The government's fuel economy standards also haven't done much to promote conservation. On average, new vehicles get lower mileage today than they did 20 years ago, thanks to the proliferation of large trucks and SUVs.

The Supreme Court decision precipitated a clamor for stricter mileage rules, which happen to a supremely clumsy answer. The only people immediately affected by higher fuel economy standards are those who buy new vehicles. Other motorists will keep driving their gas-guzzling cars and trucks for years to come, blissfully spared any incentive to conserve. A carbon tax, by contrast, would spur faster progress by raising the cost of driving to everyone.

It also has the advantage of keeping the government role as small as possible. When the government gets directly involved in controlling energy use -- by fiddling with mileage rules, handing out grants and tax incentives, and underwriting particular energy sources -- it invites boondoggles and special-interest gimmicks that benefit politicians without doing much to temper climate change. We'll all be better off if Washington merely levies a tax and gets out of the way, leaving producers and consumers to search out the cheapest means of minimizing emissions.

Of course, no one wants to pay more in taxes. Here's the good news: We don't have to. Some economists propose that carbon tax revenues be used to finance equal cuts in income and payroll taxes. That way, we'd get environmental improvements and a lighter load on companies and workers. Meanwhile, the total tax burden on the economy would be unchanged.

The campaign against global warming promises to be costly and uncomfortable under the best of policies. But if we let it become an excuse for bureaucrats and busybodies to meddle needlessly in our lives, it promises to be even worse, for us and the planet.