When the White House announced Wednesday that it would withdraw from dozens of international organizations, tucked in among them was the world’s leading authority on climate science — the Intergovernmental Panel on Climate Change.
The organization produces the most pivotal assessments about the impacts of rising temperatures, what’s causing them to climb upward, and the risks of failing to curb climate pollution. Governments use the highly detailed assessments to help shape their responses to global warming. In quitting the IPCC, as it’s known, President Donald Trump is signaling that those effects are unimportant, climate scientists say.
“This is a move that is symbolizing something that the administration has been trying to make clear in many ways over the last year,” said Robert Kopp, a climate scientist at Rutgers University and a lead author on the IPCC’s most recent assessment report.
The organization was among the world’s first scientific bodies to warn that human activities like driving and heating homes were causing temperatures to rise worldwide. That came in 1995 when, in the group’s second major report, it said for the first time that research pointed to a “discernible human influence” on the climate. It wasn’t until 2007, in its fourth report, that the IPCC said it was “unequivocal” that people were causing temperatures to rise.
All of those effects have been dismissed by Trump, who calls climate change a hoax.
In reality, America’s exit from the IPCC began almost a year ago. Last February, the Trump administration prevented a U.S. delegation, including federal scientist Katherine Calvin, from attending a meeting in China to discuss the substance and timing of the IPCC’s next assessment, which is due next year. The administration also stopped supporting the organization financially and hasn’t nominated authors for its reports. That marked a de facto withdrawal by the U.S. from the group, scientists say.
The IPCC said in response to Trump’s announcement on Wednesday that a formal withdrawal isn’t necessary. The group is composed of governments that are members of the United Nations or the World Meteorological Organization, and participation has always been “voluntary, free and open to all WMO and UN Member countries,” the organization noted in a statement released Thursday.
The U.S. had traditionally sent an official delegation from the State Department and other agencies to participate in the regular meetings. Those officials would also be involved in reviewing and approving the IPCC assessment’s summary for policymakers, an influential scientific document that’s written to help nonexperts grasp the causes and effects of climate change.
The IPCC has been “singularly successful in being able to get the trust of governments — all governments — and produce assessments of the science, which allowed the governments to negotiate with each other in the UNFCCC on the basis of the science,” said Michael Oppenheimer, a long-time IPCC author and geosciences professor at Princeton University’s School of Public and International Affairs.
The move to leave the IPCC was tucked into a sprawling White House memo that removed the U.S. from 66 international agreements, organizations and pacts, including the U.N. Framework Convention on Climate Change, a treaty ratified by the U.S. Senate in 1992. The UNFCCC acts as the foundation for international climate action, including the 2015 Paris Agreement, and is undergirded by the IPCC.
Leaving the IPCC cements what’s already happening under the Trump administration — the rejection of the effects of climate change on American society.
“Our economy needs good information to thrive, even inconvenient information about droughts, heat waves, and sea level rise,” said Rob Jackson, a senior fellow at the Woods Institute for the Environment at Stanford.
It’s unclear how the IPCC would make up the lost U.S. funding, but there’s precedent for other nations to fill in the gap. When the first Trump administration announced in 2017 that it would discontinue its financial support for the organization, other members vowed to increase their contributions. The U.S. gave around $1.8 million to the IPCC in 2024, more by far than the other 34 countries and organizations that contributed to the group. Germany, the second-largest donor, gave $383,000.
The IPCC releases a major assessment report every five to seven years, which typically includes scientific contributions from dozens of U.S. authors. Historically, the State Department has nominated scientists to serve on these working groups. But the Trump administration declined to participate in the nomination process in 2025, as the IPCC prepares its next major assessment.
Instead, a group of universities banded together to form the U.S. Academic Alliance for the IPCC, an organization with authority to nominate U.S. scientists for IPCC reports. The group nominated 282 people in 2025 for the upcoming assessment cycle, and 63 U.S. scientists were ultimately approved for authorship.
The State Department also typically pays for U.S. authors to attend meetings. With that off the table, the USAA-IPCC has raised its own funds in the past year to support their travel. Whether those efforts can replace direct U.S. participation for future reports and meetings remains to be seen.
That doesn’t mean the government’s absence won’t be felt.
U.S. authors typically include a large number of federal scientists from agencies like NOAA and NASA. But last year, “the number of federal scientists who put their names forward to be nominated dropped precipitously, because they just felt like they couldn’t play that role,” said Pamela McElwee, a scientist at Rutgers University and chair of USAA-IPCC’s steering committee.
It’s also unlikely that the U.S. will send its usual team of representatives to approve the final report texts once the next IPCC assessment is completed. Each assessment cycle culminates in a series of summaries specifically intended to inform policymakers, and they are “negotiated line by line” by delegations from all participating nations, alongside the scientific authors, at a special plenary session, according to McElwee.
“They’re really meant to not just provide the best available science but provide it in a way that policymakers understand it — that’s the point of these negotiated summaries,” McElwee said. “It’s not serving the U.S. interest to not have the U.S. delegation there.”
It’s also unlikely that the U.S. would make use of the IPCC’s reports under Trump.
The assessments have historically informed other U.S. reports on climate change, including the congressionally mandated National Climate Assessment, which is released by the federal government every few years. But the Trump administration has promoted misinformation on climate change over the past year, including through a climate report from the Department of Energy that’s been widely discredited by scientists since its July release.
Oppenheimer, of Princeton, called the Trump administration’s move to leave the IPCC “an attempt to pull the U.S. back into the dark ages.” The administration “doesn’t want to recognize what the scientific reality is, and it doesn’t want to do anything constructive to participate in reducing greenhouse gases,” he said.
The future of the National Climate Assessment is also murky. The Trump administration in April dismissed hundreds of scientists working on the next report. Since then, the administration has invited several climate contrarians to write the next installment.
“The fact that the U.S. is not, then, signing onto a broadly accepted assessment of the science is just an indication that it’s removing itself from the evidence base that all of the nations of the world agree to,” said Kopp, the Rutgers scientist.
But, he added, “they’re not gonna negotiate around climate anyway — so maybe it doesn’t matter much.”
