Amid rumors that President Donald Trump will soon pull out of the Paris climate agreement that former President Barack Obama signed last year, more than 2,300 faculty from California universities have signed an open letter to the Trump administration calling for sustained action on climate change and urging the president to honor the country’s commitment to reducing greenhouse gas emissions as set forth in the agreement.

The United States signed the agreement last year, along with 193 other nations, and the provisions went into effect in November. Trump and some of his cabinet appointees, however, have expressed skepticism that human activities play a role in rising global temperatures, calling climate change a “hoax,” and argue that limits on greenhouse gas emissions, especially by coal-fired power plants, stifle the economy. After his inauguration, the White House removed any mention of climate change from its website, and climate scientists working at federal agencies are in fear of being muzzled or even fired.

“With some issues, we can hope to recover from a temporary backslide, but climate change is not one of those; we cannot afford to lose these next four years,” said Aaron Parsons, an associate professor of astronomy at UC Berkeley who first drafted the letter and asked his colleagues to sign it. “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 wrote and shared the letter shortly after Trump was sworn in as the 45th U.S. president, and found that it resonated among UC Berkeley faculty in all fields. He eventually sent it to colleagues outside the campus, and has gotten signatures from all UC campuses, as well as some California State University schools.

The challenge to Trump’s views on climate change has a champion in California Gov. Jerry Brown, who has come out swinging against Trump, threatening that the state will launch its own satellite if Trump shuts down climate monitoring satellites now operated by NASA.

“We want to give our politicians the ammunition they need, and let them know that they have our support,” Parsons said. “But we also want to empower scientists and intellectual leaders themselves to be more active on these issues. I hope we can build a voting base grounded in science and learning to oppose this anti-intellectualism we are seeing.”

The letter argues that the majority of scientists accept the fact that “continuing to produce greenhouse gases at current rates will have catastrophic, unstoppable consequences for our environment, our economy and our country. Bold and decisive action may still avoid the worst scenarios, allow for adaptation to the changes, mitigate the damage and bring new economic opportunities to our country. To this end, we ask that you ensure America’s place as the global leader on climate action.”

Former President Barack Obama announced the country’s commitment to the Paris Agreement in conjunction with China, another large greenhouse gas emitter, but Congress has yet to ratify the agreement. Enough other countries have ratified it to put it into effect, committing all signatories to limiting greenhouse gas emissions, primarily carbon dioxide, so as to achieve zero net emissions by the second half of the 21st century and limit global warming by an average of 2 degrees Celsius (3.6 degrees Fahrenheit).

While members of the National Academy of Sciences and a large group of earth scientists have already sent Trump letters urging continued action on climate change, Parsons thought that a uniquely California voice encompassing all thought leaders, non-scientists as well as scientists, would send a strong message.

“On the one hand, it is easy to dismiss California as a liberal state, but on the other hand, it is the sixth- largest economy in the world and there’s a lot of good we can do as a state,” he said.

The letter concludes:”The United States now has a unique opportunity to lead the world in developing innovative ways to reduce greenhouse gas emissions. 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. For these reasons, we ask you to maintain and increase our country’s commitment to taking action on climate change, beginning with the current Paris Climate Agreement.”

Read the full text of the open letter to President Trump.