Fires have been raging in California, Oregon and Washington for three weeks.
Fanned by winds amid record heat, the blazes have burnt millions of acres, destroyed thousands of homes, and killed at least 25 people.
California's Governor Gavin Newsom said the fires show the debate around climate change is "over".
"Just come to the state of California. Observe it with your own eyes," he told reporters from a charred mountainside.
