National Climate Assessment

• 1. Introduction

  ›

  The National Climate Assessment is a federal research initiative unlike almost any other in American science. Every few years, hundreds of researchers, government officials, and public voices gather to answer a single question: what is climate change actually doing to the United States, right now and in the decades ahead? The answers carry legal weight. They inform policy at every level of government. And they are mandated by law.

  The program traces its origins to the Global Change Research Act of 1990, a law that requires the federal government to deliver a report to the President and Congress integrating the best available science on how a changing climate affects the natural environment, agriculture, energy, transportation, human health, and biological diversity. That report must also project major trends for the subsequent 25 to 100 years.

  Since the first report appeared in 2000, five assessments have followed, each involving larger teams and more public scrutiny than the last. But in 2025, work on the sixth assessment stopped entirely. The scientists were dismissed. The funding was cut. And on the 30th of June, 2025, the government website hosting every past report was taken down. What the NCA is, how it came to matter so much, and what happened to it are questions worth examining closely.

• 2. The Law Behind the Science

  ›

  The Global Change Research Act of 1990 is the foundation everything else rests on. Under that law, the federal government is required to produce reports that do not merely summarize findings but integrate, evaluate, and interpret them. The law names specific sectors: agriculture, energy production and use, land and water resources, transportation, human health and welfare, and biological diversity. Climate change must be analyzed across all of them.

  Responsibility for producing these reports falls to the U.S. Global Change Research Program, known as USGCRP, a collaboration of thirteen federal agencies and departments. Those agencies span the full range of government: NOAA, NASA, the EPA, the Departments of Agriculture, Commerce, Defense, Energy, Health and Human Services, Interior, State, and Transportation, along with the National Science Foundation and the Smithsonian Institution.

  The law also specifies a timeline. Reports are required every four years, though in practice the interval has stretched longer. The law does not give the executive branch the option to simply stop. It mandates the work. That legal reality became increasingly significant when, in 2025, a presidential administration chose to halt the process anyway.

• 3. Building the Assessment

  ›

  Between 2002 and 2009, during a period when USGCRP operated under the name U.S. Climate Change Science Program, the program produced 21 Synthesis and Assessment Products to keep the research pipeline moving between full assessments. These products addressed specific sectors and questions rather than the comprehensive national picture the full NCA provides.

  For the Third National Climate Assessment, released publicly in May 2014, the coordination effort grew dramatically. More than 300 authors contributed, drawn from academia, local and state and tribal and federal governments, and the private and nonprofit sectors. A 60-member Federal Advisory Committee called the National Climate Assessment and Development Advisory Committee, or NCADAC, oversaw the draft and made recommendations throughout.

  Public participation was built into the process. After the draft was released for public comment on the 14th of January, 2013, more than 4,000 comments arrived from 644 individuals and organizations before the comment period closed on the 12th of April, 2013. Those commenters included government employees, educators, students, nonprofit workers, and members of the general public. The National Research Council, part of the National Academy of Sciences, conducted a separate parallel review and submitted its own feedback.

  To reach beyond the immediate scientific community, USGCRP began recruiting in 2011 for NCAnet, a network of organizations working to engage producers and users of assessment information across the country. NCAnet was formally registered at the Federal Register on the 13th of April, 2012.

• 4. What the Reports Found

  ›

  The first report, released in 2000 and titled "Climate Change Impacts on the United States: the Potential Consequences of Climate Variability and Change", organized its findings across roughly 20 regional studies. Each regional study involved dozens of scientific and academic experts alongside representatives from industry and environmental groups. The National Assessment Synthesis Team that produced it concluded, in their 2001 assessment, that natural ecosystems appear to be the most vulnerable to the harmful effects of climate change.

  The Fourth National Climate Assessment, produced across two volumes in October 2017 and November 2018, stated its central finding with unusual directness. Volume 1 reported that it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the middle of the twentieth century, and that for the warming over the last century there is no convincing alternative explanation supported by the extent of the observational evidence.

  Volume 2 of the Fourth Assessment, released on the 23rd of November, 2018, turned to consequences. Without substantial and sustained global mitigation and regional adaptation efforts, the report stated, climate change is expected to cause growing losses to American infrastructure and property and impede the rate of economic growth over this century. The report also stated that human health and safety and American quality of life is increasingly vulnerable to the impacts of climate change. The team that produced the Fourth Assessment included roughly 1,000 people, with about 300 leading scientists, approximately half from outside the government.

  The Fifth Assessment was published on the 14th of November, 2023, continuing the pattern of ever-larger collaborative efforts.

• 5. Advisory Committees and Their Fates

  ›

  The National Assessment Synthesis Team, known as NAST, was formed in 1998 under the Subcommittee on Global Change Research. Its founding mandate was to broadly design and conduct national efforts to assess the consequences of climate variability and climate change for the United States. Membership drew from government, academia, and private enterprise. The first co-chairs were Dr. Jerry M. Melillo of the Marine Biological Laboratory in Woods Hole, Massachusetts, Tony Janetos, and Thomas Karl. Administrative support came from the University Corporation for Atmospheric Research, sponsored by the National Science Foundation.

  The NCADAC, the 60-person advisory committee that guided the Third Assessment, was established by the Department of Commerce in December 2010 under the Federal Advisory Committee Act of 1972, and was supported through NOAA. It was sunsetted in the fall of 2014 after the Third Assessment was complete.

  A successor body, the Advisory Committee for the Sustained National Climate Assessment, was established in 2015 and chaired by Richard H. Moss. On the 20th of August, 2017, the first Trump administration sunsetted that fifteen-member committee. NOAA stated at the time that the disbandment would not impact the completion of the Fourth National Climate Assessment, which did proceed. A separate fifteen-member advisory committee had been disbanded by the first Trump administration on the 18th of August, 2017, tasked with writing concrete guidance based on assessment findings.

• 6. The Sixth Assessment Falls Apart

  ›

  Under the regular five-year schedule, the Sixth National Climate Assessment was due in 2028. Work was underway. Contracts were in place. Then, on the 28th of April, 2025, the second Trump administration fired all authors, scientists, and contributors who had been working on NCA6. The administration had earlier canceled a contract with ICF International that provided technical consulting for the project.

  The scope of the report was described as being re-evaluated, though no revised direction was publicly announced. On the 30th of June, 2025, the government website that had provided public access to all previous National Climate Assessment reports was taken down, removing decades of federally produced climate science from official government hosting.

  In late 2025, the organization climate.us established a website to host the Fifth National Climate Assessment, preserving access outside of government servers.

  On the 29th of July, 2025, the Energy Department released a separate report on climate change. Scientists widely criticized that report for an abundance of errors and denial of the scientific consensus on climate change. The report was written by prominent climate deniers who had been given government jobs. The contrast between that document and the thousands of peer-reviewed contributors who built the NCA over 25 years reflects the distance between the two approaches to federal climate science.