Sometimes the proximity of two unrelated events is so great that to call them coincidental seems hard to believe.

So it is with the U.S. Supreme Court's decision telling the federal government to reconsider its refusal to regulate vehicle emissions and the almost simultaneous release of a comprehensive, highly disturbing study by the world's leading panel on climate change.

The high Court's 5-4 opinion clears the way for more aggressive steps to respond to global warming. It also affirms the states' rights to help protect our environment.

As if to put an exclamation point on the wisdom of that legal decision, the scientific study documented climate changes already taking place in the world and predicted a particularly harsh drought impact for our American Southwest. The Supreme Court's ruling clears an obstacle to action at the precise moment the climate study demands action.

The Court ruled that the federal government, contrary to the Bush Administration's position, has the authority under the Clean Air Act to regulate carbon dioxide and other greenhouse gases produced by motor vehicles.

The case, Massachusetts v. Environmental Protection Agency, opens the door for more aggressive actions by both state and federal governments to limit car emissions. The Court knocked down the key legal argument against California's adoption of tighter emission standards and should encourage Arizona and other states to pass them as well.

The Court's decision agreed with points I made in a friend-of-the-court brief filed in the Massachusetts case last year. Arizona’s brief argued that the EPA's narrow interpretation of the Clean Air Act was wrong and contrary to the public interest. It further contended that the states had a duty to act to help protect citizens from the potentially devastating impact of climate change. If the EPA chose not to exercise its power under the law to regulate heat-trapping emissions, the states had the right to ask the courts to demand the agency do its job.

Damages suffered by Arizona and other states from climate change are underscored by the new report from the Intergovernmental Panel on Climate Change. The report made it clear that global warming's impact will not be the same throughout the world. Some regions stand to benefit from warmer temperatures and a longer growing season. But the climate in Arizona and other Southwestern states will become much hotter and drier, increasing the probability of droughts and severe forest fires. The federal government's failure to regulate greenhouse gases will be felt more severely in Arizona than almost anywhere else in the country.

It remains unclear whether the Bush Administration will actually use its newly clarified authority to reduce greenhouse gas emissions. But it is abundantly clear that if more steps are not taken soon to respond to global climate change, Arizona will be among the places paying the biggest price. Even without federal leadership, the Supreme Court has invited the states to come off the sidelines and start shaping their future.

Terry Goddard