It is not just the state of California that is bypassing the authority of the US government to take action on global warming.
The mayors of more than 300 cities across the country have signed a Climate Protection Agreement in which they have pledged to meet the emissions-cutting timetable laid down by the Kyoto Protocol - regardless of what the Bush administration decides.
Some of those cities, such as Seattle, which took the lead on drafting and lobbying for the agreement, are bastions of liberal politics and environmentalism, acting out their ideological convictions. Others, though, such as the exclusive Colorado ski resorts Vail and Aspen, are also motivated by a powerful self-interest. If global warming continues unabated, the Rocky Mountain snowpack will melt and there will be no skiing in Vail, Aspen or anywhere else by the end of this century.
Seattle's Mayor, Greg Nickels, proposed the mayors' agreement whenKyoto came into effect at the start of last year. By June 2005, he had 140 signatories, and the number has more than doubled since.
The goal is to "meet or exceed" the Kyoto target of cutting global warming pollution to 7 per cent below 1990 levels by 2012.
The agreement also contains a 12-point action plan, urging signatory cities to discourage sprawl, promote public transport, car-pooling and bicycle lanes, turn to alternative energy sources including alternative fuels for the municipal vehicle and bus fleet, plant lots of trees and introduce environmental education programmes in schools and community colleges.
Seattle, in the Pacific Northwest, is the perfect poster-child for many of these initiatives, since it sits between two heavily forested mountain ranges and is surrounded by water. Despite a long history of environmentalism and commitment to public transport, it has been struggling with smog problems in recent years because of heavy car commuter traffic from the ever-expanding suburbs.
The Colorado ski resorts, meanwhile, have taken robust action to convert to renewable energy to power their ski lifts, shops, hotels and administrative buildings.
Vail just signed a deal to buy more than 150,000 megawatt-hours of wind power per year - the greenhouse gas-saving equivalent of taking 18,000 cars off the roads. Aspen, meanwhile, commissioned a study in April that revealed the severe damage done to the environment by private jets landing at its airport. It is now working to curtail air traffic.
Aspen's top city lawyer, John Worcester, described the city earlier this year as the global-warming equivalent of "the canary in the miner's cage". "It is incumbent on all of us," he said, "to face the potential threat upon our economy and way of life as we would any other potential threat".