CRS Report – U.S. Climate Change Policy. October 28, 2021: “The greenhouse gases (GHGs) in the atmosphere trap radiant energy, warming earth’s surface and oceans. Scientific assessments conclude that GHGs very likely have been the main driver of warming of the earth’s lower atmosphere since 1979. The most recent global assessment projected that surface temperature would continue to rise until at least mid-century even under the lowest GHG emission scenarios considered. A range of actions to mitigate GHG emissions and the risks of climate change (i.e., for adaptation or resilience) are underway or being developed on the international, national, and subnational levels. U.S. federal policymakers and stakeholders have different viewpoints regarding what, if anything, to do about future climate change and related impacts…U.S. climate change policy has involved actions implemented under various legal authorities. Prior to 2007, the federal government implemented voluntary programs to address climate change and regulatory programs that indirectly limited GHG emission increases from vehicles, appliances and equipment, and buildings. A shift toward direct regulation of GHG emissions occurred following the 2007 decision in Massachusetts v. EPA, in which the Supreme Court found that the Environmental Protection Agency (EPA) has authority to regulate GHG emissions from motor vehicles as air pollutants under the Clean Air Act. EPA subsequently issued rules to limit GHGs from various sources, although not all have been implemented. State and local governments have also taken a variety of actions, including emission controls on power plants and vehicles and building codes…”