In one of its most important environmental decisions in years, the Supreme Court ruled on Monday that the Environmental Protection Agency has the authority to regulate heat-trapping gases in automobile emissions. The court further ruled that the agency could not sidestep its authority to regulate the greenhouse gases that contribute to global climate change unless it could provide a scientific basis for its refusal.

The 5-to-4 decision was a strong rebuke to the Bush administration, which has maintained that it does not have the right to regulate carbon dioxide and other heat-trapping gases under the Clean Air Act, and that even if it did, it would not use the authority. The ruling does not force the environmental agency to regulate auto emissions, but it would almost certainly face further legal action if it failed to do so.

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