In Fourth National Climate Assessment (NCA4) Volume 1, released in October 2017, entitled "Climate Science Special Report" (CSSR), researchers reported that "it is extremely likely that human activities, especially emissions of greenhouse gases, are the dominant cause of the observed warming since the mid-20th century. For the warming over the last century, there is no convincing alternative explanation supported by the extent of the observational evidence." A 2018 CRS cited the October 2017 CSSR: "Detection and attribution studies, climate models, observations, paleoclimate data, and physical understanding lead to high confidence (extremely likely) that more than half of the observed global mean warming since 1951 was caused by humans, and high confidence that internal climate variability played only a minor role (and possibly even a negative contribution) in the observed warming since 1951. The key message and supporting text summarizes extensive evidence documented in the peer-reviewed detection and attribution literature, including in the IPCC Fifth Assessment Report." Volume 2 entitled "Impacts, Risks, and Adaptation in the United States" was released on November 23, 2018. According to Volume II, "Without substantial and sustained global mitigation and regional adaptation efforts, climate change is expected to cause growing losses to American infrastructure and property and impede the rate of economic growth over this century." The National Oceanic and Atmospheric Administration (NOAA) was "administrative lead agency" in the preparation of the Fourth National Climate Assessment. According to NOAA, "human health and safety" and American "quality of life" is "increasingly vulnerable to the impacts of climate change". The USGCRP team that produced the report included thirteen federal agencies— NOAA, the DOA, DOC, DOD, DOE, HHS, DOI, DOS, DOT, EPA, NASA, NSF, Smithsonian Institution, and the USAID—with the assistance of "1,000 people, including 300 leading scientists, roughly half from outside the government."
