I’m a supporter of a cap-and-trade system over a carbon tax. But I have to say that Terry Dinan, of CBO’s Microeconomic Studies Division, has the best argument in favor of a carbon tax over cap-and-trade that I’ve yet seen. (Her paper is here; the CBO director’s blog entry on the subject is here.)
Analysts generally conclude that a tax would be a more efficient method of
reducing CO2 emissions than an inflexible cap. The efficiency advantage of a tax stems from the contrast between
the long-term cumulative nature of climate change and
the short-term sensitivity of the cost of emission reductions. Climate change results from the buildup of CO2 in
the atmosphere over several decades; emissions in any
given year are only a small portion of that total. As a
result, limiting climate change would require making
substantial reductions in those emissions over many
years, but ensuring that any particular limit was met in
any particular year would result in little, if any, additional
benefit (avoided damage). In contrast, the cost of cutting
emissions by a particular amount in a given year could
vary significantly depending on a host of factors, including the weather, disruptions in energy markets, the level
of economic activity, and the availability of new low-carbon technologies (such as improvements in wind-power technology).
Relative to a cap-and-trade program with prespecified
emission limits each year, a steadily rising tax could better
accommodate cost fluctuations while simultaneously
achieving a long-term target for emissions. Such a tax
would provide firms with an incentive to undertake more
emission reductions when the cost of doing so was relatively low and allow them to reduce emissions less when
the cost of doing so was particularly high. In contrast, an
inflexible cap-and-trade program would require that
annual caps were met regardless of the cost, thereby
failing to take advantage of low-cost opportunities to cut
more emissions than were required by the cap and failing
to provide firms with leeway in years when costs were
higher.
The efficiency advantage of a tax over an inflexible cap
depends on how likely it is that actual costs will differ
from what policymakers anticipated when they set the
level of the cap. Given the uncertainties involved, such
differences are likely to be large–and, therefore, analysts
generally conclude that the efficiency advantage of a tax is
likely to be quite large. Specifically, available research
suggests that in the near term, the net benefits (benefits
minus costs) of a tax could be roughly five times greater
than the net benefits of an inflexible cap. Put another
way, a given long-term emission-reduction target could
be met by a tax at a fraction of the cost of an inflexible
cap-and-trade program.
As I say, this is a good argument. But it’s also a bit weird: in my mind, the whole point of using a cap-and-trade system rather than a carbon tax is that no one knows what the actual costs of carbon emissions reduction are going to be. If those costs turn out to be much higher than anticipated, a carbon tax will simply fail, since it will have been set too low. A cap-and-trade system, by contrast, is dynamic: it can be adjusted in real time to reflect new information about the costs and benefits of certain levels of carbon emissions.
Dinan’s arguments do mitigate in favor of some flexibility in a cap-and-trade system, perhaps by being able to borrow or bank future carbon credits. And if they persuade the US government to implement a carbon tax, that would be wonderful: while I’m a supporter of cap-and-trade, a carbon tax is very nearly as good, and much better than the most likely outcome, which is nothing at all.