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Beefing Up Population Density Won't Curb Greenhouse Gas Emissions

Beefing Up Population Density Won't Curb Greenhouse Gas Emissions

City dwellers tend to have smaller carbon footprints than their suburban neighbors. They use more public transportation and live in smaller abodes, whereas folks in the suburbs own more vehicles, have bigger homes, and enjoy larger household incomes, all of which increases one's capacity for emitting climate-heating greenhouse gases.

Thanks to researchers at UC Berkeley, we now can picture how America's urban centers are locked inside vast rings of emissions-spewing sprawl. Chris Jones and Kamini Iyer, who work at the university's CoolClimate Network, have plotted the 2013 household carbon footprints for nearly every American zip code on one zoomable, color-coded map. Cities emerge as jade-colored oases plopped in feverish, crimson-hued deserts, looking (in the words of Jones) like "carbon-footprint hurricanes, with dark green, low-carbon urban cores surrounded by red, high-carbon suburbs."

Drag your mouse over neighborhoods to reveal the startling contrasts. The zip code of 20008 in the Northwest quadrant of Washington, D.C., has an annual household footprint equivalent to 40 metric tons of CO2. However, just a few miles west in the tony 'burbs of Potomac, Maryland, and Great Falls, Virginia, the footprint swells to between 85 and 93 metric tons. Manhattan and Brooklyn homes trend toward tons of yearly carbon emissions in the 30s and 40s, but over in Long Island you'll find it's more normal to have loads in the 60s and 70s (or in 11568, aka Old Westbury, the equivalent to an incredible 95 tons of CO2). The typical household footprint in the United States in 2011, for comparison, was only 48 metric tons.

This gas-hazed cartography, published in Environmental Science & Technology, indicates that suburbs are responsible for 50 percent of America's household emissions – despite less than half of the population living in these areas, researchers say. The average footprint for households in major metropolitan areas hovers at about half the national average; for homes in the distant suburbs, the footprint can be twice as large as average.

Just what contributes to a particular suburb's climate profile often hinges on geography. Emissions in the California 'burbs tend to be driven by automotive transportation, for instance, whereas in the Midwest they're more likely to come from coal-firing plants supplying electricity to homeowners. The Berkeley team hopes their highly local breakdown of climate data (visible when you swoop over a zip code) will help governments devise mitigation strategies better suited to their particular situations.

In the meantime, here's one strategy that's doomed to fail: Trying to beef up a city's population density. Warn the researchers:

Efforts to increase population density, for example, appear not to be a very effective strategy locally for reducing emissions. A 10-fold increase in population density in central cities yields only a 25 percent reduction in greenhouse gas emissions.

"That would require a really extraordinary transformation for very little benefit, and high carbon suburbanization would result as a side effect," Jones said.

Another probable losing plan would be doing the same thing in the suburbs, they say:

Increasing population density in suburbs appears to be an even worse strategy, he said. Surprisingly, population dense suburbs have significantly higher carbon footprints than less dense suburbs.

"Population dense suburbs also tend to create their own suburbs, which is bad news for the climate," explains Jones.

How's your own household rate among the 31,000-plus zip codes analyzed by Berkeley? Here's a sampling of a few large cities, starting with New York's suburban inflammation:

The San Francisco Bay Area:

Washington, D.C.:

Denver:

Minneapolis:

Atlanta:

Maps courtesy of UC Berkeley's CoolClimate Network, "Average Annual Household Carbon Footprint (2013)"

John Metcalfe is a staff writer at The Atlantic Cities. All posts »

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