Although judges are not necessarily scientific experts, they are responsible for deciding whether scientific evidence is admissible and for making decisions in scientific cases. That’s why, Reference manual on scientific evidenceThe law, co-authored by the Federal Judiciary Center (FJC) and the National Academies of Sciences, Engineering, and Medicine (NASEM), was introduced more than 30 years ago to inform judges of fundamental truths in various fields of science.
“Lawyers and judges typically don’t have an extensive scientific background,” explains David Feigman, provost and dean of the University of California School of Law, San Francisco. “Having an independent and neutral resource is invaluable.”
In December 2025, the manual was updated for the first time in 15 years with new chapters on computer science, artificial intelligence, and climate science.
The chapter on climate science was met with immediate backlash. In late January, 27 Republican state attorneys general sent a letter to the FJC asking it to remove a 90-page chapter on climate science, calling it “inappropriate” and “advocacy-based.”
FJC Director Robin Rosenberg responded on February 6, stating that the climate science chapter had been removed.
“I think it’s outrageous that it was removed. Manuals shouldn’t be defeated by political forces and shouldn’t be influenced by the politics of the moment.”
Scientists and legal experts voiced opposition to the decision, arguing that its removal would “deprive judges of the resources they need to do their jobs.” The chapter’s authors published a defense of the removed material, and dozens of other contributors to the manual similarly condemned the decision. National Academy of Sciences President Marcia McNutt defended the chapter in a letter to the Academy of Sciences. wall street journal: “A draft of this chapter was reviewed by an oversight committee that included judges and scientists and was further evaluated by another group of judges and scientists who served as anonymous expert reviewers.” AGU issued a statement calling on the FJC, as well as the American Meteorological Society, to reinstate the chapter.
“I think it’s outrageous that it was removed,” said Nancy Gartner, a former federal judge in the District of Massachusetts and now a senior lecturer at Harvard Law School. “The manual should not be overpowered by political forces, it should not be influenced by the politics of the day. The whole idea is that the manual should be independent of political forces. And since the judges will be dealing with climate science issues, that should be in the manual.”
Increase in climate litigation
This reference manual was first published in 1994 and has been updated regularly since then. For example, in 2000 we added guides on medical testimony and engineering, and in 2011 we added chapters on neuroscience and mental health. Feigman said the addition of the climate science chapter is likely due to the increase in climate-related litigation and policy activity, especially in the past decade.
“I think it was probably added because the subject matter acquired special resonance and importance, just as other chapters were added,” he says. “There are a lot of cases surrounding climate change, so I think it’s essential for judges to understand the basic science of climate. It’s really just background information for judges to understand what the issues are beyond the case, and not necessarily what the issues are being raised in each individual case.”
Gartner said that’s exactly how he used the manual when he was a judge. “This manual details a much broader range of issues than lawyers sometimes do, so we use it to understand the context,” she said. “I would often read scientific evidence to supplement and sometimes replace what the lawyers were saying.”
Give equal space to the opposite view?
One of the criticisms leveled at this chapter by its opponents is that its authors, environmental law expert Jessica Wentz and climate scientist Radley Horton, are both affiliated with Columbia University’s Sabin Center for Climate Change Law.
“To our knowledge, Wentz and Horton did not consult any experts who might take a view inconsistent with Wentz and Horton’s concept of ‘consensus,'” the attorney general’s complaint states. They do not cite, for example, the names of the key experts in the Department of Energy’s recent report on climate change. ”
A Department of Energy (DOE) climate change report written by five climate change opponents has been widely criticized by the scientific community for downplaying the dangers of climate change. In January, a federal judge ruled that the DOE violated the law in issuing the report.
Gartner supports the practice of renowned experts who write each chapter of the manual. He said there is “no difference” between Wentz and Horton writing a chapter on climate and, say, the author of a chapter on medical testimony being affiliated with Georgetown University Law Center’s O’Neill Institute for National and Global Health Law.
“It’s like we’re in a time where we somehow think we have to give equal time to people who believe the earth is flat. So you’re not.”
“It seems like we’re at a point where we have to give some form of equal time to people who believe the earth is flat,” she says. “So, that’s not the case. There are some issues that simply cannot be considered.”
Faigman explained that each chapter in the manual is written by an expert in the field, but the content of each chapter has been subject to extensive peer review and editing by experts in the relevant subject matter. He added that, in his opinion, it makes sense to choose chapter authors who are highly trained in their respective scientific fields and who present the material in a balanced way, and not necessarily in a way that presents all points of view.
“To take perhaps another controversial example, if you’re asking about the effectiveness of measles vaccines, you’re probably asking people who have a basic understanding of the clinical research underlying measles vaccines,” he said. “There is no obligation to include anti-vaxxers.”
The road ahead
NASEM has chosen to keep this chapter, at least for the time being, in the version of the manual published on its website. However, Gartner said most judges refer to the FJC version and may not have seen this chapter.
“The purpose of the FJC manual is to make it readily available to judges so that they do not consult other authoritative sources,” she said.
Feigman said he was encouraged by the fact that NASEM retains a role as a scientific authority that FJC does not have. He said removing the chapter could garner more attention than it would have otherwise.
He also said he could foresee the manual itself becoming a legal issue. For example, one judge may cite its authority, another may question it, and the validity of the chapter itself may be challenged in court.
“At the end of the day, truth and science are indisputable,” Feigman said. “Denying climate change doesn’t change the fact that the climate is changing. While it may serve the immediate political moment, trying to ignore climate impacts is not very helpful to American society or the judiciary.”
—Emily Gardner (@emfurd.bsky.social), Deputy Editor
