California’s newly released regulatory initiative to reduce greenhouse gas emissions from new cars sold in that state represents the triumph of symbolism over substance. It’s an ill-considered gesture that ought to annoy partisans on both sides of the global warming fence.

How much will these new emission rules help in the fight against global warming? “Not much” would be a charitable answer.

Back-of-the envelope calculations derived from computer simulations performed by climatologist Tom Wigley (who, by the way, supports aggressive action to address the threat of global warming) suggest that even if every state in the union adopted California’s new program, global temperatures would drop by something less (actually, probably far less) than one-tenth of 1 degree Fahrenheit by 2050. What everyone in the scientific community understands but few want to discuss publicly is that stopping global warming — or even slowing it down appreciably — requires the near total abandonment of fossil fuels.

Suggesting otherwise only encourages the public to believe that they can meaningfully address climate change without sacrifice.

Because I’m against economic sacrifice, that’s fine with me. While the planet is indeed warming — probably due in no small part to industrial greenhouse gas emissions — the warming has been modest, benign, and largely confined to northern latitudes during winter nights. There are good reasons to expect that warming pattern to continue. And that warming pattern does not threaten to usher in the convulsive climatic events we are warned about in the press or in the movie theaters. In fact, some scientists and economists can make a pretty good case that global warming will prove a net plus to both the economy and the global environment.

So perhaps I should applaud California’s regulations. Unfortunately, this empty gesture isn’t completely cost-free.

The California Air Resources Board estimates that their plan will add about $1,000 to the cost of a new car by 2015. Question: How many people would be willing to pay a $1,000 tax each time they buy a new car to reduce global temperatures 46 years from now by a number too small to measure? How many economists could you find who’d accept that such a tax passes any sane cost-benefit test? Not many, I’ll bet.

When pressed on this, environmentalists counter that anything that begins the long regulatory journey they envision before us is valuable in and of itself. But if the first baby steps necessary to initiate this journey are so expensive and so obviously incapable of passing any reasonable cost-benefit test, how expensive do you think future steps might be that environmentalists dare not forward at the moment?

Then there are the hidden costs. Because there are no technologies available to remove greenhouse gas emissions from automobile tailpipes, the only way to comply with the California mandate is to improve auto fuel efficiency. Yet improving fuel efficiency reduces the marginal cost of driving one’s car, and economists have demonstrated that people respond to those lower driving costs by actually driving more.

What does more driving mean? More pollution, that’s what. Economist Andrew Kleit of Pennsylvania State University calculates that a 50 percent increase in the fuel efficiency of the automobile fleet — essentially what California is requiring through these regulations — will increase net automobile emissions of volatile organic compounds by 1.9 percent, nitrogen oxides by 3.4 percent, and carbon monoxide by 4.6 percent. In other words, environmentalists are asking us to trade off an infinitesimal reduction in global temperature for more smog than we might experience otherwise.

This wouldn’t be the case if environmentalists were more honest with the public about the costs associated with their policy prescriptions. The fact is that the only way to reduce greenhouse gas emissions is to increase the cost of fossil fuels via an implicit or explicit tax. But imposing a fuel tax makes the cost of these policies transparent and, environmentalists fear, difficult to defend politically.

They’re right.