Scientists on the Intergovernmental Panel on Climate Change (IPCC) of the United Nations, meeting in Valencia one month ago, advised that global temperatures are increasing because human beings emit too much carbon dioxide and other greenhouse gases (carbon). The economic theories suggest that when something is taxed, it reduces in quantity. Therefore, if we want to reduce global emissions of carbon, we need a global tax system for these emissions to the atmosphere. The document produced in Valencia (Summary of Policymakers of the Synthesis Report of the IPCC Fourth Assessment Report) advises, among other instruments of environmental policy, that taxation as a tool to fight against climate change is appropriate.

When I was preparing this week’s class of microeconomics, which is dedicated to Externalities, I found an interesting article by Gregory Mankiw titled One Answer to Global Warming: A New Tax , published in The New York Times. It argues that a global tax for the emission of carbon dioxide and other greenhouse gases would be easier to negotiate than the rights of emissions arising with the Kyoto agreement.

The idea of using taxes to fix problems, rather than merely raise government revenue, has a long history. The British economist Arthur Pigou advocated such corrective taxes to deal with pollution in the early 20th century. In his honor, economics textbooks now call them ”Pigovian taxes.” Using a Pigovian tax to address global warming is also an old idea. It was proposed as far back as 1992 by Martin S. Feldstein on the editorial page of The Wall Street Journal. Once chief economist to Ronald Reagan, Mr. Feldstein has devoted much of his career to studying how high tax rates distort incentives and impede economic growth. But like most other policy wonks, he appreciates that some taxes align private incentives with social costs and move us toward better outcomes.

Those vying for elected office, however, are reluctant to sign on to this agenda. Their political consultants are no fans of taxes, Pigovian or otherwise. Republican consultants advise using the word ”tax” only if followed immediately by the word ”cut.” Democratic consultants recommend the word ”tax” be followed by ”on the rich.” Yet this natural aversion to carbon taxes can be overcome if the revenue from the tax is used to reduce other taxes. By itself, a carbon tax would raise the tax burden on anyone who drives a car or uses electricity produced with fossil fuels, which means just about everybody. Some might fear this would be particularly hard on the poor and middle class.

But Gilbert Metcalf, a professor of economics at Tufts, has shown how revenue from a carbon tax could be used to reduce payroll taxes in a way that would leave the distribution of total tax burden approximately unchanged. He proposes a tax of $15 per metric ton of carbon dioxide, together with a rebate of the federal payroll tax on the first $3,660 of earnings for each worker.

A carbon tax would provide incentives for people to use less fuel in a multitude of ways. Any long-term approach to global climate change will have to deal with the emerging economies of China and India. By some reports, China is now the world’s leading emitter of carbon, in large part simply because it has so many people. The failure of the Kyoto treaty to include these emerging economies is one reason that, in 1997, the United States Senate passed a resolution rejecting the Kyoto approach by a vote of 95 to zero.

A global carbon tax would be easier to negotiate. All governments require revenue for public purposes. The world’s nations could agree to use a carbon tax as one instrument to raise some of that revenue. No money needs to change hands across national borders. Each government could keep the revenue from its tax and use it to finance spending or whatever form of tax relief it considered best.

Convincing China of the virtues of a carbon tax, however, may prove to be the easy part. The first and more difficult step is to convince American voters, and therefore political consultants, that ”tax” is not a four-letter word. (Source: “One Answer to Global Warming: A New Tax”. By N. GREGORY MANKIW. Published: September 16, 2007).