Why are summertime forest fires so much more likely? Because climate change has already redefined the seasons in Northern California. Since the early 1970s, summers in Northern California have warmed by about 2.5 degrees Fahrenheit (1.8 degrees Celsius) on average. A few degrees may not sound like much, but heat has an exponential relationship with forest fire.
“Each degree of warming causes way more fire than the previous degree of warming did. And that’s a really big deal,” Park Williams, a climate scientist at Columbia University and an author of the paper, told me. Every additional increment in heat in the environment speeds up evaporation, dries out soil, and parches trees and vegetation, turning them into ready fuel for a blaze. For that reason, Williams said, hot summers essentially overpower anything else happening in Northern California. Even during a wet year, an intense heat wave can choke forests so that it is as though the rain never fell.