Short answers, pulled from the story.
The Fourth National Climate Assessment, or NCA4, is a congressionally mandated 1,500-page report produced by the U.S. Global Change Research Program. It was published in two volumes: the "Climate Science Special Report" in October 2017, and "Impacts, Risks, and Adaptation in the United States" on the 23rd of November, 2018. It was the fourth in a series that began with NCA1 in 2000, following reports in 2009 and 2014.
The Fourth National Climate Assessment stated it is "extremely likely" that human activities, especially greenhouse gas emissions, are the dominant cause of observed warming since the mid-20th century. Researchers reported high confidence that more than half of the global mean warming since 1951 was caused by humans, with internal climate variability playing only a minor role and possibly even a negative contribution.
The Fourth National Climate Assessment projected that without substantial mitigation, annual losses in some sectors of the U.S. economy could reach hundreds of billions of dollars by the end of the century. A 2017 study in the journal Science, cited in the report, estimated those damages in relation to rising global mean surface temperatures.
The Trump administration released NCA4 on the 23rd of November, 2018, a month before its expected date, which fell on Black Friday. Steven Milloy, a climate-change denier who served on Trump's EPA transition team, confirmed the strategy: the administration chose that day "on a day when nobody cares, and hope it gets swept away by the next day's news."
The Trump administration announced on the 20th of August, 2017, that it was dissolving the fifteen-person Federal Advisory Committee for the Sustained National Climate Assessment. That committee had been responsible for translating NCA scientific findings into policy actions states could use to reduce greenhouse gas emissions. New York Governor Andrew Cuomo reconvened a modified version in January 2018, chaired by Richard Moss of Columbia University's Earth Institute, though the states acknowledged it could not replace federal support for science or influence federal climate policy.
The Fourth National Climate Assessment was produced with the assistance of roughly 1,000 people, including about 300 leading scientists, approximately half of whom came from outside the government. The National Oceanic and Atmospheric Administration served as administrative lead agency, coordinating thirteen federal agencies in total, including the departments of Defense, Energy, and Interior, along with NASA, the EPA, and the Smithsonian Institution, among others.