By my count, representatives from roughly 190 countries are currently gathered in Hangzhou, China, to advance the current cycle of scientific assessment of the Intergovernmental Panel on Climate Change (IPCC). However, one country is notably absent: the United States. Just as I boarded my flight to China to attend the IPCC meeting as an observer, news broke that the Trump administration’s “work stop” order would prevent any US federal scientists from participating in this crucial IPCC meeting.
This raises urgent questions: How does this decision impact international climate collaboration, and what can we expect moving forward? The US has historically played a critical role in the IPCC in three main ways: providing scientific expertise, participating in negotiations, and helping to fund the process. The current de facto withdrawal affects all three.
Absence of Federal Scientific Expertise
One of the most immediate and significant consequences of the US withdrawal is the absence of US federal scientists at the IPCC plenary. US scientists from federal agencies such as NASA and NOAA have long played an important role. In this cycle, they have a prominent role in Working Group III (WG3), which focuses on climate change mitigation—assessing methods for reducing heat-trapping emissions and removing them from the atmosphere.
The impact of this absence is particularly severe because NASA’s chief scientist, Kate Calvin, is currently the co-chair of WG3. Without her leadership, the group loses an essential voice in shaping climate mitigation strategies.
Additionally, each working group relies on a Technical Support Unit (TSU) to provide scientific, technical, and organizational assistance. The WG3 TSU is staffed almost entirely by US personnel (9 of 10 people), and its contributions are substantial: just last cycle, the WG3 report spanned over 2,000 pages. Compounding the challenge, the NOAA Assessment Technical Support Unit, which provides editorial, data visualization, IT, and production services, is also sidelined by the work stoppage and anticipated attempts to dismantle NOAA.
While this stoppage is technically temporary, if federal experts continue to be barred from participating, it would represent a major loss to the IPCC’s ability to produce rigorous and comprehensive reports.
No US Negotiators at the Table
IPCC plenary meetings are where representatives from participating countries review, discuss, and make key decisions to advance the IPCC’s work. During the meeting this week, countries are debating outlines for all the major IPCC reports. This is an important moment that sets the stage for work over the next few years. While country negotiators do not author the reports themselves, the IPCC’s influence stems in part from its consensus-based approach—ensuring that governments accept and commit the science and its conclusions. The absence of US negotiators means that the US has effectively removed itself from this process.
Why does this matter? Without US participation, other countries will shape the discussions without US input, reducing the nation’s influence in shaping global climate assessments. This might be an overall benefit to the IPCC based on Trump’s public anti-science rhetoric on climate change, but historically the US has been a value-add to the process.
Loss of US Funding for the IPCC
Countries make voluntary contributions to support the IPCC’s work. The Biden administration had pledged approximately $1.5 million for this year’s IPCC budget, but those funds have not been delivered. Given Trump’s past actions—he pulled US funding from the IPCC during his previous term—there is little expectation that his administration will reinstate financial support.
The loss of US funding, while not crippling, creates additional financial strain for the IPCC. Other nations or philanthropists (Bloomberg stepped in to cover UNFCCC funding) may step in to fill the gap, but the de facto withdrawal reinforces the message that the US is abdicating from its commitments to international climate cooperation.
What This Means for the Future of the IPCC
Climate change is a global challenge that requires global solutions. The IPCC was founded to foster international collaboration on climate science—science that is not policy-prescriptive, but rather provides world leaders with information crucial to crafting policy decisions. While this week’s IPCC plenary is proceeding, the absence of the United States signals a retreat from international climate leadership at a time when the worsening climate crisis demands stronger global cooperation.
In the face of these restrictions, it’s important to remember that the IPCC’s structure allows for continued participation from non-federal scientists in the US—scientists like me. The IPCC’s strength lies in its ability to convene voluntary experts from universities, NGOs, research institutions, and government agencies worldwide. The last cycle included thousands of authors, most of whom are independent researchers unaffected by the federal work stoppage.
However, the withdrawal of US federal support weakens the IPCC’s collective ability to provide the science the world needs to help tackle the climate crisis. In a moment when urgent, coordinated action is needed, this step back from collaboration could have long-term consequences. The path forward may not be easy, but the IPCC will continue its work and adapt to these challenges. As an observer organization, the Union of Concerned Scientists will continue to actively engage in this important scientific process. The real question now is how long the US will remain on the sidelines, and at what cost to the global effort and US communities?