SAN FRANCISCO — Multiple mega fires burning more than three million acres. Millions of residents smothered in toxic air. Rolling blackouts and triple-digit heat waves. Climate change, in the words of one scientist, is smacking California in the face. The crisis facing the nation’s most populous state is more than just an accumulation of individual catastrophes. It is also an example of something climate experts have long worried about, but which few expected to see so soon: a cascade effect, in which a series of disasters overlap, triggering or amplifying each other. “You’re toppling dominoes in ways that Americans haven’t imagined,” said Roy Wright, who directed resilience programs for the Federal Emergency Management Agency until 2018 and grew up in Vacaville, Calif., near one of this year’s largest fires. “It’s apocalyptic.” The same could be said for the entire West Coast this week, to Washington and Oregon, where towns were decimated by infernos as firefighters were stretched to their limits./ NEW YORK TIMES