What's wrong with this carbon footprint?

It was, the Brookings Institution admitted, a flawed study. But it's the best data we have on the impact of urban areas on climate. This business of quantifying carbon emissions is as complicated as technological urban life itself.
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While Puget Sound ferries are jammed, the state makes it hard to afford new ones. (Chuck Taylor)

It was, the Brookings Institution admitted, a flawed study. But it's the best data we have on the impact of urban areas on climate. This business of quantifying carbon emissions is as complicated as technological urban life itself.

Like other papers, the Seattle Post-Intelligencer had a story on the Brookings Institution's new study ranking the carbon footprints of 100 major cities [392K PDF] in America. Northwest cities do rather well. Portland ranks third, Boise fifth, and Seattle sixth for lowest carbon emissions per resident. But the study's rankings also suggest that some of our most cherished notions about how to live "green" aren't borne out. Also ranking in the top 10 are sprawling car-centric cities like Los Angeles (2) and San Diego (10). L.A. has a better carbon footprint than Portland? What gives?

That same question baffled the Los Angeles Times, but they found further explanation in the report's caveats, which are significant:

The calculations did not account for the fact that half the [L.A.'s] electricity comes from coal-fired power plants. Instead, Brookings used a state-wide average that included the hydroelectric and nuclear plants in Northern California.

Omitted from the data are emissions from industries and commercial buildings, and from local roads apart from federal highways.

The researchers also chose metropolitan statistical areas, as defined by the U.S. Census Bureau. Those areas may allow for a uniform geographical comparison, but in the case of the Los Angeles-Long Beach-Santa Ana area, that omitted commutes from as far as Ventura, San Bernardino or Riverside counties.

"The data is fuzzy," said Andrea Sarzynski, a senior research analyst at Brookings. "We do the best we can."

The New York Times reports that "the calculations do not include industrial emissions, those from commercial or government structures and those from air, rail or sea transportation."

Those seems like pretty major omissions.

The P-I reports that one problem with such studies is that there is no agreement on how to measure carbon emissions:

Another problem with these assessments, according to a local energy policy expert not involved in the project, is that nobody really agrees on how to measure a carbon footprint.

"There is no one perfect method for these calculations," said Anne Steinemann, a University of Washington professor of civil and environmental engineering. Steinemann and colleagues at Vanderbilt University recently analyzed carbon footprint methods and found them highly inconsistent.

One thing the study suggests is that cities are difficult to measure and quantify consistently, that they're complicated entities, and that factors other than sprawl and density and mass transit play a role in just how "green" a city is. A city with significant sprawl might still be greener than an older industrial city, for example. Or a car-centric place like Los Angeles might look better because, despite sprawl, it is also very dense.

Inconsistencies, caveats, and omissions aside, Brookings defends the analysis as a first cut at doing such rankings, but the study fulfills a larger Brookings goal, which is to focus on the urbanization of America and help steer federal policy toward our cities.

More than 800 cities have signed on to commit to carbon emission reduction goals set by the Kyoto agreement. Seattle Mayor Greg Nickels has made a name for himself helping to lead that effort. The challenge is a big one, since the country overall has been losing ground in the first half of this decade as our carbon footprint is expanding, not declining. The Los Angeles Times reports: "Emissions from residential, commercial and transportation sectors each increased by more than 25% over the last 25 years, the report notes, while industrial emissions declined as manufacturing dwindled."

Increases are happening even in some of the top-ranked cities. For example, Seattle's carbon footprint from transportation and residential use has dropped, while Portland's has actually increased, according to Brookings.

Flawed and limited as it is, the Brookings report is politically timed:

Next week, the U.S. Senate is expected to take up legislation to limit carbon emissions nationwide. Its provisions, which include a cap-and-trade system for greenhouse gases, are highly controversial, and Brookings wants aggressive measures to encourage climate-friendly cities.

The task of defining them is still a work in progress.


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About the Authors & Contributors

Knute Berger

Knute Berger

Knute “Mossback” Berger is Crosscut's Editor-at-Large.