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In a 5-4 decision delivered today, the U.S. Supreme Court upheld, for the most part, the Environmental Protection Agency’s power to regulate greenhouse gas emissions.

The EPA’s authority to regulate emissions was established in a 2007 Supreme Court decision, which said that the agency was obliged under the Clean Air Act to limit emissions of carbon dioxide and other planet-warming pollutants. That decision wasn’t up for debate, Chief Justice John Roberts stated during oral arguments. This case dealt with how, exactly, the EPA could regulate companies that produce emissions.

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Large emitters like power plants are still subject to EPA regulations.

Under the EPA’s proposed regulations, any company that is building a new facility or addition that would emit greenhouse gases would have to apply for a permit. This part the court struck down. Companies that are already subject to permits for other pollutants, however, which include those that run power plants, would have to apply for permits. Justice Antonin Scalia estimated the ruling would reduce the number of stationary emitters (read: not cars) subject to regulation from 86% to 83%. The EPA agreed with that assessment.

Richard Wolf, reporting for USA Today:

The decision only removed one method the administration uses to regulate greenhouse gas emissions at power plants, refineries and other stationary sources, leaving other methods in place. That likely means that the administration will move ahead with its new regulations on existing coal-fired power plants, setting off a new wave of lawsuits. “Little in today’s opinion casts any new doubts upon the legal validity of the recent regulations proposed by the Obama administration earlier this month,” said Bruce Huber, a University of Notre Dame associate law professor. “However, in the long run, congressional action will be required if the EPA is to regulate greenhouse gases from all sources nationwide.”

Currently, the Clean Air Act requires compliance from any facility that spews more than 100 pounds of a pollutant per year. For some emissions, like lead and other toxic metals, this threshold is sufficient. But the average car, for example, produces 10,472 pounds of carbon dioxide per year . The 100 pound limit would require the EPA to regulate just about everything, which currently isn’t feasible.

The agency proposed raising the threshold for permitting to 75,000 pounds per year, but changing the Clean Air Act in such a way, the court said, is something only Congress can do.

The EPA’s most recent proposal calls for a 30% reduction in greenhouse gas emissions below 2005 levels by 2030, a modest amount. Most climate scientists say that, to avoid significant and potentially dangerous warming, we will have to reduce emissions by 80% below the much-lower 1990 levels by 2050.