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.

“One of the most preposterous hoaxes in the history of the planet,” scoffed Rush Limbaugh of Palm Beach. Gov. Rick Scott’s administration went so far as to bar some agencies from even using the term “climate change,” according to the Florida Center for Investigative Reporting (Scott denied this).

Myopic Floridians have plenty of company. President Trump dismissed climate change as a hoax “created by and for the Chinese.” Senator James Inhofe, a Republican of Oklahoma, “disproved” climate change by taking a snowball onto the Senate floor and noting that it was chilly outside; using similarly rigorous scientific methods, he wrote a book about climate change called “The Greatest Hoax.”

Alas, denying climate change doesn’t actually prevent it. North Carolina passed a law in 2012 prohibiting the use of climate science in certain state planning, yet that didn’t intimidate Hurricane Florence last month. And banning the words “climate change” isn’t helping Florida now.

Some folks will say this isn’t the moment for politics. But don’t we have a responsibility to mitigate the next disaster?

Consider that the three warmest years on record are the last three. And that the 10 years of greatest loss of sea ice are all in the last dozen years.

It’s true that we can’t definitively link the damage from any one hurricane (or drought or forest fire) to rising carbon emissions. But think of it as playing with loaded dice: A double six might have occurred anyway, but much less often.

“There is strong consensus among scientists who study hurricanes and climate that warming temperatures should make more intense hurricanes possible,” Kerry Emanuel, a hurricane expert at M.I.T., told me. He said that the probability of Hurricane Florence-magnitude rains in North Carolina has roughly tripled since the middle of the 20th century.

Flooding actually causes more hurricane deaths than wind, and climate change amplifies flooding in two ways. First, it raises the base sea level, on top of which a tidal surge occurs. Second, warmer air holds more moisture — about 10 percent more so far — and that means more rain.

Prof. Michael E. Mann of Penn State told me that Hurricane Michael should be a wake-up call. “As should have Katrina, Irene, Sandy, Harvey, Irma, Florence,” he added wryly. “In each of these storms we can see the impact of climate change: Warmer seas means more energy to intensify these storms, more wind damage, bigger storm surge and more coastal flooding.”

As recently as the early 2000s, there wasn’t much difference between the parties on climate policy, and Senator John McCain campaigned in 2008 as a leader in reducing carbon emissions. In 2009, Donald Trump joined other business executives in backing more action to address climate change.

Yet in the following years Al Gore helped make climate change a Democratic issue, and the Koch brothers helped make climate denial a litmus test of Republican authenticity. Tribalism took over, and climate skepticism became part of the Republican creed. So polls show that today climate denial is far greater in the United States, home to the greatest scientific research in the world, than in just about any other major country.

Trump says he will pull the United States out of the Paris climate accord, and he had nothing substantive to say about a new United Nations report, which has been called a “deafening, piercing smoke alarm” of catastrophic consequences ahead from climate change.

Republicans are correct that all this is uncertain. But in every other context, we try to prevent threats that are uncertain, and it’s irrational for Trump to be obsessed with, say, Iran, when he seems indifferent to the prospect that we are collectively cooking our entire planet.

There are legitimate debates about the best way to reduce carbon emissions, and reason for skepticism that we will succeed. Carbon taxes would have to be very substantial to have a large impact, geoengineering is uncertain, and there will be painful trade-offs ahead.

We also should curb the dysfunctional National Flood Insurance Program, which encourages people to live in low-lying areas. One Mississippi home flooded 34 times in 32 years, resulting in payouts totaling almost 10 times what the home was worth.

But we’re not even having these debates.

I worry that television coverage in the coming days will be dominated by heroes on boats rescuing widows on rooftops. Yes, that human drama is riveting — but it doesn’t address the larger problem.

The way to tackle lung cancer wasn’t to celebrate heroic doctors treating patients in the cancer ward, while ignoring cigarette smoking, but rather to reduce cigarette use.

WASHINGTON — The Environmental Protection Agency on Tuesday placed the head of its Office of Children’s Health Protection on administrative leave, an unusual move that appeared to reflect an effort to minimize the role of the office.

Dr. Ruth Etzel, a pediatrician and epidemiologist who has been a leader in children’s environmental health for 30 years, joined the E.P.A. in 2015 after having served as a senior officer for environmental health research at the World Health Organization. She was placed on administrative leave late Tuesday and asked to hand over her badge, keys and cellphone, according to an E.P.A. official familiar with the decision who was not authorized to discuss the move and who asked not to be identified.

The official said Dr. Etzel was not facing disciplinary action and would continue to receive pay and benefits. No explanation was offered to the staff on Tuesday.

An E.P.A. spokesman, John Konkus, declined to give a reason for the administrative leave.

Four people within the E.P.A. and a dozen or so who work closely with the agency said that Dr. Etzel’s dismissal was one of several recent developments that have slowed the work of her department, the Office of Children’s Health Protection. Created by President Bill Clinton in 1997, it advises the E.P.A. leadership on the specific health and environmental-protection needs of children, which often leads to tougher or more stringent regulatory standards than those that might be required for adults.

