In a New York Times column, Nobel prize winning economist Paul Krugman has written some commentary on the Waxman-Markey legislation that proposes to introduce an emissions trading scheme in the United States. It is well worth reading. In his column, when Krugman discusses some of the objections to the scheme, he states:

One objection — the claim that carbon taxes are better than cap and trade — is, in my view, just wrong. In principle, emission taxes and tradable emission permits are equally effective at limiting pollution. In practice, cap and trade has some major advantages, especially for achieving effective international cooperation.

Not to put too fine a point on it, think about how hard it would be to verify whether China was really implementing a promise to tax carbon emissions, as opposed to letting factory owners with the right connections off the hook. By contrast, it would be fairly easy to determine whether China was holding its total emissions below agreed-upon levels.

I agree with Krugman that cap and trade has major advantages in terms of achieving international cooperation. This is the main reason why I support cap and trade. However, because carbon dioxide is more or less a stock pollutant, it has been argued that setting a price by introducing a carbon tax will be more likely to reduce emissions by an appropriate amount. I therefore disagree with Krugman that setting a tax is equivalent in principle to having tradable permits, because of uncertainty.

A cap and trade system with a price floor has the same advantages to emissions trading when it comes to international cooperation; it also has the same advantages of carbon taxation (and is probably superior to carbon taxation) when it comes to managing uncertainty. Unfortunately,it is very to find a serious discussion about price floors in the peer-reviewed economic literature since 1976 (but Roberts, M. J., Spence, M., 1976, ‘Effluent Charges and Licenses under Uncertainty’ is well worth reading). Most of the discussion on hybrids between cap-and-trade and carbon taxes has been about schemes with price ceilings.

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Update: The Waxman-Markey bill does in fact have a price floor.

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