For more than three decades, climate change has been a focal point for science, media and politics. While the contributions of greenhouse gas (GHG) emissions to climate change are well understood, the Environmental Protection Agency (EPA) has been unable to widely regulate them. This article discusses some of the impediments to the EPA’s regulation of GHG emissions.

More than 15 years ago, the U.S. Supreme Court in Massachusetts v. Environmental Protection Agency, 549 U.S. 497, 528 (2007), held that the definition of “air pollutant” in the federal Clean Air Act (CAA) was broad enough to authorize the EPA to regulate GHG emissions from new motor vehicles if the EPA found that such emissions may reasonably be anticipated to endanger public health or welfare. Seizing on this newfound authority, the EPA quickly issued a finding that GHG emissions (a combination of carbon dioxide, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride) threatened public health and welfare of current and future generations. This finding is commonly known as the “Endangerment Finding.” Since issuing the Endangerment Finding in 2009, the EPA has made numerous attempts to regulate GHG emissions pursuant to its existing CAA authority, with varying degrees of success.