Congress may be thinking about tackling greenhouse-gas emissions, but California has already done it. Its Global Warming Solutions Act, which was passed last year, aims to cut them to 1990 levels by 2020 — an ambitious target for a state that has grown rapidly in the past 15 years and will probably continue to do so. The details have yet to be fleshed out, but the reductions will come from both a cap-and-trade scheme for industry and regulations of various sorts.

Mr Schwarzenegger issued the first such regulation earlier this month, obliging producers of petrol and other fuels to cut the emissions of carbon dioxide from their products by 10% by 2020 — presumably by mixing in more ethanol and other biofuels. It is not California's first attempt to reduce emissions from transport: its legislature voted for stringent cuts in 2002. That move has become snarled in a court battle over whether states have the right to set fuel-economy standards. Meanwhile, the politicians keep trucking. In September, the state showily sued six car manufacturers, alleging they had damaged its climate. It is also suing the EPA, for failing to regulate greenhouse-gas emissions.

California's politicians are keen on renewables too. State law requires utilities to generate 20% of the power they sell from sources such as windmills and biomass plants by 2010, and 33% by 2020. Solar power has won even greater favour: under the "million solar roofs" scheme, the state plans to spend more than $3 billion over the next decade subsidising the installation of solar-power panels.

California has also pioneered the practice of "decoupling", which deprives power firms of their incentive to sell as much electricity as possible. Instead, the local regulator has devised a formula to reward firms whose sales are lower than expected, and to allow the recovery of the costs of energy-efficiency schemes.

Such measures (along with high power prices to pay for them) have helped California rein in its electricity consumption — although lovely weather and a relative lack of heavy industry have also played a part. Power use per person has remained roughly stable in the state since the 1970s, even as it has doubled in the rest of the country (see chart above). As a result, California's greenhouse-gas emissions per person are on a par with those of Denmark. Relative to the size of its economy, they are lower.

But California is not America's only green enclave. Nine states in the north-east have combined to reduce emissions from power generation through a cap-and-trade scheme. Two of them plan to auction all the permits, unlike the countries in the European Union's Emissions Trading Scheme, which handed them out for nothing. Ten states have signed up to follow California's standards on car exhaust, including its requirements on greenhouse gases. Many more promote ethanol, or renewables, or energy-efficient buildings (see chart below).

On the whole, left-leaning states are keener on greenery than right-wing ones, which tend to be more energy-intensive. But politicians of all stripes in the Midwest are keen to promote ethanol for the sake of local farmers, who grow the corn from which it is made. And Texas recently overtook California as the country's biggest generator of wind power.

Greenery is also popular at the local level. Almost 400 cities have devised plans to curb or reduce their greenhouse gas emissions. Many buy only fuel-efficient cars for their municipal fleets. Laura Miller, the mayor of Dallas, has spoken out against the plans of local utilities to build 17 new coal-fired power plants. What is the point of her city buying police cars fuelled by natural gas, she asks, when they will soon be overshadowed by clouds of soot?

Despite all this grassroots environmentalism, America remains the biggest contributor to global warming, accounting for roughly a fifth of all the world's emissions. The federal government's recalcitrance on the subject remains the biggest obstacle to an effective global scheme to tackle the problem. But whereas in Europe or Asia new ideas often flow from the centre to the regions, in America the states are the incubators of big shifts in policy. This means that change is coming — fast.

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