"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."
The above is the first paragraph from an open letter signed by 375 National Academy of Sciences scientists, including 60 Nobel Prize winners. The letter is meant to emphasize the urgency of taking measures now to address the consequences of man-made climate change.
The letter also calls out the ignorance of the Republican nominee for President of the United States, Donald Trump, for his stated plans to remove the USA from previous international agreements to address this worldwide issue.
The letter states, "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."
Trump has previously expressed his opinions on climate change, including a much ridiculed tweet from several years ago that it is a Chinese conspiracy. In fairness, he later claimed that this tweet was a joke, however, he has on numerous other occasions publicly stated that he does not believe in man-made climate change.
You can view the entire letter at this link: Open Letter on Climate Change