Fun With Only

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Something that kind of bugs me in the policy analysis game is the way that very small terminological choices can do a lot to spin some research. For example, should denser building be part of our strategy for combating climate change? I say yes. Then I see Reihan Salam quote this:

Even if 75 percent of all new and replacement housing in America were built at twice the density of current new developments, and those living in the newly constructed housing drove 25 percent less as a result, CO2 emissions from personal travel would decline nationwide by only 8 to 11 percent by 2050, according to the study. If just 25 percent of housing units were developed at such densities and residents drove only 12 percent less as a result, CO2 emissions would be reduced by less than 2 percent by 2050.

Obviously I can’t evaluate the underlying research, but why is that “only” 8 to 11 percent. Obviously, changing the nature of new construction is going to be somewhat limited in its impact since it won’t have any impact at all on existing structures which will be the large majority of structures for most of the 2009-2050 period. The big appeal of denser building as an emissions-reducer, to me, is that there’s good reason to think that this would be a good idea even absent the climate change issue. Dealing with climate change will require us to do a bunch of stuff that wouldn’t be smart policy if it weren’t the case that CO2 emissions are harmful. But it makes a lot of sense to make sure we do the “dual use” stuff that can improve the quality of our lives in other ways.

At any rate, Reihan comments:

Increasing density is a cause embraced by many environmentalist, including more than a few conservative environmentalists. Yet reducing the weight of personal automobiles might be a more effective strategy.

He follows up with some persuasive evidence that lighter vehicles could do a lot of good. But this obviously isn’t an either/or choice. Indeed, the two policy options have nothing much to do with each other. It seems to me that reducing emissions to an acceptable level is going to require something like a thousand cuts. There’s no sense dismissing particular strategies as “only” cutting a 10 percent chunk out of a given sector. A comprehensive strategy is built out of chunks.