(Bloomberg) -- California’s biggest wildfire of the year has already burned more than 50,000 acres of timber and grass as NASA scientists say climate change is making such blazes more likely and harder to stop.

It’s a sobering scenario for the U.S. state with the highest wildfire risk, where land damaged or destroyed by fire has expanded fivefold over the last four decades. Almost a half-million homes worth an estimated $268 billion are threatened, according to Zillow. At 78 square miles, the area being torched is about a quarter the size of New York City.

“We’re living in a warming and a drier world, and with climate change we’re going to continue to see conditions that make fire s more likely,” Doug Morton, chief of the Biospheric Sciences Laboratory at NASA’s Goddard Space Center, said in a broadcast this week. “They’ll be definitely harder to suppress.”

The Walker fire, within the Plumas National Forest northeast of Sacramento, has been burning since Sept. 4 and became California’s biggest of the year on Friday. NASA satellites show plumes of smoke blowing east into Nevada and crossing Pyramid Lake. The National Interagency Fire Center expects above-normal conditions for large fires in California through October.

California leads the nation in wildfire risk, with more than a quarter of the state’s properties considered at high-to-extreme peril, according to the Insurance Information Institute, a New York-based industry group.

California’s fire season has expanded by 75 days across the Sierras and corresponds with an increase in the extent of forest fires across the state. Last year, California accounted for about a fifth of the 8.8 million acres burned nationally, according to the Fire Center. The U.S. spent more than $3.1 billion fighting fires last year.

“As climate conditions make vegetation and other fuels that are on the ground today more flammable, it’s likely we’ll see more fires, and the fires that do start will be more extreme,” Morton said from the center in suburban Washington.

Global warming also contributes to an increase in wildfires in regions such as the Amazon, the scientists said. In the first eight months of 2019, Brazil had almost 94,000 fires, the most since 2010. More than half have been in the Amazon, an including the massive fire the started in August and triggered a state of emergency in Brazil.

Swept-up smoke from those fires created “among the most unhealthy air quality conditions” anywhere in the last month in downwind areas of Brazil, Peru and Bolivia, Morton said.

Smoke Chemistry

In the U.S., NASA and the National Oceanographic and Atmospheric Administration this year are sending a fleet of science aircraft to analyze smoke chemistry far downwind from fires in the west and agricultural fires in the southeast.

NASA also studied Alaska’s 2015 fire season, in which a record 5.1 million acres burned. The researchers found an unusually high number of lightning strikes, generated by warmer temperatures that cause the atmosphere to create more convection — thunderstorms — which contributed to a larger burned area.

To contact the reporter on this story: Steve Geimann in Washington at sgeimann@bloomberg.net

To contact the editors responsible for this story: James Ludden at jludden@bloomberg.net, Tony Czuczka

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