It’s an old political cliché that we could be witnessing history in the making, but today in the Supreme Court in Washington that might just happen. We might just be witnessing the beginning of the end of the Bush Administration’s flawed and belligerent approach to climate change.

The case, known as Massachusetts v. EPA, has been brought by a dozen states and 13 environmental organizations against the Environmental Protection Agency. They argue that the greenhouse gas emissions from cars, trucks and factories should be regulated by the U.S. government.

They are challenging an appeal court ruling that the Environmental Protection Agency (EPA) – an arm of the administration – was not obliged to regulate CO2. The EPA is defending the action, backed by four motor vehicle trade associations and two coalitions of utility companies and other industries.

At the heart of the case is a dispute over whether greenhouse gases fit the federal Clean Air Act’s definition of a pollutant. The plaintiffs argue that if they do, the EPA then has the power to regulate and cap them. The industry groups argue that it doesn’t, and that carbon dioxide is a naturally occurring gas.

Under the Clinton presidency, the EPA took the line that it did have the authority to regulate CO2. But the Bush administration reversed that policy and, in 2003, the EPA announced that the gas was not a pollutant under the clean air act, and consequently it had no right to regulate it.

When the Supreme court passes judgment sometime next year, it will determine the pace and tone of America’s approach to climate change.

If the states win the action, say campaigners, the EPA would be forced to take a more active approach to controlling emissions. “It would send a powerful signal – not least to the markets – that the US is getting serious, and make real change more inevitable,” said Josh Dorner, a spokesman for the Sierra Club.