I refuse to give up on a carbon tax. In a new column for National Journal (the link expires at the end of next week), I explain why, and criticize the approaches of both Obama and McCain to energy policy.

Much the most important part of [their] programs is the seemingly brave commitment both have made to a long-term cap-and-trade regime for control of carbon. This could indeed be, to use Al Gore's favorite word, a "transformative" undertaking. Obama sets a goal to reduce carbon emissions to 80 percent below 1990 levels by 2050. McCain's goal is a bit less ambitious--a cut to 60 percent below the 1990 benchmark by 2050. Both are promising, in effect, a wholesale restructuring of the U.S. economy around the goal of carbon abatement.

Let us assume this is desirable. Do they mean it? Do they understand what these commitments entail? (If they do, they certainly aren't spelling it out to voters.) Is there any chance that either goal will be met?

You have to wonder. The country's mood on global warming has changed--most people now seem to take the danger seriously--but public opinion on energy policy has two contradictory strands. People are worried about rising temperatures and changing climate; but they are also worried about expensive gas. If you are serious about reducing carbon emissions, expensive gas is not a problem; it is an unavoidable part of the solution.

Politicians of both parties take it for granted that the American voter cannot tolerate an explicit tax on carbon, which would be the best way to curb greenhouse gases. This supposedly immovable resistance is why the presidential candidates advocate a system of tradable emission permits instead. But if cap-and-trade binds tightly enough to make a difference, it will necessarily make carbon-releasing fuels more expensive. The system cannot work any other way: It can succeed only by attaching an implicit tax to carbon.

Do Obama and McCain think voters are too stupid to see this? When fuel gets more expensive, won't voters object just as strenuously as they would have if a carbon tax had been imposed in the first place? You cannot hope to transform the economy and have nobody notice--can you?

And another thing: In setting their bold targets for 2050, Obama and McCain know they will not be held accountable for failing to meet them. Any such failure is 42 years away and somebody else's problem. Politically, their best bet may be to take credit for seeming to confront the problem while deferring real action and its unpopular consequences another four or eight years.

Europe's politicians have already worked out their own way of seeming bold on climate change while actually doing nothing: It is called the Kyoto Protocol. America's promised cap-and-trade system could easily go the same way. Willingness to advocate an explicit carbon tax--or at any rate, to spell out the equivalent consequences of a binding cap-and-trade system--is the real test of whether either candidate is ready to confront this issue. So far, both are failing that test.