The Supreme Court agreed Monday to decide whether the federal government is required to control vehicle emissions of carbon dioxide, the principal greenhouse gas that scientists have linked to global warming. In accepting a petition from states, cities and environmental groups, the justices agreed to hear arguments on whether the Clean Air Act requires the Environmental Protection Agency to regulate carbon dioxide and other gases as air pollutants that may affect public health or the climate.

The case is one of the biggest environmental tests yet for the Bush administration, which has steadfastly opposed binding controls on greenhouse gases, instead calling for a voluntary approach by industry to curb emissions. "At stake in this case is nothing less than the survival of the earth as we know it," said Richard Blumenthal, the attorney general of Connecticut, which sued the government in 1999 along with New York, New Jersey, nine other states, three cities and a dozen environmental advocacy groups, including the Sierra Club, the Natural Resources Defense Council and Environmental Defense.

Ten other states and several industry groups joined the side of the administration. The case began in the final year of the Clinton administration, when a group of states and environmental organizations petitioned the E.P.A. to regulate carbon dioxide. After four years of study, the agency refused, concluding that the Clean Air Act did not require it to regulate emissions to prevent climate change.

The law, which was first written in 1963 and revised in 1970, before global warming emerged as a widespread concern, names many specific pollutants that the agency must regulate, including compounds released by cars, factories and power plants that form soot and smog. It does not name carbon dioxide, and in updating the law in 1990, Congress did not add the gas. The plaintiffs have argued that the laws definitions and other terms implicitly allow the regulation of carbon dioxide as a pollutant.

The administrations refusal to do so reflected a reversal of sorts for President Bush, who campaigned in 2000 on the need for federal emissions standards on a variety of air pollutants, including carbon dioxide. On Monday at the White House, Mr. Bush acknowledged that global warming was "a serious problem," but he also said there was some debate over whether it was caused by human activities. He called for using new technologies for environmental reasons and to wean the nation from its reliance on oil.

After the E.P.A. announced its refusal to regulate carbon dioxide emissions in 2003, the plaintiffs filed for review in the United States Court of Appeals for the District of Columbia Circuit. Last July, three judges issued three different opinions, which had the effect of supporting the agencys refusal by a 2-to-1 vote. Judge David B. Sentelle said the plaintiffs did not have standing to seek judicial review. Judge A. Raymond Randolph said that even if the agency had the authority to regulate carbon dioxide, it could choose not to do so for other reasons, like the uncertainty of the science or questions over available technologies.

Only Judge David S. Tatel said the law was clear that the agency was required to regulate emissions when public health and climate considerations were at issue. Beyond its effect on federal policy, the case holds important implications for California and 10 other states that have assumed that the Clean Air Act authorizes regulations for carbon dioxide and other gases and have adopted their own stringent limits for automobile and truck emissions. The state laws, scheduled to go into effect for the 2009 model year, have been challenged in court by automakers.

A ruling by the Supreme Court could influence another case currently before the same appeals court, involving many of the same plaintiffs. They are arguing that the E.P.A. should also regulate carbon emissions from power plants. A spokeswoman for the E.P.A., Jennifer Wood, said the agency had made the right decision in refusing to regulate carbon dioxide and defended its advocacy of a voluntary approach to curbing emissions.

"The presidents policy achieves near-term reductions while investing in long-term solutions," Ms. Wood said in a statement. "In 2004, E.P.A.s voluntary partnerships prevented over 60 million metric tons of greenhouse gas emissions, equivalent to the annual emissions from over 40 million vehicles." David Bookbinder, a senior lawyer for the Sierra Club, said the Supreme Courts willingness to hear the case reflected the urgency of the issue. "It clearly indicates that they are acknowledging the importance of climate change as a public policy matter," Mr. Bookbinder said.
(Por Michael Janofsky, , The NY Times, 27/06/2006)