Still, the gathering at the Environmental Protection Agency on Tuesday was deeply dismaying — and not only because of Mr. Trump’s tired complaints about job-killing regulations. Or his false promises of more jobs for coal workers whose industry is in irreversible decline because of cheaper natural gas and the tripling in capacity since 2008 of cleaner energy sources like wind and solar.

It was dismaying also because it repudiated the rock-solid scientific consensus that without swift action the consequences of climate change — rising seas, more devastating droughts, widespread species extinction — are likely to get steadily worse. It was dismaying because it reaffirmed the administration’s support for older, dirtier energy sources when all the economic momentum and new investment lies with newer, cleaner forms of energy. It was dismaying because it flew in the face of widespread public support for environmental protection — including the pleas of the executives of hundreds of major American corporations who fear that without energy innovation their costs will rise and their competitive edge over foreign companies will be lost.

Perhaps most important, Mr. Trump’s ignorance has stripped America of its hard-won role as a global leader on climate issues. There was some relief that Mr. Trump did not use the occasion to withdraw the United States from the Paris agreement concluded in December 2015, when 195 nations came together for the first time in a collective effort to reduce greenhouse gases, in large part because of the tireless efforts of Mr. Obama and his secretary of state, John Kerry, to bring the Chinese and India along.

But the truth is that Mr. Trump has, for all practical purposes, repudiated Paris. The initiatives that he threatens to dismantle are the very ones that support Mr. Obama’s expansive pledge in Paris to reduce America’s greenhouse gas emissions by more than one quarter below 2005 levels by 2025. Without them, the United States will have neither the tools nor the credibility to lead the world on emissions reduction, and surely the leaders of China and India and the rest of the world are smart enough to see this.

This raises two very real dangers. Either other big countries also pull out of the agreement. Or they decide to seize the initiative on clean energy sources, which would be good for the climate but bad for American industry.