AP/AFP

CALIFORNIA is America's most populous state and, if independent, would boast the world's eighth-biggest economy. It is also often seen as a trailblazer, both within America and beyond. So on August 31st, when California's lawmakers approved a measure to cut emissions of the gases that cause global warming, the decision reverberated far beyond the state's borders.

America has long been a laggard in the fight against global warming. Soon after becoming president in 2001, George Bush renounced the Kyoto Protocol, a treaty backed by the United Nations that aims to reduce emissions of the offending greenhouse gases. Seven north-eastern states are setting up a system to cap and then reduce emissions of carbon dioxide, the main greenhouse gas, from power stations. But before California's move, no American state had a broad mandatory scheme, of the kind currently operating within the European Union.

Californians have plenty of reasons to fear global warming. Already, snow is melting earlier in the year in its mountains, causing problems not only for skiers but also for the farmers who rely on steady supplies of melt-water to irrigate their crops. Some scientists foresee more droughts and forest fires, and higher, stormier and more acidic seas along California's long coastline. The state's voters are a green lot and their representatives have led the country in tightening restrictions on all manner of pollutants, including greenhouse gases. In 2002, for example, they passed a law that calls for a gradual reduction in carbon-dioxide emissions from vehicles.

The new law requires a similar phased reduction in emissions from big industrial polluters starting in 2012. Firms will have to cut their own emissions, or buy the rights to cuts made by other firms. By 2020 emissions should be back to the level of 1990—a less exacting target and timetable than that demanded by the Kyoto Protocol. The politicians are leaving all the details, including who will do the cutting, how the trading mechanism will work and what the penalties for failure will be, up to the agency that enforces the state's existing air-pollution standards. Business lobbyists, who argue that the law will simply prompt gas-belching industries to relocate to more accommodating jurisdictions, and so cost the state jobs and tax revenue, will almost certainly challenge it in court—as they have the law on vehicles.

Even if the law succeeds in reducing emissions as planned, however, it will have little practical effect on global warming. California, after all, only accounts for about 2% of the world's output of greenhouse gases. The rest of America, and other big sources of emissions, such as China, will remain free to pollute as they please. But the law's supporters argue that other places will inevitably regulate greenhouse gases as global warming begins to bite and that Californian businesses will benefit from being in the vanguard of this trend.

California's politicians certainly hope to benefit from being ahead of the crowd. They rushed the law through ahead of November's elections, doubtless in order to campaign on their green credentials. Arnold Schwarzenegger, California's governor, who is up for re-election this year, backed the measure despite objections from his fellow Republicans, presumably in the hopes of appealing to the state's largely Democratic electorate.

Meanwhile, Mr Bush, another embattled Republican, continues to insist that he opposes mandatory emissions-reduction schemes. But pundits are beginning to wonder whether the same logic that appealed to Mr Schwarzenegger might also convince him. How better to distract attention from other thornier issues and steal some of the Democrats' thunder than by unveiling a big environmental initiative?