Top Scientists Find Growing Evidence That Greenhouse Gases Are, in Fact, a Danger

The nation’s leading scientific advisory body issued a major report on Wednesday detailing the strongest evidence to date that carbon dioxide, methane and other planet-warming greenhouse gases are threatening human health.

The report, published by the National Academies of Sciences, Engineering, and Medicine, is significant because it could complicate the Trump administration’s efforts to revoke a landmark scientific determination, known as the endangerment finding, that underpins the federal government’s legal authority to control the pollution that is driving climate change.

The finding dates to 2009, when the Environmental Protection Agency concluded that planet-warming greenhouse gases pose a threat to public health and welfare and so should be regulated under the Clean Air Act. The Obama and Biden administrations used that determination to set strict limits on greenhouse gas emissions from cars, power plants and other industrial sources of pollution.

But in July, the Trump administration proposed to rescind the endangerment finding and contended that subsequent research had “cast significant doubt” on its accuracy.

The proposal is one of President Trump’s most significant steps yet to derail federal climate efforts. If the move is held up in court, future administrations would have no authority under the Clean Air Act to regulate greenhouse gas emissions from the burning of fossil fuels.

The new National Academies assessment contradicts the administration’s claims. The 136-page report, assembled by a committee of two dozen scientists, concludes that the original endangerment finding was accurate and “has stood the test of time.” It says that there is now even stronger evidence that rising greenhouse gas levels can threaten public health and well-being, and that new risks have been uncovered.

The report notes that multiple lines of evidence now show that human activities such as the burning of fossil fuels and deforestation are producing greenhouse gases that are heating the planet, and that climate change is exacerbating a wide variety of health risks like intense heat waves and increased wildfire smoke. Climate-driven changes in temperature and rainfall patterns have also led to negative effects on crops and less water availability in some places, among other disruptions.

The National Academies of Sciences, Engineering, and Medicine is a nongovernmental body that was originally chartered in 1863 by Abraham Lincoln to advise the nation on scientific and medical questions. The influential body issues roughly 200 reports per year on a range of topics from particle physics to neurobiology, and its members are elected each year.

In August, the National Academies announced that it was fast-tracking its study on the endangerment finding so that it could inform the E.P.A.’s decision-making process. Under federal law, the E.P.A. needs to solicit public comment on its proposal to revoke the finding and then must respond to all of the comments it receives.

Some Republicans in Congress criticized the National Academies for racing to complete the report. Representative James Comer of Kentucky, the leading Republican on the House Oversight Committee, wrote in a recent letter to the body that the decision was “a blatant partisan act to undermine the Trump Administration” and said that some of the members overseeing the report had “shown partisan bias.”

The committee that oversaw the report was led by Shirley Tilghman, an emeritus professor of molecular biology and public affairs and former president of Princeton University. While the committee was largely made up of academics, it also included a former employee of Chevron and a former executive at Cummins, a manufacturer of truck engines.

“This study was undertaken with the ultimate aim of informing the E.P.A., following its call for public comments, as it considers the status of the endangerment finding,” Dr. Tilghman said in a statement. “We are hopeful that the evidence summarized here shows the strong base of scientific evidence available to inform sound decision-making.”

In response to the report, Carolyn Holran, an E.P.A. spokeswoman, said, “The endangerment finding has been used by the Obama and Biden administrations to justify trillions of dollars of greenhouse gas regulations covering new motor vehicles and new motor vehicle engines. As we saw in the 16 intervening years since the endangerment finding was made, many of the extremely pessimistic predictions and assumptions E.P.A. relied upon have not materialized as expected.”

She said the E.P.A. “looks forward to responding to a diverse array of perspectives on this issue,” when the public comment period ends on Sept. 22.

To justify its proposal, the E.P.A. cited a variety of legal and technical arguments, saying among other things that the greenhouse gas emissions from vehicles on American roads are only a small sliver of total global greenhouse gas emissions.

But the agency also tried to argue with the mainstream scientific view that climate change poses a significant risk to humanity. It cited a report that the Energy Department commissioned by a working group of five prominent researchers who dissent from the mainstream scientific view of climate change. They were handpicked by Energy Secretary Chris Wright and while their report acknowledged that the Earth is warming, it said that climate change is “less damaging economically than commonly believed.”

In response, a team of more than 85 scientists wrote a 439-page reply, saying that the Energy Department analysis was riddled with errors and cherry-picked data to fit the president’s political agenda.

Separately, two environmental groups have filed a lawsuit in federal court charging that the formation of the Energy Department’s working group violated the Federal Advisory Committee Act and that the E.P.A. should not rely on its analysis. That case is ongoing.

Mr. Wright disbanded the working group this month in the wake of the lawsuit. But the Energy Department has said it has no plans to withdraw its report.

In a statement, Andrea Woods, an Energy Department spokeswoman, said that the agency had determined that the working group had achieved its purpose, “namely to catalyze broader discussion about the certainties and uncertainties of current climate science. We will continue to engage in the debate in favor of a more science-based and less ideological conversation around climate science.”

Some legal experts said that the Trump administration’s attempts to argue against longstanding scientific findings on climate change could create problems in court for its deregulatory efforts.

“It might have been a better strategy if they tried to sidestep the arguments about climate science altogether,” said Patrick Parenteau, an emeritus professor at the Vermont Law and Graduate School.

“Instead they’ve taken shots at climate science and that’s triggered an enormous response from scientists, and now they’re going to have to carefully respond to all of these comments,” Mr. Parenteau added. “And if they shortchange any of them, that creates a legal vulnerability. Courts are going to be very leery if the E.P.A. tries to ignore or reject the findings of the National Academies of Sciences.”