More than 2,300 faculty members from California public universities signed a letter to President Donald Trump urging him to take the threat of climate change seriously.

The letter, signed by faculty members from the University of California and California State University systems and released on Tuesday, asks Trump to maintain the U.S. commitment to reducing greenhouse gas emissions, as specified in the Paris climate change agreement President Barack Obama signed last year. Trump, who has characterized climate change as a hoax, has promised to pull out of that agreement.

“We ask that you ensure America’s place as the global leader on climate action,” reads the letter to Trump. “With this letter, we aim to express the degree to which the scientists and intellectual leaders of our state, speaking for themselves and not on behalf of their respective employers, agree on the facts of climate change. Despite misleading portrayals, there is widespread consensus in the scientific and academic communities that human-caused climate change is real, with consequences that are already being felt. The science of how greenhouse gases trap heat is unimpeachable.”

Trump’s early moves on climate policy have environmental advocates dismayed. His pick to lead the Environmental Protection Agency, Oklahoma Attorney General Scott Pruitt (R), won’t acknowledge that humans are contributing to climate change. Last week, the EPA froze grants programs and instructed employees to not talk to the press or use social media. Trump himself has proposed scrapping NASA’s climate research and holds views on climate change that are contrary to an overwhelming majority of climate scientists.

The open letter made that point loud and clear.

“The United States now has a unique opportunity to lead the world in developing innovative ways to reduce greenhouse gas emissions,” reads the letter. “By investing in and incentivizing clean energy and carbon sequestration technologies now, we position ourselves to be the economic and political leaders of the 21st century. To do otherwise cedes these opportunities to others and undermines our national security, food security, water security, and the future of our children and grandchildren.”

The letter was written by Aaron Parsons, an astronomy professor at U.C. Berkeley. Parsons told Berkeley News he began writing the letter shortly after the inauguration, noting that the adverse affects of global warming can’t be repaired with legislation by a future president after Trump leaves office.

“We are treading a thin line on whether it’s possible to avert major climate change, and it is absolutely imperative that we do everything we can,” Parsons said.

Parsons circulated the letter among his Berkeley colleagues, and then sent it to professors at other public colleges in the state. You can see who signed the letter here.

California Gov. Jerry Brown (D) also has spoken against Trump’s climate proposals, warning the president that California is “ready to fight.”

“If Trump turns off the satellites, California will launch its own damn satellite,” Brown said in December. “We’re going to collect that data.”

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