On February 28 and 29, the D.C. Circuit Court of Appeals heard oral arguments in a series of challenges to the [EPA’s] regulation of [GHGs] under the Clean Air Act, far-reaching litigation spanning dozens of parties and at least four separate rules. Decisions from the panel of Judges David Sentelle, David Tatel and Janice Rogers Brown are expected later this year. The rare, two-day argument began with a challenge to EPA’s December 7, 2009 finding that emissions of six GHGs, including carbon dioxide, “may reasonably be anticipated both to endanger public health and to endanger public welfare.” This “endangerment finding” is the cornerstone of all subsequent action by EPA.