Climate Change Is Fueling Wildfires Nationwide, New Report Warns

A warmer world makes for a more combustible country. That is the conclusion in the most comprehensive assessment of the effects of climate change on the United States, released by the Trump administration just weeks after the deadliest and most destructive wildfire in California history.

The report says the continued release of greenhouse gases from cars, factories and other sources will make fires more frequent, including very large fires that burn more than 12,400 acres. And wildfire risk in the United States will not just be a Western problem.

“One of the big warnings there is about the potential for increased fire in the Southeast,” said Andrew Light, a contributor to the report and a senior fellow at the World Resources Institute.

Human-caused warming has increased the area burned by wildfire in the Western U.S., according to the report, “particularly by drying forests and making them more susceptible to burning.”

A recent study cited by the report estimated the total acres burned in Western forests under current climate conditions and in a model without human-caused warming. It found that half as much forest area would have burned between 1984 and 2015 in a world not warmed by climate change.

Climate change is not the only factor determining the size and destructiveness of a fire. Humans are increasingly intruding into wildland areas to build communities, increasing both the likelihood of fires and their devastation. Historical wildland management that focused on fire suppression has created some areas that are ripe for burning.

“Wildfire is an essential part of many forest ecosystems, but two major factors have produced the catastrophic fires we’re seeing in the Western U.S. — old policies and human-caused climate change,” said Patrick Gonzalez, a forest ecologist at the University of California, Berkeley and a contributor to the climate report.

There is evidence “that area burned is more closely related to climate,” Gonzalez said.

The report notes that warmer winters in the Northwest have reduced snowpack, the thick layers of snow that would form in the mountains over winter and melt through spring and summer. The decline in snowpack has decreased the amount of water available in summer, increasing wildfire risk.

Forest fires in the region “are expected to increase as temperatures increase and as summer droughts deepen,” the report says.

Warmer temperatures and drought are also expected to increase wildfires in the Southeast, which already experiences more billion-dollar disasters than any other region in the United States.

Extreme wildfires are not only a consequence of climate change, they also can contribute to the rise in carbon emissions. “Two-thirds of the carbon emitted by California ecosystems from 2001 to 2010 came from 6 percent of the land area that burned,” said Gonzalez, referring to his published research.

Gonzalez said the result was that California’s ecosystem, including its grasslands and forests, actually emitted more greenhouse gases than it took in, becoming a net contributor to the planet’s warming.

And increasingly, there is concern about what happens after a fire strikes. During the past 15 or 20 years, the number of forests rebounding after a wildfire has declined.

“There’s questions about what’s going to come back where that fire burned through,” said John Abatzoglou, an associate professor in the Department of Geography at the University of Idaho. “Is it not going to regenerate as a forest? Are we going to see more grassland and shrub lands?”