01:00 AM EDT on Saturday, July 8, 2006

Whether the nine U.S. Supreme Court justices have had time to take in An Inconvenient Truth is anyone's guess. But they may not have needed Al Gore's filmic alarm to sense that the looming dangers of global warming demand attention. By recently agreeing to hear an important clean-air case next term, the court signaled its willingness to address one of the most contentious and complex issues of our time. The result could be one of the most significant environmental rulings in years.

Rhode Island, Massachusetts and Connecticut are among the dozen states pressing the federal government to control emissions of carbon dioxide: the chief "greenhouse" gas believed responsible for global warming. In the United States, motor vehicles cause about 50 percent of these emissions; power plants cause roughly 40 percent.

In 1999, along with environmental groups and a handful of cities (New York, e.g.), the states sued, arguing that the federal Environmental Protection Agency was required to regulate carbon dioxide. Under the Bush administration, the agency resisted, noting that the Clean Air Act did not name carbon dioxide as a regulated pollutant. The states countered that carbon dioxide is harmful under the terms of the act, and thus, implicitly, must be controlled.

Appeals-court judges split when they ruled on the case last summer. One, Judge A. Raymond Randolph, said that even if the EPA had the authority to regulate carbon-dioxide emissions, it could choose not to. Costs could come into play, for instance, as could technological limitations or scientific uncertainty.

The Bush administration has long resisted addressing this issue, wrongly leaving the states to take on what should be a national fight. Although the president admitted last month that global warming was a "serious problem," he continues to favor voluntary approaches to curbing emissions. But emissions continue to grow -- not only here but also abroad, especially in rapidly industrializing China and India.

How the United States ultimately responds to this issue is crucial, not just for Americans but for the world. U.S. vehicles spew 45 percent of the globe's automotive carbon-dioxide emissions -- far more than our share. Reducing these emissions would appear a vital piece of any effort to slow the effects of global warming.

The Supreme Court has never addressed the question of climate change in a significant way. Commendably, the court now seems to see the importance of this case -- and the importance of not putting it off.