California Attorney General Rob Bonta joined a multistate coalition of attorneys general in opposing a U.S. Global Change Research Program proposal to amend the Fifth National Climate Assessment. The coalition’s comment letter argues that the proposed changes would be arbitrary and capricious—and therefore unlawful—if adopted and relied upon by federal agencies.
The proposal would retroactively modify the assessment, known as NCA5, to limit federal agencies’ interpretation and use of findings based on certain worst-case, high-emissions scenarios. Those scenarios describe a future in which annual greenhouse gas emissions continue to rise and no transition to renewable energy or other climate-mitigation policies occurs.
Federal law requires the U.S. Global Change Research Program to prepare a National Climate Assessment every four years. NCA5, the latest assessment, was released in November 2023 and provides an overview of current climate science along with adaptation and mitigation strategies across a range of subjects.
The program published notice of the proposed amendment on August 25, 2026. According to the California Attorney General’s Office, the amendment does not identify who prepared or reviewed it, appears not to have undergone peer review, and does not appear to have been prepared with the involvement of the National Academies of Sciences, Engineering, and Medicine. The office also said the document has characteristics of material developed using artificial intelligence, raising concerns about its reliability.
The coalition also objected to the public-review process, including a word limit on comments, a 15-day comment period for amendments to the 2,000-page assessment, and a statement that comments would not receive a response. The letter characterizes the proposal as failing federal information-quality requirements applicable to National Climate Assessments.
Bonta urged the program to rescind the proposal and said he would continue supporting scientific findings backed by peer review. The Attorney General’s Office described the amendment as part of broader Trump administration actions affecting NCA5, including canceling contracts, dismissing scientists, reducing the U.S. Global Change Research Program, and removing National Climate Assessments from federal websites.