US Supreme Court forces EPA emissions rethink

he US Supreme Court ruled on Monday that the Environmental Protection Agency's refusal to regulate greenhouse gas emissions from cars is "not in accordance with law".

The ruling, which was a defeat for president George W. Bush's administration, marks the first high court decision in a case involving global warming. The case was narrowly decided, by a majority of five to four.

The decision was a victory for the 12 states and 13 environmental groups that had sued the Environmental Protection Agency (EPA) arguing that the Clean Air Act gives the agency the authority to regulate CO₂ and other greenhouse gases emitted from cars. The federal government had insisted that the EPA did not have that authority.

The nation's highest court said the EPA "has offered no reasoned explanation" for its refusal to regulate CO₂ and other vehicle emissions that contribute to climate change.

This is one of the most prominent environmental cases to reach the Supreme Court in decades. It revolves around the US Clean Air Act's statement that the head of the EPA "shall" regulate emissions of new vehicles "which in his judgment cause, or contribute to, air pollution which may reasonably be anticipated to endanger the public health or welfare".

The EPA has declined to regulate greenhouse gases from cars under the statute, citing scientific uncertainty. It has also claimed that if Congress had intended for that part of the Clean Air Act to apply to greenhouse gases, it would have said so explicitly when it last amended the act in 1990.

Arbitrary and capricious

Justice John Stevens rejected the administration's argument that the EPA lacked the power to regulate such emissions. He said the EPA's decision was "arbitrary, capricious or otherwise not in accordance with law".

Stevens sent the issue back to the EPA for further consideration, saying the Supreme Court would not decide which policy the EPA must follow. "We hold only that EPA must ground its reasons for action or inaction in the statute," he said.

Greenhouse gas emissions have risen steeply over the past century and many scientists see a connection between this rise and an increase in global average temperatures and a related increase in extreme weather, wildfires, melting glaciers and other damage to the environment (see Blame for global warming placed firmly on humankind).

The four justices to vote in favour of the EPA on Monday were the Supreme Court's four most conservative members: Chief Justice John Roberts and Justice Samuel Alito – both appointed by President Bush – and Justices Antonin Scalia and Clarence Thomas.

The case came to the Supreme Court after the US Court of Appeal ruled against Massachusetts in the landmark Massachusetts vs. EPA case (see Climate change: Let the Supreme Court decide).

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