President Trump made good on his promise this week to withdraw from the Paris Climate Agreement. This wasn’t a surprise. But it still baffles us. Try as we might, we cannot see how America’s interests are served by this decision.

Our climate emergency does not respect borders. California’s forest fires will not burn less fiercely, and rising sea levels will not spare Miami or Mar-a-Lago, just because Mr. Trump has chosen to opt out of a treaty of nearly 200 nations that represents our best and only chance of saving humanity from the catastrophic effects of rising temperatures.

Let us put it in language Mr. Trump might understand. If average global temperatures rise by the end of the century by another one degree Celsius, or 1.8 degrees Fahrenheit, there will be no winners on this planet. Only losers.

And those immigrants the president rails against? Expect the trickle to become a flood. Climate change could force 1.4 million people to abandon their homes in Mexico and Central America, according to the World Bank. That is because one-third of all jobs in the region remain linked to agriculture and climate change is making those livelihoods more precarious. The best way to keep climate refugees from the United States’ doorstep is to support a vigorous and effective climate agreement that helps protect America’s neighbors from the ravages of drought and erratic weather patterns. But Mr. Trump is turning his back on this opportunity.