CRESTLINE, Calif. — They appear at random, cinnamon-and-silver-colored pines and firs, the standing dead amid otherwise healthy groves of cloud-snagging trees in the mountains of Southern California. Last week, the Forest Service said there were 40 million of them — that is, 40 million dead trees in this state, almost one for every resident.

Soon, they will be fuel, for what rangers fear will be a catastrophic wildfire season — “40 million opportunities for fire,” as Agriculture Secretary Tom Vilsack put it. Or they will be ghosts, gone in that sweep when the earth broke all records for overheating.

The collapse of the conifers is blamed in large part on a beetle the size of a grain of rice that has metastasized with climate change. In record warm years — which is to say, nearly every year of the last decade — the trees’ natural defense systems weaken and beetles reproduce in large numbers. The infestation killing forests all over the Western Hemisphere has been called the largest insect outbreak in global history.

Anyone who wants to see climate change in all its accelerated misery can do what I did this week — take a walk in those dead woods. I went first to Cleveland National Forest, east of Anaheim, and then to San Bernardino National Forest, about a mile above the infinity of desert sprawl known as the Inland Empire. On one of the days, Donald Trump was holding a rally in the valley below.