Published online on May 18, 2011, in Nature.

The United States has abandoned comprehensive greenhouse-gas curbs, but California is pressing ahead. Mary Nichols is leading the fight against emissions.

Mary Nichols can take some pride in the view as she travels out of Los Angeles. The San Gabriel Mountains rise up to the north, framed by blue sky with just a touch of midday haze. The clear vista comes in large part because of the California Air Resources Board (CARB), the agency that Nichols leads, which has spent decades cleaning up the city’s air. Now she and her team are setting their sights even higher — with an ambitious plan to cut California’s greenhouse-gas emissions.

With an economy that outranks all but eight countries, California is a political and economic heavyweight that has never been afraid to flex its muscles. It is big enough make an impact, and now that politicians in Washington DC have abandoned attempts to enact a national climate law, California is forging ahead on its own. Nichols feels the burden of that strategy acutely, and she is well aware of the challenges ahead.

In the run-up to the state elections last November, many feared that Californian voters would follow Washington DC’s lead and cast aside the state’s landmark climate legislation, AB 32. The 2006 law requires a 10% reduction in greenhouse-gas emissions by 2020, and critics — fuelled in part by donations from the fossil-fuel industry — argued that the state’s economy was too fragile to withstand aggressive new regulations. But voters turned out en masse to preserve the initiative, which is the first comprehensive climate programme in the United States. California has committed to reducing emissions by the same percentage as the European Union, and the state’s unique plan could chart new ground internationally.

Since the 1970s, California has pushed the boundaries of environmental regulation, acting out of both pride and self-preservation. The state has pioneered environmental laws targeting air pollution, water contamination and toxic chemicals. It has advanced the sciences of atmospheric physics and chemistry, developed pollution-control technologies and bullied powerful industries into submission in an epic battle against choking smog in the Los Angeles basin. Other states, and eventually the nation, have followed California’s path in developing regulations to control pollution.

But Nichols and her staff at CARB need to go even further to rein in greenhouse-gas emissions. The agency plans to clean up vehicle fuels, promote renewable energy and squeeze more reductions by improving energy efficiency. It is also designing the world’s most comprehensive carbon market, set to launch at the start of 2012. Nichols believes that California will one day be able to demonstrate to the rest of the country how environmental protection and economic growth can coexist.

“People in this state are bullish on the ability of California to survive and change, and they fundamentally care about air pollution and environmental issues,” says Nichols. “What we do here matters.”

From Washington DC to Brussels and Beijing, government leaders will monitor the state’s progress closely. Henry Derwent, president of the International Emissions Trading Association based in Geneva, Switzerland, says that California’s plans are reassuring governments around the world that all is not lost in the United States. “The overriding feeling in Europe at the government level is relief,” says Derwent. “Even though it’s not the entire United States, it’s a pretty big consolation prize.”

To continue reading, visit Nature.