,” according to a convincing case in the Atlantic.
“Both the wildfires and the unprecedented Atlantic hurricane season are similarly profound and troubling,” wrote Michael Mann, director of the Penn State Earth System Science Center, in an e-mail to MIT Technology Review. “I see them as twin climate change–exacerbated weather phenomena.”
The added danger of wildfires is that they can convert forests from sponges to sources of carbon dioxide, forming yet another climate feedback cycle. In fact, California’s forests emitted more carbon than they absorbed between 2001 and 2010, and two-thirds of the loss was attributable to wildfires, according to a 2015 study by researchers at the National Park Service and the University of California, Berkeley.
Tracing through this list, it becomes increasingly clear how the links between distant events lock into self-reinforcing loops: rising emissions, higher temperatures, shrinking sea ice, additional warming, extended droughts, bigger wildfires, and higher emissions still. That means it will become increasingly difficult to pull out of this spiral, making it increasingly urgent that we begin serious efforts to do so soon.