A woman walking past a gate outside the Capitol Building in Washington D.C. shields herself from the sun with a parasol

Extreme heat in cities such as Washington DC are a symptom of climate change.Credit: Tom Williams/CQ-Roll Call/Getty

US President Joe Biden’s administration has appointed a new director to lead the nation’s next major climate assessment, finalizing the roster of its federal climate team and marking the end of a turbulent period in the office that coordinates work on global warming.

By law, the US government must complete a national climate assessment every four years, reviewing the latest science and highlighting the local and regional impacts of climate change — with the goal of helping individuals, businesses and state and local officials to make decisions about how to curb emissions and adapt to global warming. The most recent such report was finalized in 2018.

Work on the next report — the fifth National Climate Assessment — began last year, under the administration of former US president Donald Trump, whose industry-friendly policies were often at odds with efforts to limit climate change. In November 2020, Trump officials appointed a climate-change denier to head the US Global Change Research Program (USGCRP), which produces the assessments and coordinates climate activities across 13 federal agencies. Many experts feared that the move was intended to influence the report.

Since Biden took office in January, his administration has been assembling its own team of specialists to work on it. The latest is Allison Crimmins, who has worked on climate issues for the past decade at the US Environmental Protection Agency (EPA) and was appointed this week to head the fifth assessment. She joins Mike Kuperberg, an environmental toxicologist at the US Department of Energy, who was restored as head of the USGCRP in May. Together, they will attempt to put the report back on track: it is a year behind schedule after delays in appointing authors and defining its scope.

“We want to put this out in a timely manner,” says Crimmins, who also worked on the fourth assessment. “But I think the most important part is ensuring the quality and the scientific integrity of this report.”

A turbulent period

Crimmins replaces Betsy Weatherhead, a veteran climate scientist at the University of Colorado Boulder, who was appointed by the Trump administration to lead the assessment. Controversially, Weatherhead was removed from the position and reassigned to the US Geological Survey in April — spurring accusations that the Biden White House is purging government scientists associated with the Trump administration, even if they are qualified. Nonetheless, for many scientists, the fact that a climate leadership team is in place and the fifth national climate assessment is finally under way comes as a welcome relief.

“We’re behind, and we need to get to work,” says Donald Wuebbles, a climate scientist at the University of Illinois at Urbana-Champaign who was a coordinating lead author on the 2018 assessment. With Kuperberg and Crimmins in charge, Wuebbles says, he is confident that the report is in good hands and will now move forward.

Climate researchers worried that the Trump administration would meddle with the assessment released in 2018, but it was published seemingly without any political interference. Those fears were revived last November, when David Legates, a climatologist on leave from the University of Delaware in Newark who has continually questioned mainstream climate science, was appointed executive director of the USGCRP.

However, his tenure lasted for only two months. A week before Trump left office in January, Kelvin Droegemeier, then-director of the White House Office of Science and Technology Policy (OSTP), dismissed Legates after media reports about an effort to undermine climate science. Legates and others had posted a series of papers online, purporting to debunk global warming — and the papers bore the seal of the White House as a stamp of approval, even though the authors had not received permission to use it.

A delayed report

Sources at the EPA and the USGCRP say Legates was unable to accomplish much during his brief time in the role. When the Biden administration took charge, it sought to speed up work on the fifth assessment, but one of its first actions — to remove Weatherhead — has been called into question. When asked about the decision to replace Weatherhead, an OSTP official focused on Crimmins, sharing a statement that she brings “extensive experience managing and convening voices across the Federal system and among a range of stakeholders”, which will be crucial to ensuring the success of the next assessment.

Wuebbles and other scientists say that Weatherhead had a solid vision for the climate assessment. But as a long-time academic, she had difficulty navigating interagency politics to bring people together and move the process forward, according to an EPA official who declined to be named because they were not authorized to speak on the matter. At the same time, the official said, the Trump administration set Weatherhead up for failure by appointing her too late in the process, neglecting to give her political support at the OSTP and then putting Legates in charge at the USGCRP. Both Weatherhead and Droegemeier declined to comment to Nature.

The outline of the fifth assessment has now been finalized and the leading co-authors appointed from various federal agencies. Crimmins says the final report, which is slated for release in 2023, will be more user-friendly than previous versions. Notably, it will also include climate models and projections that some Trump administration officials had tried to exclude because of their uncertainty.

“We’re not leaving anything off the table in terms of scenarios or models,” she says. “If it’s in the literature, we will be assessing it.”