President George H.W. Bush signed the Global Change Research Act of 1990 into law on the 16th of November 1990. This legislation established the United States Global Change Research Program with a clear mandate to understand and respond to global change.
Thirteen federal agencies comprised the USGCRP team including NASA, NOAA, and the Department of Energy. The National Oceanic and Atmospheric Administration served as the administrative lead agency for the NCA4 preparation.
Researchers reported that it is extremely likely that human activities are the dominant cause of observed warming since the mid-20th century. No convincing alternative explanation exists supported by the extent of observational evidence for the warming over the last century.
The White House announced on November 21 that it would release the NCA4 findings on Black Friday. President Trump told reporters he had seen and read some of the report but stated he does not believe it.
The Union of Concerned Scientists described how the 1,500-page report was based on the best available science. Brenda Ekwurzel served as both a NCA4 Report Author and Senior UCS Climate Scientist during this period.