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The Double Edge of Density: Local Pollution
Photo by Dr. Keats.

Photo by Dr. Keats.

The environmental movement is, rightfully, focused almost entirely on greenhouse gas emissions right now. That is almost certainly strategically correct, given the stakes. It’s important to remember, though, that there lots of kinds of pollution out there that aren’t GHG emissions that we also need to be keeping an eye on. For example, a recent study found that prenatal exposure to urban air pollution significantly decreases children’s IQ. I’m not qualified to comment on the science of the study, nor do I want to give too much credence to IQ tests in general, but it’s an important reminder of the importance of local emissions.

It also complicates what is normally the easiest solution to environmental issues, simply increasing density in our urban areas. It’s nearly always the case that the reduced carbon emissions from decreased commuter VMT, from efficiencies in heating and cooling, and from more centralized economic activity mean that density leads to fewer emissions, per capita. There’s a wonderful New Yorker article from a few years back that goes through this all in the (sui generis) case of Manhattan.

Per capita, though, isn’t always the best way of looking at environmental problems.

Per capita numbers show efficiency; they tell us how much a certain technology or lifestyle pollutes. It’s usually the right way of evaluating a given choice as more or less green. Per capita does not, however, look at effects. The atmosphere, for example, does not care about per capita emissions. It cares about total emissions.

In the case of the particulate pollution that the IQ article talks about, the relevant number is the total but roughly the total per square mile. The suburbs might have much higher particulate emissions per capita—those trucks have to drive many more miles to get to the suburban supermarket—but by diffusing it over a larger area the health and ecosystem effects of that pollution are mitigated. It’s precisely this kind of pollution that makes people feel like suburbs are clean and green rather than dirty.

This isn’t a call for us all to move out to the suburbs, fleeing air pollution. It is a reminder that it is not enough to simply call for more density. D.C. already has some of the worst air pollution in the country. Increasing density must happen, but it is non-negotiable that increasing density be paired with mechanisms to improve local air quality.

Luckily, there are many such programs. D.C. has an anti-idling law that I’m quite sure could be better enforced. Anything that increases the speed and efficiency of our bus fleet would decrease local air pollution, even beyond the fuel improvements that WMATA has made. More broadly, efforts to get people on transit, on bicycles, and walking need to be strengthened.

The District is the kind of place that is doing very well on emissions, per capita. We need not to be have our environmental efficiency punished with high densities of local pollution.

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  • Noah Kazis

    Kaid, thanks for the, as always, great thoughts.

    I’d just clarify that per capita is always the right way to look at solutions, but often the wrong way to analyze problems. The problem that will hurt us is that there is too much carbon in our atmosphere, not that we each produce too much carbon. The solution is to reduce our per capita carbon consumption.

  • While I agree with the conclusion in your post – we must indeed mitigate the local effects of density – I have to take minor issue with a couple of its premises. First, we in the environmental community are not “focused almost entirely” on carbon emissions, though many of us at the national level are. At the local level, I think it is much less common, with issues like water quality, natural resource protection, and air quality frequently taking precedence. And those are the top issues for some important national groups as well.

    Second, I think it is absolutely critical that we think in terms of per capita impacts, especially given that the US will grow by 50% or so in population over the next half-century. We can’t possibly get the total emissions down to a manageable level without working on per capita emissions. And that goes for other environmental issues, too – we need to plan growth with reduced per capita water runoff, land consumption, and the like if the planet is going to have a chance. I wrote a post about this on my own blog last year. It has taken almost the entirety of my 30-year environmental career to see our movement finally, finally get how important that is.

    All that said, I do agree with your conclusion. No one argues for density more than I do, but it is important that we not do so with blinders on. We need lots of mitigation measures (think green roofs and porous pavement to help with urban runoff). And I also think we need to consider the humanity of density (locally, for instance, I hate the concrete canyons of Ballston and Rosslyn). I’m in favor of moderately increased density, and variable density, not uniformly high density, for a lot of places here and elsewhere.

    Loved the David Owens article in the New Yorker when it came out, BTW He soon will have a book expanding on the thesis, if he doesn’t already.