3 November 2017: A report published by the US Global Change Research Program (USGCRP) on the eve of the opening of the UN Climate Change Conference in Bonn, Germany, provides an updated and detailed analysis of how climate change is affecting weather and climate across the US and the globe. Titled ‘Climate Science Special Report’ (CSSR), the report integrates and evaluates findings on climate science, discusses uncertainties associated with these findings, analyzes current trends, and projects major trends to the end of this century.

The CSSR finds that human activities, especially greenhouse gas (GHG) emissions, are the dominant cause of the observed warming since the mid-20th century. It also explains that thousands of studies have documented changes in: surface, atmospheric and oceanic temperatures; melting glaciers; diminishing snow cover; shrinking sea ice; rising sea levels; ocean acidification; and increasing atmospheric water vapor.

The CSSR provides the foundation for the NCA4 second volume, which is titled, ‘Climate Change Impacts, Risks, and Adaptation in the US,’ and will be released in December 2018.

The report also finds that, inter alia: global average sea levels are expected to continue to rise by at least several inches in the next 15 years and by 1-4 feet by 2100; heavy rainfall is increasing in intensity and frequency across the US; heatwaves have become more frequent in the US, while extreme cold temperatures and cold waves are less frequent; the incidence of large forest fires in the western US and Alaska has increased; and earlier spring melt and reduced snowpack are already affecting water resources in the western United States.

The CSSR describes the possibility of unanticipated changes such as compound events, where multiple extreme climate events occur simultaneously or sequentially, and critical threshold, or “tipping point” events, where some threshold is crossed in the climate system that leads to large impacts.

Finally, the report discusses advances in scientific understanding and developments in global policy since NCA3 in 2014 related to, inter alia: how climate change may affect specific types of extreme events in the US; high-resolution global climate model simulations that provide a more realistic characterization of intense weather systems, including hurricanes; the severity of the impacts of ocean acidification, warming and oxygen loss; and incorporation of geographic variation in sea level rise projections.

The report is the first of two volumes of the Fourth National Climate Assessment (NCA4), a quadrennial assessment prepared by the USGCRP and submitted to the US President and the Congress. The CSSR provides the foundation for the NCA4 second volume, which is titled, ‘Climate Change Impacts, Risks, and Adaptation in the US,’ and will be released in December 2018. The National Oceanic and Atmospheric Administration (NOAA) serves as the administrative lead agency for the preparation of NCA4. [CSSR Landing Page] [About the CSSR] [Climate Science Special Report] [Letter from USGCRP Acting Chair and Executive Director] [NCA4 Website]