This week is the third anniversary of the Paris climate agreement. The Trump administration marked it by working with Russia and Gulf oil nations to sideline science and undermine the accord at climate talks underway in Katowice, Poland.

While I was in New Delhi this week, where I met with solar energy advocates, a comment made thousands of miles away by the journalist Bob Woodward almost jumped off my iPad: The president, he said, “makes decisions often without a factual basis.” This isn’t a mere personality quirk of the leader of the free world. It is profoundly dangerous for the entire planet.

Scientists tell us we must act now to avoid the ravages of climate change. The collision of facts and alternative facts has hurt America’s efforts to confront this existential crisis. Ever since Mr. Trump announced that he would pull America out of the Paris accord, those of us in the fight have worked to demonstrate that the American people are still in.

But the test is not whether the nation’s cities and states can make up for Mr. Trump’s rejection of reality. They can. The test is whether the nations of the world will pull out of the mutual suicide pact that we’ve all passively joined through an inadequate response to this crisis.