Word just came down that the Supreme Court has ruled against the Bush administration in the landmark global warming case of Massachusetts v. EPA. The ruling was 5-4, with conservatives dissenting and the crucial vote of Anthony Kennedy going with the … non-conservatives. Background on the case here, here, here, and here.

The court addressed three questions:

Do states and environmental groups have standing to sue EPA?

(To show legal standing, states had to show they would be harmed by the excess global warming that would occur without EPA regulations. This was the real sticking point, and it was at the center of the conservative justices’ dissent.)

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Verdict: Yes.

Does the EPA have the right to regulate CO2 emissions as a pollutant under the Clean Air Act?

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Verdict: Yes.

Can the EPA choose not to regulate CO2 emissions at its own discretion?

Verdict: The court told EPA to … reconsider its claim that it has that discretion. Said majority opinion writer Justice John Paul Stevens: “EPA has offered no reasoned explanation for its refusal to decide whether greenhouse gases cause or contribute to climate change.” The court also offered EPA a laundry list of reasons why it should so regulate. [Update: That was wrong — what the court did is reject what it called the EPA’s “laundry list” of crappy reasons not to regulate.] In effect, the court put enormous pressure on EPA to regulate.

This is a huge, huge deal. The proximate effect is that California’s pioneering efforts against climate change are safe from federal interference.

More broadly, the Supreme Court has put the weight of the judicial branch of the federal government behind the effort to fight global warming. There is no longer a shred of doubt, if there was any left, that federal action is inevitable.

Bush’s isolation on this issue is now total. No one stands with him — not Congress, not the business community, not the religious community, not the public at large, not the courts. Only James Inhofe. That’s a grim assessment indeed.

(More background on the case from Environmental Defense, one of the plaintiffs.)

(Still more from ThinkProgress, and more yet from SCOTUSblog.)

(The Wall Street Journal energy blog has a round-up of reactions to the ruling.)

(More from Carl Pope, dissing Scalia’s dissent, and from Jonathan Adler, supporting Roberts’ dissent on the subject of standing.)

(More from Roger Pielke Jr.)