Stephen Hawking and 374 other scientists say don’t vote for Trump.

Scientists are warning Americans that Donald Trump, the Republican nominee for president, is unfit to serve because of his controversial and profoundly mistaken position on climate change.

375 of the world’s leading scientists published an open letter on Tuesday warning Americans about the dangers that a Donald Trump presidency presents to the environment.

The letter, published on ResponsibleScientists.org on Tuesday, and signed by 375 members of the National Academy of Scientists, opens by declaring:

Human-caused climate change is not a belief, a hoax, or a conspiracy. It is a physical reality.

The letter goes on to explain that human health, food production and even national security are at stake, and describes the matter as “basic science.”

The letter sharply criticizes Trump’s position on a matter of “basic science” by citing the threat of climate change and blasting his push for the US to leave the Paris Accord, noting:

It is of great concern that the Republican nominee for President has advocated U.S. withdrawal from the Paris Accord.

The following is an extensive excerpt from that letter:

Human-caused climate change is not a belief, a hoax, or a conspiracy. It is a physical reality. Fossil fuels powered the Industrial Revolution. But the burning of oil, coal, and gas also caused most of the historical increase in atmospheric levels of heat-trapping greenhouse gases. This increase in greenhouse gases is changing Earth’s climate. Our fingerprints on the climate system are visible everywhere. They are seen in warming of the oceans, the land surface, and the lower atmosphere. They are identifiable in sea level rise, altered rainfall patterns, retreat of Arctic sea ice, ocean acidification, and many other aspects of the climate system. Human-caused climate change is not something far removed from our day-to-day experience, affecting only the remote Arctic. It is present here and now, in our own country, in our own states, and in our own communities. 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. The basic science of how greenhouse gases trap heat is clear, and has been for over a century. … Thus it is of great concern that the Republican nominee for President has advocated U.S. withdrawal from the Paris Accord. A “Parexit” 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.” Such a decision would make it far more difficult to develop effective global strategies for mitigating and adapting to climate change. The consequences of opting out of the global community would be severe and long-lasting – for our planet’s climate and for the international credibility of the United States. The United States can and must be a major player in developing innovative solutions to the problem of reducing emissions of greenhouse gases. 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.

Time reports the Paris Accord was reached by 195 countries last year at the United Nations Climate Change Conference.

Trump has said in the past that he would “cancel” the Paris Accord.

Bottom line: If you really needed another reason to vote against Trump, here it is: Science.