Friday’s report, the fourth National Climate Assessment, is the latest in a line of federal research into climate change. Mandated by the Global Change Research Act of 1990, it seeks to assess the environmental, economic, and health and safety consequences of climate change. It builds on a 2017 report in which federal scientists found “it is extremely likely that human influence has been 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.”