Carlo Allegri / Reuters Republican presidential nominee Donald Trump has claimed global warming is a hoax “created by and for the Chinese” and vowed to pull the United States out of the historic Paris climate agreement.

Hundreds of the world’s leading scientists, including famed physicist Stephen Hawking, warn in an open letter Tuesday that a Donald Trump win in November would prove disastrous to global efforts against climate change.

The Republican presidential nominee, who once claimed global warming is a hoax “/twitter.com/realDonaldTrump/status/265895292191248385?ref_src=twsrc%5Etfw"}}">created by and for the Chinese,” vowed in May that he would “cancel” the historic Paris climate agreement.

Opting out of that pact, write the 375 members of the U.S. National Academy of Sciences, including 30 Nobel Prize winners, would have “severe and long-lasting” consequences, both for the planet and for the United States’ credibility.

“A ‘Parexit,’” the letter states, “would send a clear signal to the rest of the world: ‘The United States does not care about the global problem of human-caused climate change. You are on your own.”

The U.S. and China ― the world’s two largest emitters of greenhouse gases ― officially ratified the Paris agreement earlier this month, a major step toward having the deal take effect this year. More than 170 nations signed the Paris agreement in April, committing to fight climate change by cutting carbon emissions.

“The United States can and must be a major player in developing innovative solutions to the problem of reducing emissions of greenhouse gases,” the letter says. “Nations that find innovative ways of decarbonizing energy systems and sequestering CO2 will be the economic leaders of the 21st century. Walking away from Paris makes it less likely that the U.S. will have a global leadership role, politically, economically, or morally. We cannot afford to cross that tipping point.”

Also among the signees is former Harvard biology professor E.O. Wilson, commonly known as the “father of biodiversity,” who earlier this month told The Huffington Post that his “main worry right now is that the Republican candidate might win the election.”

Rick Friedman via Getty Images Harvard University Professor E.O. Wilson in his office in Cambridge, Massachusetts.

Trump has made his feelings about climate change and environmental protection alarmingly clear. He’s said weather “goes up and it goes down,” and warned that unlike him, Democratic nominee Hillary Clinton wants to “shut down the mines.” Trump’s senior economic adviser, Stephen Moore, said that lifting all restrictions on mining, fracking and drilling is among the ways the GOP candidate plans to pay for his costly proposals.

Although Tuesday’s letter doesn’t mention Trump by name, it is a clear attempt to steer Americans away from casting votes in his favor come November.

“Human-caused climate change is not a belief, a hoax, or a conspiracy. It is a physical reality,” the scientists write. “During the Presidential primary campaign, claims were made that the Earth is not warming, or that warming is due to purely natural causes outside of human control. Such claims are inconsistent with reality.”

Famed astrophysicist Neil deGrasse Tyson didn’t sign the letter, but endorsed it in a statement Tuesday to Mashable.

“For lawmakers to not heed the advice of esteemed scientists on matters of science, in this the 21st century, signals the beginning of the end of an informed democracy,” Tyson told the publication.

View the full letter here.

Editor’s note: Donald Trump regularly incites political violence and is a serial liar, rampant xenophobe, racist, misogynist and birther who has repeatedly pledged to ban all Muslims — 1.6 billion members of an entire religion — from entering the U.S.