The Supreme Court ruled in a 5-4 decision today that carbon dioxide and other greenhouse gasses are pollutants under the Clean Air Act and the EPA has the authority to regulate them. The Wikipedia entry for Massachusetts v. Environmental Protection Agency has already been updated to reflect the ruling.
Writing for the majority, which also included Justices Kennedy, David Souter, Ruth Bader Ginsburg and Stephen Breyer, Justice John Paul Stevens gave the court's decision that:
"...it is clear that petitioners’ submissions as they pertain to Massachusetts have satisfied the most demanding standards of the adversarial process. EPA’s steadfast refusal to regulate greenhouse gas emissions presents a risk of harm to Massachusetts that is both 'actual' and 'imminent'..."
Having established that Massachusetts had legal standing as a plaintiff in this case, the court ruled:
"EPA has offered no reasoned explanation for its refusal to decide whether greenhouse gases cause or contribute to climate change. Its action was therefore 'arbitrary, capricious...or otherwise not in accordance with law.' 42 U.S.C.§7607(d)(9)(A). We need not and do not reach the question whether on remand EPA must make an endangerment finding, or whether policy concerns can inform EPA's actions in the event that it makes such a finding. Cf. Chevron U.S.A. Inc. v. Natural Resources Defense Council, Inc., 467 U.S. 837, 843-844 (1984). We hold only that EPA must ground its reasons for action or inaction in the statute."
As I wrote about this case last December, this is one to watch. The court ruled that greenhouse gases are pollutants under Section 202 (a)(1) of the Clean Air Act, 42 U.S.C. § 7521 (a)(1). Justice Stevens said EPA's "alternative basis for its decision - that even if it has statutory authority to regulate greenhouse gases, it would be unwise to do so at this time - rests on reasoning divorced from the statutory text." EPA has a wealth of data on US Greenhouse gas emissions, including this Draft Inventory of US Greenhouse gas emissions and sinks published in February, that it can turn to in support of its future action to regulate such emissions. If it chooses not to act, EPA's words will be cited by those calling for such limitation.
The case now goes back to the lower court.