Earth Protect Blog

Climate change is helped along by suburban driving culture. We need to embrace cities -- and walking 

Excerpted from "Walkable City: How Downtown Can Save America, One Step at a Time"

In 2001, Scott Bernstein, at the Center for Neighborhood Technology in inner-city Chicago, produced a set of maps that are still changing the way we think about our country. In these maps, remarkably, the red and the green switched places. This reversal, perhaps even more than the health discussion, threatens to make walkability relevant again.

By red and green, I am referring to carbon emissions. On typical carbon maps, areas with the greatest amount of carbon output are shown in bright red, and those with the least are shown in green, with areas in between shown in orange and yellow. Basically, the hotter the color, the greater the contribution to climate change.

Historically, these maps had always looked like the night-sky satellite photos of the United States: hot around the cities, cooler in the suburbs, and coolest in the country. Wherever there are lots of people, there is lots of pollution. A typical carbon map, such as that produced in 2002 by the Vulcan Project at Purdue University, sends a very clear signal: countryside good, cities bad.

For a long time, these were the only maps of this type, and there is certainly a logic in looking at pollution from a location-by-location perspective. But this logic was based on an unconsidered assumption, which is that the most meaningful way to measure carbon is by the square mile. It isn’t.

The best way to measure carbon is per person. Places should be judged not by how much carbon they emit, but by how much carbon they cause us to emit. There are only so many people in the United States at any given time, and they can be encouraged to live where they have the smallest environmental footprint. That place turns out to be the city — the denser the better.

For this reason, when Bernstein replaced carbon per square mile with carbon per household, the colors simply flipped. Now the hottest areas in each American metropolitan area — and their web site shows hundreds, from Abilene to Yuma — are inevitably the outer suburbs. The coolest are smack-dab in the center of town.

To be accurate: Bernstein’s maps have a limitation. They do not show full carbon output; they only show CO2 from household automotive use — data that are much easier to collect. But this limitation turns out to be useful, for several reasons: first, because it causes us to confirm that automobile use is not only the single greatest contributor to our total carbon footprint, but also a reliable indicator of that total; and second, because limiting our greenhouse gas emissions, for many, is a much less pressing issue than our dependence on foreign oil.

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By Jeff Speck