The world is heating up, and there are no “credible natural explanations for this amount of warming.” U.S. greenhouse-gas emissions have decreased a bit lately. But they need to go down much further and faster to avoid dire consequences.

Already, the nation is seeing “intensifying droughts, increasing heavy downpours, reducing snowpack,” as well as “declines in surface water quality.” Without a course change, increasingly depleted groundwater, rising seas and other effects will make it more difficult to farm and provide enough water for large cities.

Foodborne and waterborne diseases will spread. Disease-carrying ticks and mosquitoes will be more common. Extreme heat will cause more deaths. Wildfires and insect infestations will overwhelm U.S. forests. Sea ice will melt and coral reef ecosystems will dissolve. Power outages and fuel shortages will be more frequent. Roads and bridges will swamp. Pipelines will become unsafe. Waterside property will be increasingly unusable. Fisheries will dwindle.

“Even if significant emissions reductions occur, many of the effects from sea level rise over this century — and particularly through mid-century — are already locked in due to historical emissions,” the report explains, underscoring the necessity for coastal communities to prepare. On the horizon is “the potential need for millions of people and billions of dollars of coastal infrastructure to be relocated.”

Critics of acting on climate change often cite the possible economic costs. But not acting has costs, too. The experts expect “substantial net damage to the U.S. economy throughout this century,” finding that “with continued growth in emissions at historic rates, annual losses in some economic sectors are projected to reach hundreds of billions of dollars by the end of the century — more than the current gross domestic product (GDP) of many U.S. states.”

And the damage will be long-lasting. “The climate change resulting from human-caused emissions of carbon dioxide will persist for decades to millennia. Self-reinforcing cycles within the climate system have the potential to accelerate human-induced change and even shift Earth’s climate system into new states that are very different from those experienced in the recent past,” the report notes.

The White House responded to the report by misrepresenting scientists’ work and promising “fuller information” in the next analysis. Cooking the next report will not change the facts. Mr. Trump and the Republican Party have been negligent stewards of the country’s irreplaceable resources. Future Americans will not forgive or forget what these “leaders” did to them. Playing games with report release schedules won’t change that.

The president has made a habit out of pointing out America’s relatively clean air in interviews and in speeches. Just last week, Trump told the Associated Press, “I want the cleanest air on the planet and our air now is cleaner than it’s ever been.”

The United States indeed has far cleaner air than many other countries — especially developing ones with growing heavy-industry bases like India and China.

Even so, Trump’s Monday evening tweet is misleading in at least three different ways.

First, if the map shows a win for anyone, it’s former President Obama. The map Trump tweeted out came from an April report done by the World Health Organization, or WHO. But it shows air quality data worldwide for 2016. That is, of course, one year before Trump took office.

Obama, the president at that time, had pursued a plan to curb even more emissions of the sort of soot shown in the map from the nation’s power sector. That plan has been scrapped by the Trump administration for one that relaxes pollution limits on power plants despite an analysis from Trump’s own Environmental Protection Agency showing that Obama’s Clear Power Plan would have saved thousands of lives each year. Those particles are known to embed in the bloodstream and airways and are linked to deadly heart and lung diseases.

Even without that rule, concentrations of the tiny particulate matter have fallen through the United States since at least 2000. The cause is in part more economic than political: Many U.S. coal plants have shuttered as less carbon-intensive forms of electricity generation have grown, including natural gas, wind and solar power.

Second, the claim added to the map — that “none in [the] U.S.” are exposed to pollutions levels above WHO’s recommendations — is inaccurate.. While vast swaths of America have good air quality, there are pockets of pollution in the United States that are cause for concern.

In total, 45 U.S. cities, including Atlanta, Chicago, Houston and Los Angeles, have fine particulate concentrations above WHO’s recommended level, according to John Walke, a clean-air lawyer at the advocacy group Natural Resources Defense Council. That means tens of millions of Americans are exposed to that harmful fine particulate pollution — not none of them.

Finally, the United States does not have the world’s best air quality, as Trump claimed. According to WHO’s database of the annual average concentrations of fine particulate matter in urban areas, Australia, Brunei Darussalam, Canada, Estonia, Finland, Iceland, Sweden and New Zealand each were less polluted than the United States in 2016.

Still, by that metric the United States is ranked No. 9. That’s hardly an achievement to scoff at. The president is right to say the United States has clean air — it’s just not superlatively so.

But the bigger truth behind Trump’s tweet is perhaps how it highlights the diverging ways the two major political parties have reacted to the success of U.S. air pollution controls.

Republicans like Trump look at America’s relatively clean air and say there is no need for additional air regulations that would unduly burden businesses. In fact, a few of the existing rules could be safely rolled back, they argue.

Democrats look at the same data and say that success is because of the air-pollution rules put in place in the 1970s and built up by successive presidential administrations. They look at the clear air and see proof that the existing rules work.

The Republican approach is the one winning out at the moment. The EPA is rolling back not just rules meant to curb power-plant emissions, but ones designed to control smog-forming pollution from automobiles, too.