Stavins on cap-and-trade vs. carbon tax

The distinguished Robert Stavins (who is >> Mankiw on cap-and-trade, and probably >>>> Rex Tillerson) takes on the cap-and-trade vs. carbon tax debate.

After first demonstrating the need for a market-based mechanism, he then strongly defends cap-and-trade (and not on the grounds of political pragmatism, which is perhaps the argument most oftenly advanced).

While there are tradeoffs between these two principal market-based instruments targeting CO2 emissions — a cap-and-trade system and a carbon tax – the best (and most likely) approach for the short to medium term in the United States is a cap-and-trade system. I say this based on three criteria: environmental effectiveness, cost effectiveness, and distributional equity. So, my position is not capitulation to politics. On the other hand, sound assessments of environmental effectiveness, cost effectiveness, and distributional equity should surely be made in the real-world political context.

Here is his more detailed argument:

Having said this, there are some real differences between taxes and cap-and-trade that need to be recognized. First, environmental effectiveness: a tax does not guarantee achievement of an emissions target, but it does provides greater certainty regarding costs. This is a fundamental tradeoff. Taxes provide automatic temporal flexibility, which needs to be built into a cap-and-trade system through provision for banking, borrowing, and possibly a cost-containment mechanism. On the other hand, political economy forces strongly point to less severe targets if carbon taxes are used, rather than cap-and-trade – this is not a tradeoff, and this is why environmental NGOs are opposed to the carbon-tax approach.

In principle, both carbon taxes and cap-and-trade can achieve cost-effective reductions, and – depending upon design — the distributional consequences of the two approaches can be the same. But the key difference is that political pressures on a carbon tax system will most likely lead to exemptions of sectors and firms, which reduces environmental effectiveness and drives up costs, as some low-cost emission reduction opportunities are left off the table. But political pressures on a cap-and-trade system lead to different allocations of allowances, which affect distribution, but not environmental effectives, and not cost-effectiveness.

Proponents of carbon taxes worry about the propensity of political processes under a cap-and-trade system to compensate sectors through free allowance allocations, but a carbon tax is sensitive to the same political pressures, and may be expected to succumb in ways that are ultimately more harmful: reducing environmental achievement and driving up costs.

In summary, there is a true trade-off between certainty on emissions reduction and certainty on cost, but in a realistic political environment, the carbon tax is vulnerable to both looser targets, and less efficiency in meeting them. The "picking favorites" criticism directed against legislation such as Waxman-Markey holds equally against a carbon tax, and the political outcomes would be in all likelihood worse from an environmental standpoint.

Update: Environmental Economics highlights a different (but also excellent) passage from Stavins:

The Hamilton Project staff concluded in an overview paper (which I highly recommend) that a well-designed carbon tax and a well-designed cap-and-trade system would have similar economic effects. Hence, they said, the two primary questions to use in deciding between them should be: which is more politically feasible; and which is more likely to be well-designed?

The answer to the first question is obvious; and I have argued here that given real-world political forces, the answer to the second question also favors cap-and-trade. In other words, it is important to identify and design policy that will be “optimal in Washington,” not just from the perspective of Cambridge, New Haven, or Berkeley.

In “policy heaven,” the optimal instrument to address climate-change emissions may well be a carbon tax (largely because of its simplicity), but in the real world in which policy is developed and implemented, cap-and-trade is the best approach if one is serious about addressing the threat of climate change with meaningful, effective, and cost-effective policies.