The Climate Science Special Report: An Overview (Invited Presentation)

As part of the process in developing the 4^th National Climate Assessment, the Climate Science Special Report (CSSR) has been developed to provide a comprehensive assessment of the science underlying the changes occurring in the Earth’s climate system, with a special focus on the United States. The CSSR confirms prior assessments in concluding that the climate on our planet, including the United States, is changing, and changing rapidly. Observational evidence for a changing climate abounds, from the top of the atmosphere to the depths of the oceans. Documented changes include surface, atmospheric, and oceanic temperatures; melting glaciers; disappearing snow cover; shrinking sea ice; and rising sea level. Severe weather is becoming more intense. Heatwaves have become more frequent in the United States since the 1960s, while extreme cold temperatures and cold waves are less frequent. Heavy rainfall is increasing in intensity and frequency across the United States and globally. All of these trends are expected to continue. The Earth’s climate is projected to continue to change over this century and beyond. As a result, global average sea levels are expected to continue to rise. Many lines of evidence demonstrate that it is extremely likely (95% or greater likelihood) that human activities have been the dominant cause of the observed warming since the mid-20th century. This presentation provides an overview of the findings from the CSSR.