What a difference a change in administrations makes. Following the November Presidential elections, it was considered a foregone conclusion that the regulation of CO2 and its greenhouse gas (GHG) kin, at least from motor vehicles, was simply a matter of time, in light of the 2007 ruling in Massachusetts et al. vs EPA (549 US 497 [2007]; Front Ecol Environ 5[5]: 279). In that decision, the US Supreme Court found that, “greenhouse gases fit well within the Clean Air Act's [CAA] capacious definition of air pollutant”. The Supreme Court ordered the Environmental Protection Agency (EPA) to determine specifically if emissions of GHGs from new automobiles pose a danger to human health. It is important to remember that the Court did not rule on whether CO2 emissions cause global warming, but on whether scientific uncertainty was a valid reason for the EPA not to regulate a pollutant under the CAA. The Bush Administration sided with the uncertainty argument; the Obama Administration, however, is taking the opposite viewpoint. In November 2008, the EPA Environmental Appeals Board, in In re: Deseret Power Electric Cooperative, reviewed a construction permit for a new waste-coal-fired electrical generation unit in Bonanza, UT. The Board ruled that the EPA had no valid reason for refusing to limit CO2 emissions from new coal-fired power plants. The ruling, practically speaking, suggests that all new and proposed coal plants are required to address their GHG emissions. The most momentous event, however, was held on April 17, when Lisa P Jackson, the new EPA Administrator, signed the Proposed Endangerment and Cause or Contribute Findings for Greenhouse Gases Under Section 202(a) of the Clean Air Act. Jackson then announced the beginning of a 60-day public comment period, prior to a proposed rule-making, based on a scientific analysis and endangerment finding that would seek to regulate six GHGs – CO2, methane, nitrous oxide, hydrofluorocarbons, perfluorocarbons, and sulfur hexafluoride – that pose a potential threat to public health. The announcement was not accompanied by a draft rule seeking to limit GHG emissions directly; rather, the EPA indicated that the comment period was important to an eventual regulatory decision, and that drafting of proposed standards would proceed simultaneously. Notably, the EPA stated that the increasing atmospheric levels of the six GHGs are “the unambiguous result” of human activities and are responsible for more intense heat waves, storms, and wildfires; increased flooding and droughts; and other “effects on public health and welfare”. The document further states, “The heating effect caused by the human-induced buildup of greenhouse gases in the atmosphere is very likely the cause of most of the observed global warming over the last 50 years”. Under Section 202(a) of the CAA, the EPA must decide (1) if GHGs may reasonably be anticipated to endanger public health or welfare, and (2) whether, in the Administrator's judgment, emissions of an air pollutant from new motor vehicles cause or contribute to GHG pollution. If the EPA finds in the affirmative to both questions, standards must be issued. While this proposal deals with cars and trucks, other GHG emission sources can't be far behind. The Obama Administration would prefer the more favorable political course of having Congress pass legislation that would lead to revisions in the CAA through the enactment of a cap-and-trade program. The EPA, it seems, is essentially taking the position that, if Congress doesn't act, they will. So industry can select the proverbial “door #1” and install best-available control technology in areas where GHGs would be regulated as pollutants, or choose “door #2” and introduce some sort of nationwide method of capping GHGs, and allow market forces to dictate a market for such pollutants. Frank O'Donnell, president of Clean Air Watch, described this impending game of “chicken” as: “If business groups, such as the US Chamber of Commerce, continue to oppose Congressional action, they ought to ask themselves…‘Do I feel lucky?' ” Discussion drafts of legislation have already begun to circulate, including the Waxman-Markey American Clean Energy and Security Act of 2009, a complex bill involving carbon control and elimination. So progress is being made, albeit slowly. Profound environmental issues don't usually lend themselves to humor, but we can all hope that a headline that once appeared in The Onion – “Fall cancelled after 3 billion seasons…a beloved classic comes to an end” – will generate future chuckles rather than appreciation for its prescience. And then there is: “How many global warming skeptics does it take to change a light bulb? None. It's too early to say if the light bulb needs changing.”