The Trump administration abruptly removed a top official charting the US government’s research on global warming, just as his agency began writing the next climate report card.

Mike Kuperberg, a Department of Energy employee who has for years led the US Global Change Research Program, was notified on Friday that his assignment atop the agency had ended, according to two people familiar with the move who asked for anonymity discussing a personnel matter.

An email sent to Kuperberg’s address at the research program drew an automatic reply saying that effective November 6, his detail has ended and he’s returned to the Energy Department. The shift, which was reported earlier by the Washington Post, threatens to cause tumult as the program Kuperberg headed lines up authors and the contours of the next National Climate Assessment, expected to be published in 2023.

Kuperberg is expected to be replaced by David Legates, a climate skeptic who was recently installed as a deputy assistant secretary of the National Oceanic and Atmospheric Administration, according to one of the people familiar with the matter. Legates didn’t respond to an email and voice mail seeking comment.

Legates, a professor of climatology at the University of Delaware, has worked closely with climate denial groups such as the Heartland Institute and argued earlier this year that “carbon dioxide is plant food and is not a pollutant.”

The upheaval also could foreshadow more turmoil during President Donald Trump’s final weeks in office. Last week, the administration demoted the chairman of the Federal Energy Regulatory Commission, Neil Chatterjee, after a vote allowing electric grid operators to implement state carbon pricing plans.

Representatives of the Energy Department didn’t respond to a request for comment, and a White House spokesman declined to comment.

Scientists warned Monday that Kuperberg’s departure alone could have a profound affect on the climate report. Deadlines to nominate assessment authors and develop the technical inputs that form the backbone of the report are just days away. And some decisions about the scope of the analysis made by the departing Trump administration could be difficult for President-elect Joe Biden to rapidly undo.

“Who is in that role is very critical,” said Brenda Ekwurzel, director of climate science for the Union of Concerned Scientists.

“Mike Kuperberg really understood the ins and outs of what needed to be done,” and the work is time sensitive, Ekwurzel said. “It makes it harder if you do not have someone at the helm making sure that we’re moving forward full speed ahead, as carefully as we can.”

The National Climate Assessment is a congressionally mandated compendium of research about the state of climate change. It is released every four years by scientists and other experts from across federal agencies. The last version, released in 2018 and mostly charted by the Obama administration, concluded that the effects of global warming are accelerating and will cause widespread disruption.

Trump rejected its conclusions, saying “I don’t believe it.”