Wells Griffith, Mr. Trump’s international energy and climate adviser, managed in one quote to summarize the dismissiveness of the American delegation and its fealty to the president’s apparently unshakable conviction that anything that helps the environment must inevitably hurt the economy. “The United States has an abundance of natural resources and is not going to keep them in the ground,” he said. “We strongly believe that no country should have to sacrifice their economic prosperity or energy security in pursuit of environmental sustainability.” The administration is full of zero-sum philosophers like Mr. Griffith. The idea that sustainability may be a necessary condition of future economic growth appears never to have crossed their minds.

Further depressing the proceedings were recent defections and political troubles in countries that, along with the United States, had been expected to lead the way to a low-carbon energy future. Germany, which long ago walked away from carbon-free nuclear power, is having a hard time cutting back on coal because of political opposition. In Australia, a prime minister was kicked out of office because he wanted to reduce the use of coal, which Australia produces in abundance. China, despite admirably aggressive investments in wind and solar power, has yet to get a firm grip on its emissions from coal-fired plants. The new president-elect of Brazil, Jair Bolsonaro, not only named an outspoken climate-change denier as his foreign minister but also, reversing his predecessors’ policy, pledged to open up the Amazon to mining and farming. This will threaten biodiversity in one of the world’s great rain forests while crippling its ability to act as a sink for carbon emissions.

No country’s backsliding, of course, compares with Mr. Trump’s. Determined to demolish President Barack Obama’s entire climate strategy, Mr. Trump has in the past year replaced Mr. Obama’s clean-power plan, which was aimed at reducing carbon dioxide emissions from power plants, with an essentially useless substitute that would emit 12 times the pollution envisaged by the Obama plan. He has proposed weakening a major Obama regulation requiring automakers to nearly double the fuel economy of passenger vehicles by 2025. (This rollback, The Times reported this month, came after a lot of whining by oil interests, not, as one might suspect, from the auto companies, which had accepted the challenge.) And the Environmental Protection Agency and the Interior Department have taken multiple steps to roll back Obama-era efforts to control emissions of methane, a greenhouse gas many times more powerful than carbon dioxide. These three programs formed the basis of Mr. Obama’s pledge at the 2015 Paris meeting to reduce America’s greenhouse gas emissions by 26 percent to 28 percent below 2005 levels by 2025.

The health and environmental effects of the Trump rollbacks, as documented by a Times investigation published this week, are far-reaching and potentially devastating.

This holiday season has brought more gifts to fossil fuel interests; every day is Christmas Day for the likes of Murray Energy and Exxon Mobil. This month , the E.P.A. proposed killing an Obama rule that would effectively block the construction of new coal-fired power plants. The Interior Department relaxed restrictions on oil and gas drilling in areas inhabited by the sage grouse, a threatened bird. Also in December , the department released an environmental-impact statement that would open all or part of the 1.5 million-acre coastal plain of the Arctic National Wildlife Refuge to leasing and exploration. The area had been off limits to drilling for decades until Congress, late last year, approved an amendment sponsored by Senator Lisa Murkowski, an Alaska Republican, to open it up.