Suburban Carbon Footprints Wipe Out City Gains

Households in densely populated cities have carbon footprints that are way smaller than the national average, but there’s a catch: The suburban sprawl that inevitably spills out from big cities offsets the emissions improvements, according to a new study.

And here’s the thing: This connection is so sticky, the researchers see efforts to increase population density as ineffective. Instead, they say the best hope for reducing overall emissions is in promoting low-carbon technologies that are tailored to different locations.

Get out into the Bay Area's suburbs, and emissions intensity increases. (image via UC Berkeley Carbon Maps)

In the Bay Area’s suburbs, emissions intensity increases. (image via UC Berkeley Carbon Maps)

The University of California-Berkeley researchers behind this study used “local census, weather and other data – 37 variables in total – to approximate greenhouse gas emissions resulting from the energy, transportation, food, goods and services consumed by U.S. households, so-called household carbon footprints,” the university said.

They found that while households in big, densely populated cities have a carbon footprint that is on average 50 percent below average, emissions in “households in distant suburbs are up to twice the average,” so the difference between the best performers and worst performers can be a factor of four.

“Metropolitan areas look like carbon footprint hurricanes, with dark green, low-carbon urban cores surrounded by red, high-carbon suburbs,” Christopher Jones, a doctoral student who worked on the research, said in a statement. “Unfortunately, while the most populous metropolitan areas tend to have the lowest carbon footprint centers, they also tend to have the most extensive high carbon footprint suburbs.”

The end result is that “large metropolitan areas have a slightly higher average carbon footprint than smaller metro areas,” the researchers said.

With a tenfold increase in population density in central cities yielding greenhouse gas emissions reductions of just 25 percent, the Berkeley team, led by Professor Daniel Kammen, director of the Renewable and Appropriate Energy Laboratory, said that increasing population density in cities appears to be not worth the effort.

And denser suburbs are even worse than less densely populated ones.

So how to green the ‘burbs? “Suburbs are excellent candidates for a combination of solar photovoltaic systems, electric vehicles and energy-efficient technologies,” Kammen said. “When you package low carbon technologies together you find real financial savings and big social and environmental benefits.”

The researchers have built a cool online tool where you can zoom in to see how the zip code you live in fares on overall carbon footprint as well as emissions per household and for transportation.

The Berkeley study has been published in the journal Environmental Science & Technology.

Pete Danko is a writer and editor based in Portland, Oregon. His work has appeared in Breaking Energy, National Geographic's Energy Blog, The New York Times, San Francisco Chronicle and elsewhere.

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