In an effort led by a prominent Bay Area climate scientist, 375 members of the prestigious National Academy of Sciences — including 30 Nobel Prize winners — have signed an “open letter” urging Republican presidential nominee Donald Trump and other GOP politicians not to advocate withdrawing from the landmark Paris agreement aimed at keeping the Earth from getting warmer.

“The United States has to be a leader in international efforts to reduce greenhouse gas emissions and solve this global problem,” Benjamin Santer, of Lawrence Livermore Laboratory, said in a Tuesday morning press briefing.

Although the letter is addressed to the public, not Trump, Santer said, “If you have expertise in climate science, it would be an epic failure to remain silent when that scientific understanding is dismissed as a hoax or conspiracy.”

Even as the evidence of global warming has become unmistakable, Trump and many Republicans in Congress have called for pulling out of the Paris accord signed by the U.S. and 196 other nations in April. Trump has often called climate change science a hoax.

“We all reacted with some shock to statements from the Republican platform that would have reversed decades of progress,” said Kerry Emanuel, a professor of atmospheric science at the Massachusetts Institute of Technology and another letter organizer. “We felt we had to say something.”

The letter warns that a withdrawal from the Paris agreement would diminish America’s international credibility, hobble its economic competitiveness in green-energy technologies and undermine the world’s ability to cope with climate change.

“If you know the road ahead is washed out, you don’t keep driving down it,” said Santer, who in 1998 was awarded a MacArthur Fellowship “genius grant” for his statistical analyses that first linked actions by humans to global warming. “We have a responsibility to point out that the science is credible. … This letter is an attempt to affirm the reality of human-caused warming — and the serious consequences of doing nothing.”

Democratic presidential candidate Hillary Clinton has promised to accelerate President Barack Obama’s efforts on climate change and says the U.S. could produce a third of the nation’s electricity from renewable energy sources by 2027.

Still, Clinton has not yet embraced the one policy that many see as the best way to stop global warming: a carbon tax. Her campaign faces the tough challenge of appealing to both younger voters — who supported Vermont Sen. Bernie Sanders for his opposition to the Keystone pipeline and Arctic drilling — and older, pro-oil voters in swing states like Ohio.

In his first major speech on energy policy last May, Trump called the climate change deal “bad for U.S. business” and said the pact allows “foreign bureaucrats control over how much energy we use.”

In August, a news release from the Trump campaign on economic policy vowed to rescind “all the job-destroying Obama executive actions, including the Climate Action Plan.”

In an interview with The Washington Post’s editorial board in March, Trump said that “perhaps there’s a minor effect” to the Earth’s climate from greenhouse gas emissions. “But,” he added, “I’m not a big believer in man-made climate change.”

Like many climate change deniers, Trump also fails to understand the difference between weather and climate: Weather is what the atmosphere does in the short term; climate is the long-term average of weather, shaped by global forces such as the accumulation of greenhouse gases. While visiting California on a December day in 2013, he tweeted: “I’m in Los Angeles and it’s freezing. Global warming is a total, and very expensive, hoax!”

The Trump campaign did not immediately respond to the letter.

The Paris pact was the result of years of negotiations under the United Nations’ Framework Convention on Climate Change. It’s unclear whether the next president could actually change the Paris accord, which will have legal force once it is ratified in January by 55 countries that contribute 55 percent of global emissions. If ratified, the U.S. would have to wait four years to withdraw from the deal.

“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,” said astrophysicist Neil deGrasse Tyson, director of New York City’s Hayden Planetarium, said in a prepared statement.

Other prominent scientists who signed the letter included renowned physicists Stephen Hawking and Steven Chu, a Nobel Laureate who is a former energy secretary in the Obama administration.

Stanford professor Lawrence H. Goulder, director of the Stanford Center for Environmental and Energy Policy Analysis, said “the letter correctly indicates the importance of our political leaders’ recognizing these scientific findings. Success in combating this global problem requires broad, international participation, and U.S. leadership is crucial to achieving such participation.”

The National Academy of Sciences, whose members are distinguished scholars in science and engineering, provides independent advice to the U.S. government on scientific and technological issues.

Santer’s findings in the 1990s unleashed a firestorm of criticism from contrarians such as physicist Frederick Seitz, a former president of the National Academy of Sciences. But Santer gained respect in the mainstream scientific community for his ability to coordinate group efforts to address this important issue.

“This is an issue that will define us,” he said. “How we respond to climate change will be the legacy of our generation.”