4th U.S. National Climate Assessment: What Is It?



The U.S. National Climate Assessment is a regular science report by 13 federal agencies, mandated by Congress to inform the nation and our government about climate change.

The Fourth National Climate Assessment (NCA4), Volume II documents how climate change impacts people in regions and sectors across the United States, and how society is responding to climate change. (NCA4 Volume 1 “Climate Science Special Report” was released in 2017, and addressed the causes and consequences of climate change for the physical world.)

The Global Change Research Act of 1990 requires that a report must be presented to the President and the Congress every four years that gives a thorough overview of the status of climate science and climate change’s widespread impacts. The National Climate Assessment (NCA) is conducted to meet this requirement, and this is the fourth version of the report.

On the NCA process

  • The NCA goes through multiple rounds of peer-review, incorporating and addressing edits and comments from the general public as well as the National Academies of Science, among others. These thousands of comments were carefully considered, and NCA authors’ responses will be published online.
  • The NCA process relies on consensus, and as a result, the assessment’s findings reflect very conservative estimates of climate change impacts as representatives from both oil companies and environmental groups agree to the assessment’s findings.
  • The NCA findings are presented by the National Climate Assessment Development Advisory Committee (NCADAC), a 60-member federal advisory committee made up of notable scientists, business leaders, and other experts.
  • The content of the assessment is written by over 300 scientists and other experts from academia; local, state, and federal government; the private sector; and the non‐profit sector.
  • While the assessment is being released by the Trump Administration, what Congress and the Administration do as a result of the assessment is not part of the NCA process.
  • Hundreds of meetings and workshops have been either conducted or attended by NCA staff over the last four years to discuss the assessment.
  • Both the recently released IPCC 1.5 special report and the National Climate Assessment represent a consensus view of climate science, but the NCA goes into greater detail on climate impacts in regions of the United States, as well as interactions between climate and extreme weather in those regions.

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