In Paris in 2015, the world’s nations pledged to do all they could to hold the rise of the planet’s temperature to 1.5 degrees Celsius (2.7 degrees Fahrenheit). It was a good idea since, though we’re still half a degree short of that number, we’re already seeing disastrous ice melt at the poles, the loss of coral reefs and the inexorable rise of the oceans. But at current rates of burning coal, gas and oil, we could put enough carbon in the atmosphere in the next four years to eventually push us past that temperature limit.

The planet’s hope, coming out of those Paris talks, was that we’d see such growth in renewable energy that we’d begin to close the gap between what physics demands and what our political systems have so far allowed in terms of action.

But everything Mr. Trump is doing should slow that momentum. He’s trying to give gas-guzzlers new life and slashing the money to help poor nations move toward clean energy; he and his advisers are even talking about pulling out of the Paris accords. He won’t be able to stop solar and wind power in their tracks, but his policies will slow the pace at which they would otherwise grow. Other presidents and other nations will have spewed more carbon into the atmosphere, but none will have insured, at such a critical moment, that carbon’s reign is extended.

The effects will be felt not immediately but over decades and centuries and millenniums. More ice will melt, and that will cut the planet’s reflectivity, amplifying the warming; more permafrost will thaw, and that will push more methane into the atmosphere, trapping yet more heat. The species that go extinct as a result of the warming won’t mostly die in the next four years, but they will die. The nations that will be submerged won’t sink beneath the waves on his watch, but they will sink. No president will be able to claw back this time — crucial time, since we’re right now breaking the back of the climate system.

We can hope other world leaders will pick up some of the slack. And we can protest. But even when we vote him out of office, Trumpism will persist, a dark stratum in the planet’s geological history. In some awful sense, his term could last forever.