That is because children can be more vulnerable than adults to pollutants or chemicals because their bodies are still developing and because they eat, drink and breathe more, relative to their size. In addition, some of their behaviors, such as crawling or putting things in their mouths, potentially expose them to chemicals or other harmful substances.

As a result, the findings of the office often lead to a push for stronger regulations on industrial pollutants such mercury and pesticides, which are linked to nerve damage in children, and smog, which is linked to increased rates of childhood asthma.

“To take away the badge and access from a top career official and shove them out the door is very rare,” said Christine Todd Whitman, who headed the E.P.A. under President George W. Bush. “If they’re not saying why they dismissed her, it creates the impression that it’s about the policies she worked on.” She described the children’s health office at the E.P.A. as “critical to the health of the future.”

Public health experts said that, since the start of the Trump administration, they had seen a clash between the E.P.A.’s top leadership, appointed by a president who has pushed for weakening environmental rules, and the children’s health office. The E.P.A. has reduced the size of other offices with mandates that sometimes clash with Mr. Trump’s anti-regulatory agenda, such as the Office of Environmental Justice, which is charged in part with protecting poor and minority populations from the health effects of pollution.

Mr. Konkus said that no such agenda was in play with the reduction in size and leadership of those offices.

“These offices will continue to be a part of headquarters and regional organizations,” he said in a statement. “Children’s health is and has always been a top priority for the Trump Administration and the E.P.A. in particular is focused on reducing lead exposure in schools, providing funds for a cleaner school bus fleet, and cleaning up toxic sites so that children have safe environments to learn and play,” the statement said.

As the Trump administration has pushed to weaken or roll back regulations on various pollutants, senior officials within the E.P.A. children’s office say some of their work has been sidelined. The E.P.A. official who described Dr. Etzel’s departure cited a proposal outlining a strategy for reducing childhood lead exposure, which had been in development for more than a year with the involvement of 17 federal agencies. That proposal been stalled since early July, the official said.

The children’s health office has also repeatedly objected to a proposal by senior E.P.A. officials to weaken a set of chemical safety standards for children put in place under the Obama administration. The standard bars farm workers under the age of 18 from applying the most toxic pesticides to fruits and vegetables.

After pesticide manufacturers protested that standard, the E.P.A.’s office of chemical regulation, led by a former lobbyist for the chemical industry, Nancy Beck, sought to eliminate it. Dr. Etzel refused to concur with that plan, according to people familiar with the process.

“This office is always placed in the position of arguing for stricter standards, because their whole raison d’être is that you need stricter standards to protect children’s health. For that reason, the various polluting industries just hate this office,” said Dr. Philip J. Landrigan, a pediatrician and epidemiologist who directs the Global Observatory on Pollution and Health at Boston College. “I see the placing of her on administrative leave as the opening gambit on dismantling the entire office.”

The American Academy of Pediatrics called for Dr. Etzel’s reinstatement and for the office to continue its mission “unimpeded.” Slowing or interrupting the office’s work “sends a dangerous message that children’s needs are not valued,” said Mark Del Monte, interim executive vice president of the academy, in a statement.

Experts praised Dr. Etzel as a star in her field. “This seems like a sneaky way for the E.P.A. to get rid of this program and not be upfront about it,” said Dr. Mona Hanna-Attisha, the director of the pediatric residency program at Hurley Medical Center, a teaching hospital affiliated with Michigan State University. Her analysis of blood tests in Flint, Mich., a community that became caught up in a lead crisis affecting its drinking water, played a key role in showing that residents were being poisoned by the lead. Dr. Hanna-Atisha called Dr. Etzel “an international leader in children’s health.”

The office Dr. Etzel oversees is small, with a budget of about $2 million and 15 full-time employees in Washington and 10 regional children’s health coordinators, some of whom have other responsibilities in addition to children’s health. However, it operates from an influential position: It is technically housed in the office of the E.P.A.’s top administrator, currently Andrew Wheeler, a former coal lobbyist who has served as the agency’s acting administrator since July.

It is not the only E.P.A. office to have lost leadership or personnel under the Trump administration. Officials in the E.P.A. employees’ union say that while the Trump administration has not closed major offices, it has drained them of staff or leaders.

Over the past two years, the E.P.A.’s Office of Environmental Compliance and Enforcement, which oversees the enforcement of regulations, dropped from about 252 employees to about 182, according to records kept by officials in the E.P.A. employees’ union. “They’re finding these other ways to hamper the work,” said Nicole Cantello, who heads the E.P.A. employee union in the agency’s Chicago office.

Shortly after Mr. Trump took office, his budget director, Mick Mulvaney, proposed eliminating the EPA’s 24-year-old environmental justice office, which was created under the Clinton administration to coordinate the agency’s efforts to address disproportionately high pollution rates in communities of color. The reorganization, and a related to plan to reduce funding for other civil rights programs, was part of a coordinated effort within the administration to implement a checklist, created by the conservative Heritage Foundation, that would eliminate or weaken dozens of civil rights and consumer enforcement programs that had been strengthened during the Obama administration.