WASHINGTON -- In the most significant global warming case to reach its front doors, the Supreme Court on Monday blocked a major lawsuit brought by states and environmental groups against five large power companies they accused of creating a public nuisance because of carbon dioxide emissions.

The court ruled 8-0 that the authority to set standards for reducing emissions lies with the Environmental Protection Agency, under air pollution rules established by the Clean Air Act. The court said just because the EPA hasn't acted yet doesn't mean that its authority is no longer valid.

The Clean Air Act "provides a means to seek limits on emissions of carbon dioxide from domestic power plants -- the same relief the plaintiffs seek by invoking federal common law. We see no room for a parallel track," reads the order written by Justice Ruth Bader Ginsburg.

"If EPA does not set emissions limits for a particular pollutant or source of pollution, states and private parties may petition for a rulemaking on the matter, and EPA's response will be reviewable in federal court," the decision continues.

Justice Sonia Sotomayor sat out the case because she had considered it while serving on the 2nd Circuit Court of Appeals, which overturned a lower court ruling in favor of the plaintiffs.

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The states claim the power companies have caused irreparable environmental harm by allowing its plants to produce excessive levels of carbon dioxide. They claim people have died because of the pollution and others have been directly impacted by the resulting smog, decreased fresh water supplies, land erosion and rising sea levels.

The lawsuit targeted the five largest emitters of carbon dioxide in the United States, four private companies and the federal Tennessee Valley Authority. It was brought under a federal common law claim, arguing that the courts could intervene in a case where activities in one state -- like the creation of pollution -- cause a nuisance in another state.

The court noted that EPA says it will decide by next year whether to order utilities to cut emissions of carbon dioxide, a greenhouse gas -- that deadline was set after many of the same plaintiffs sued to have EPA set the rule.

A victory for the states and against the energy providers could have meant dramatic changes in the energy market and other industries. But the merits of the case rested on the separation of powers argument. The Obama administration sided with the power companies arguing that the political branches should take the lead in regulating matters, a decision that didn't sit well with environmental groups.

"We're disappointed that the Obama administration would stand before the court and argue to limit access to the courts," John Kostyck, vice president, National Wildlife Federation, told Fox News after the case was heard in April. While Kostyck credited the EPA with doing good work the past two years in fighting global warming, he said the government has dragged its feet when it comes to cracking down on existing power plants.

Click here to read the ruling.

Fox News' Lee Ross contributed to this report.