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WASHINGTON — Insurers are quietly reducing their exposure to fire-prone regions across the Western United States, putting new pressure on homeowners and raising concerns that climate change could eventually make insurance unaffordable in some areas.

Officials in California, Washington, Montana and Colorado are getting more complaints from people whose insurance companies have refused to renew their coverage. The complaints follow years of record-setting wildfires in both size and cost, a trend that scientists expect to continue as global warming accelerates.

“I think that we are not far away from a lot of weather-related events being too expensive for most people to purchase comprehensive coverage,” said Carolyn Kousky, executive director of the Wharton Risk Center at the University of Pennsylvania. “What happens then is the big question.”

On Tuesday, California’s Department of Insurance issued a report quantifying that pullback. For the ZIP codes most affected by the wildfires in 2015 and 2017, the number of homeowners dropped by their insurance companies jumped 10 percent between 2017 and 2018.