My younger son calls the Toyota Prius a "hippie car," and he has a point. Not that Prius drivers are hippies. Toyota says that typical buyers are 54 and have incomes of $99,800; 81 percent are college graduates. But, like hippies, they're making a loud lifestyle statement: We're saving the planet; what are you doing?

This helps explain why the Prius so outsells the rival Honda Civic Hybrid. Both have similar base prices, about $22,000, and fuel economy (Prius, 60 miles per gallon city/51 highway; Civic, 49 mpg city/51 highway). But Prius sales in the first half of 2007 totaled 94,503, nearly equal to all of 2006. Civic sales were only 17,141, up 7.4 percent from 2006. The Prius's advantage is its distinct design, which announces its owners as environmentally virtuous. It's a fashion statement. Meanwhile, the Civic hybrid can't be distinguished by appearance from the polluting, gas-guzzling mob.

The Prius is, I think, a parable for the broader politics of global warming. Prius politics is mostly about showing off, not curbing greenhouse-gas emissions. Politicians pander to "green" constituents who want to feel good about themselves. Grandiose goals are declared. But measures to achieve them are deferred—or don't exist.

California Gov. Arnold Schwarzenegger is the champ of Prius politics, having declared that his state will cut greenhouse emissions to 1990 levels by 2020 (about 25 percent below today's levels) and is aiming for an 80 percent reduction below 1990 levels by 2050. However, the policies to reach these goals haven't yet been formulated; that task has been left to the California Air Resources Board. Many mandates wouldn't take effect until 2012, presumably after Schwarzenegger has left office. As for the 2050 goal, it's like his movies: make-believe. Barring big technological breakthroughs, the chances of reaching it are zero.

But it's respectable make-believe. Schwarzenegger made the covers of Time and NEWSWEEK. The press laps this up; "green" is the new "yellow journalism," says media critic Jack Shafer. Naturally, there's a bandwagon effect. At least 35 states have "climate action plans." None of this will reduce global greenhouse-gas emissions from present levels.

Even if California achieved its 2020 goal (dubious) and the United States followed (more dubious), population and economic growth elsewhere would overwhelm any emission cuts. In 2050, global population is expected to hit 9.4 billion, up about 40 percent from today. At modest growth rates, the world economy will triple by midcentury.