This was demonstrated just days after Mr. Trump’s announcement, when American governors, mayors, businesses, universities and others declared “We Are Still In,” pledging to meet the goals of the Paris agreement. The commitments of more than 2,500 such leaders are now formalized in the “America’s Pledge” effort, as they work to build upon those promises. It is an extraordinary, innovative move: citizens implementing a global agreement, a government obligation, standing as responsible actors of the global community.

Image Laurence Tubiana Credit... Stephane de Sakutin/Agence France-Presse — Getty Images

The private sector can see this is the future and companies are investing accordingly: The automotive industry is competing madly in the rush to switch to electric vehicles, while private investors are reluctant to invest in new coal power plants.

The battle over climate change at this year’s G-20 meeting starkly illustrated Mr. Trump’s growing isolation. Despite a failed attempt by the United States to rally a pro-fossil fuel coalition, including a pre-G-20 visit to Poland and an appeal to climate skeptics, often through social networks and the far-right press, trying to equate climate action as a clash between global elites and ordinary people, all 19 other countries reaffirmed their commitment to the Paris agreement, leaving the United States out in the cold.

Mr. Trump’s claim that this move will help the American economy does not hold up. In the fast-changing area of electric power generation alone, twice as many Americans work with solar technologies as in fossil fuels, and his slashing of federal research funding will hurt the country’s competitiveness.

We are also in a time when extreme events are becoming more frequent and more costly. Every year we have a once-in-500-years storm, and every year is the hottest on record. Hurricane Harvey, which made landfall on the mainland in southeast Texas, will be the costliest natural disaster in the history of the United States: Its estimated $190 billion price tag may exceed the combined costs of Hurricanes Katrina in 2005 and Sandy in 2012.