California is burning, with at least 16 big wildfires statewide. The largest, in and around the northern city of Redding, has killed at least six people and burned more than a thousand homes and other structures.
Fires are nothing new in the state this time of year. It’s fire season, after all, as it is elsewhere in the West. But something feels different this time, perhaps because, following the Santa Rosa fire last October, this is the second year in a row in which fire has destroyed large parts of a city.
There are plenty of reasons for such destructive wildfires, including the fact that communities are encroaching more and more on forests, putting property and people at risk. But scientists say a climate change link is likely, too.
This summer’s record-high temperatures — the thermometer reached 111 Fahrenheit on the campus of the University of California, Los Angeles, in early July, for example — got most of the headlines. But from a fire perspective, individual records here and there are not as significant as extended periods of above-normal temperatures.
“What has been really unusual in the Western U.S. this summer has been the sustained heat,” said Alex Hall, a U.C.L.A. climate scientist. “It really pulls water out of vegetation, and that sets up conditions for big fires.”
“A month of somewhat elevated temperatures has a much bigger impact than just one day of really extreme heat,” he said. “It adds up.”
It’s not unusual for weather patterns to linger in summer, when the jet stream that would normally move big air masses around shifts to the north. But lingering weather that is 15 to 20 degrees above normal is something else. That was the situation in much of the state in July, including in Redding, where daytime temperatures did not drop below triple digits for 14 days straight.
Dr. Hall cautioned that no one had yet analyzed the sustained heat in California for the fingerprints of climate change. But he said he had no doubt that such a study would find that global warming made it more likely.
“The longer, the more sustained the signals are, the harder they are to explain through atmospheric circulation or the kinds of variability you associate with weather,” he said. Rather, he added, it suggests the climate is shifting. “It’s a new climate, if you will.”