NEW YORK (AP) Kirk Hammett is one guitar legend who cares about the planet.

"I just said to my wife earlier today this might be the most important moment of our entire career," Hammett told an incredulous interviewer after his band Metallica performed at the London installment of the eight-city Live Earth concert earlier this month. "You know, if we can make that much of a difference, and make that much change, by all means. Because I love the Earth, I love the environment, I love nature. And it's so important."

Can celebrities save the planet? Some of the performers at Live Earth seemed to think they could by converting their tour buses to biodiesel and exhorting their fans to use energy-saving light bulbs such as those made by concert sponsor Royal Phillips Electronics.

"It's amazing! Their slogan is 'It's so simple,' and just one person can use these light bulbs and change the world," marvelled Ashley Roberts, a member of the pop group Pussycat Dolls.

But it isn't really so simple. Preventing catastrophic global warming calls for nothing less than a complete restructuring of the global economy, and buying more efficient light bulbs isn't going to do it.

Individuals can certainly help, but only dramatic action by corporations and especially governments can solve the problem. And the reality is that so far, those institutions have done very little.

In the last year or so the corporate world has increasingly voiced its support for doing something about global warming. This month the Business Roundtable, which represents the chief executives of 160 corporations, called for collective action to reduce greenhouse gas emissions.

Yet many Roundtable members have questionable records when it comes to actually doing anything about the problem. The General Motors brand Chevrolet touted its commitment to the cause with advertisements on the Live Earth web site pointing out that motorists can save gasoline and thus reduce greenhouse gas emissions by keeping their tires properly inflated. If every car in America had properly inflated tires, the ad said, the country would save millions of gallons of gas annually.

That may be. But the United States uses more than 300 million gallons of gasoline per day.

Another spot by Chevy boasted that the company offers eight automobile models that get 30 miles per gallon or better. The spot did not mention that Chevy's best-selling vehicle indeed, the top-selling vehicle in America is a pickup truck with a mileage rating in the teens. Neither did the commercial mention that auto industry lobbyists have blocked significant increases in federal fuel economy standards for decades.

This month, the automakers partially relented by endorsing a House proposal that would increase fuel efficiency to 32 mpg for all new passenger vehicles by 2022.

But Detroit still opposes competing proposals that would boost the standard higher than that. According to the Union of Concerned Scientists, it is possible to build cars, minivans and SUVs that get 40 mpg within a decade using technology that already exists.

Doing that would make a real impact on America's carbon dioxide emissions the equivalent of taking every fifth car off the road. Because cars account for about a quarter of America's carbon dioxide emissions, a 40 mpg fuel economy standard would put a five percent dent in the country's overall production of the gas while reducing the country's reliance on oil. There's a similar story behind those light bulbs. It's true that every person who replaces a traditional incandescent light bulb with one of the new compact fluorescents made by Phillips saves enough energy to prevent about 260 pounds of carbon dioxide from being released into the atmosphere annually.

That's an impressive number, until you consider that the average U.S. household directly produces 12.4 tons of carbon dioxide a year, not counting automotive sources.

To significantly reduce that figure, the nation's utilities are going to have to start generating electricity differently by relying less on coal, which is far and away the most carbon-intensive fossil fuel, and by developing technologies that capture and store the carbon dioxide that is produced when it burns. They are going to have to learn how to generate electricity with solar, wind and other renewable sources. And they may very well have to revive the nation's nuclear industry, which has not built a new plant in three decades thanks to its own constellation of environmental nightmares.

Naturally, some members of the chattering classes accused the Live Earth performers of hypocritically parroting platitudes about an issue they don't really understand or care about. Some critics pointed out that the celebrity lifestyle with its private jets, long limousines and multiple mansions is probably the most environmentally irresponsible way of life on the planet.

"There's been a lot of talk about what's a bunch of rock stars going to be able to do coming in on their private planes and woof, woof, woof," said Simon Le Bon of Duran Duran. "And they're missing the point. The point is this ball's got to get rolling, and it takes a lot of energy to get it started."

A few celebrities really have dedicated themselves to doing something about global warming, both with regard to their own carbon footprints and the globe's.

Leonardo DiCaprio, who arrived at this year's Oscars in a hybrid electric Toyota Prius,produced, co-wrote and narrated "The 11th Hour," a documentary about the state of the global environment that premiered at the Cannes Film Festival in May and is being released later this year.

"We are in the environmental age whether we like it or not," DiCaprio says in the film. "We know the United States, the greatest consumer and source of waste, needs to make a transition to a greener future, but will our pivotal generation create a sustainable world in time? What will guide this massive change?"

When celebrities participate in events like Live Earth, they may raise the awareness of millions, even billions, to the seriousness of global warming. But that awareness matters only if it can be translated into action.

For that the world needs leaders, not entertainers.