With President George W. Bush and his administration continuing to avoid the issue, the courts and Congress are poised to shape climate-change policy in the United States.

Last week, the Supreme Court heard a high-profile case in which Massachusetts, along with numerous other states, cities and environmental groups, argued that the Environmental Protection Agency (EPA) should be forced to regulate greenhouse-gas emissions from cars and trucks as a pollutant. Massachusetts itself stands to lose 300 kilometres of its coastline as a result of the rise in sea level as the planet warms.

The suit can be read as an expression of many states' impatience with the federal government's inaction on climate change (see Nature 443, 486–487; 2006). Meanwhile, staff in the offices of Democratic politicians are sharpening their pencils for January, when the more liberal party takes over Congress, and supporters hope that climate-change bills will fly.

The verdict will be announced by the Supreme Court by the end of its term in June. Although the EPA trotted out the same old administration line that the “scientific uncertainty” was too great to act upon, the discussions during the 29 November hearing hint that the case might be decided on the technical grounds of standing — Massachusetts could sue the agency only if the harm suffered will be redressed if the EPA does act. The problem is that climate change is such a large and global problem that the emissions in question — from the tailpipes of US vehicles — may not make a huge difference by themselves. Massachusetts will probably still lose a considerable chunk of coastline.

Beneath the issue of standing, there seems to be a schism of opinion on more ideological grounds, with the more conservative judges looking likely to support the EPA, and the more liberal judges lining up with the Massachusetts group. With four justices on each side, Justice Anthony Kennedy, a noted moderate, may have the casting vote.

But many observers say that the decision itself will be less important than the buzz around the case. “I think no matter which way it breaks, it will put more pressure on Congress,” says Andrew Aulisi of the World Resources Institute, an environmental think-tank in Washington DC. If the Supreme Court sides with the EPA, he says, “everybody is going to throw up their hands and say that the judiciary isn't doing anything and Congress needs to step in”.

When the Democrats take control of Congress in January, the prediction for the first months is a steady diet of hearings, with bills taking a little longer. No one is quite sure if the votes are there for a tough bill on climate change. “What the elections did, to a large extent, was replace Republican moderates with Democratic moderates,” says Manik Roy, director of congressional affairs at the Pew Center on Global Climate Change. “You don't have many more votes. What has changed is who controls the agenda.”

Senator Barbara Boxer (Democrat, California), who will head the Senate Committee on Environment and Public Works, has promised lots of talk and action on climate change, and on 15 November sent a letter with two other heads of related committees to President Bush, asking for a commitment to “pass meaningful climate change legislation in 2007”. Republican Senator (and probable presidential candidate) from Arizona, John McCain, will also undoubtedly reintroduce the McCain–Lieberman Climate Change Act, a cap-and-trade bill, for its third outing.

Frank Maisano, a spokesman for Bracewell & Giuliani, a law firm representing oil and gas industries, cautions that advocates for climate-change regulation have been overtaken by unrealistic exuberance. The complexity of the issue will push substantive action way past the verdict, he says. “It is not something that is going to be slam-dunked in 12 months.”

But even if the rounds of hearings seem to produce nothing but hot air, Roy points out that they will at least educate members of Congress, where, for example, Senator James Inhofe (Republican, Oklahoma) has been holding forth on his view of climate change as some sort of conspiracy theory. “I would not in any way consider it a delay tactic if Congress spends a year holding hearings on this issue,” Roy says.