New study maps carbon footprints, comes to surprising conclusions


One could lose oneself for hours in the patterns and erratic splotches of colors. Do I live in a swath of self-righteous green? Or in guilt-ridden, fiery orange? Does urban density really reduce our environmental impact? And how gluttonous are those McMansion-dwelling exurbanites, anyway?

The answers to all these questions and more are now just a mouse-click away thanks to an exhaustive household carbon footprint study, complete with those colorful and hypnotic interactive maps, recently published by University of California Berkeley researchers. Drawing on all sorts of data, from the amount of time folks spend in their cars to the number of rooms in their homes to the sources of energy that power their homes, they were able to determine how much greenhouse gases the average household in a particular geographical area is spewing into the atmosphere. The more you consume, the bigger your carbon footprint.

At first glance, the findings aren't so surprising: If you live in a very densely populated urban area — say San Francisco proper or even downtown Los Angeles — your household carbon footprint is likely to be lower than just about anyone else’s. That’s because city-dwellers live in smaller homes, don’t have to travel as far to get to work or run errands, and are more prone to walking or riding public transport than they are to hop in their car and drive. Meanwhile, the California city folk have a relatively low energy-related carbon footprint because California’s electricity mix leans more on hydropower, solar and wind, and less on coal, than other parts of the country.

Yet there is also a bit of a twist. Earlier studies had found a direct, negative correlation between density and carbon footprints — that is, emissions decrease as population density increases. Christopher Jones and Daniel Kammen, the Berkeley researchers, however, “reveal a more nuanced relationship between population density and HCF.” The suburbs just outside those green cities, it turns out, are colored a deep orange on the maps, signifying an unusually large carbon footprint, whether they are densely populated or not. Indeed, the suburban emissions "shadow" tends to blot out the efficiencies of the urban core, making the per capita carbon footprint of big metro areas just as big or bigger than those of smaller, sprawling cities or rural areas.

“As a policy measure to reduce GHG emissions,” Kammen and Jones write, “increasing population density appears to have severe limitations and unexpected trade-offs. In suburbs, we find more population dense suburbs actually have noticeably higher HCF, largely because of income effects.” Yes, income effects: Rich people have bigger carbon footprints, mainly because they live in bigger houses, have more cars and generally consume more of everything.

As one might expect, most of the extra suburban emissions come from transportation. America’s suburbs, especially those in the West, were designed and built with the automobile in mind, making residents prisoners of their cars. Walking or biking from one’s cul-de-sac to work in the urban core can be a harrowing experience, and in some places virtually impossible. Even when progressive metros like Denver expand the public transit web out into the ‘burbs, it’s not always easy to get from home to the bus stop without driving, and if you’re driving to the bus stop, why not just keep going all the way to work?

A cruise around the average-miles-driven map of the Denver area reveals this phenomenon. Folks in downtown Denver drive, on average, around 700 to 800 miles per month, while Denver-fringe suburbanites and exurbanites drive between 2,000 and 3,000 miles per month. The farther they live from the urban core, the farther they drive. Meanwhile, in my hometown of Durango, down in the southwestern corner of the state, commutes are decidedly shorter. Yet we still put 1,800 miles on our cars every month, on average. By my reckoning, 1,500 of those miles are to go skiing or to get to the mountain biking or hiking trailheads.

So what’s the takeaway, aside from the ability of those of us in the green zones to thumb our noses at those who live in the orange and red zones? It’s that dealing with carbon emissions is a complex, place-specific battle. We can’t simply shut down the coal power plants (doing so would have little effect these days on most of California’s carbon footprint); we can’t just use land-use regulations to increase population density; and we can’t just make cars more efficient. We need to do all of the above, and then some. We must figure out how to get suburbanites out of their cars and make their big homes more efficient, along with putting solar panels on the roofs. Urban areas need to get their food from farms that are closer to homes (food makes up a large share of city emissions). Mostly, we need to change the way we, as individuals, behave.

“… 80 percent GHG reductions are possible only with near technical potential efficiencies in transportation, buildings, industry and agriculture,” write Jones and Kammen. “To the extent that these efficiencies aren’t met, highly tailored behavior-based programs must make up the difference.”

Jonathan Thompson is a senior editor at High Country News. He tweets @jonnypeace.

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