How Does Your City's Carbon Footprint Stack Up?

With its balmy climate and residents who would rather go to the beach than drive on an interstate, Honolulu has the smallest metropolitan carbon footprint in the United States.

By way of contrast, mix an icy Kentucky winter with coal-fired power plants and residents who often hit the highways, and you end up with the metro area of Lexington-Fayette, Ky., rated as having the largest carbon footprint in the nation.

These two extremes are part of a report issued Thursday by the Brookings Institution in Washington, which looks at the per capita carbon footprint of the 100 largest metro areas in the US, based on residential energy use and highway transportation. The smallest carbon emissions are generally in warmer areas or cities with a highly developed public transit system. Most are in the West.

The worst emitters are mainly in the mid-Southern and Midwestern parts of the US, areas subject to winter weather. Urban sprawl there has made for long commutes in automobiles, and most of the region's electricity comes from coal. The cost of energy in these areas is lower compared with metro regions with smaller carbon footprints.

The Brookings report is likely to be controversial since few cities want to be lumped at the bottom of the heap, and critics point out that it does not look at all aspects of carbon emissions. But the report may also help some cities and regions see how other areas are reducing their carbon emissions in their transportation systems, power generation, heating and cooling of homes, and even land use.

The report is coming out a week before debate is expected to begin in the US Senate on legislation that calls for a 70 percent reduction in greenhouse-gas emissions by 2050 and imposes a price on carbon emissions.

"To me, the greatest takeaways from the report are the relative efficiency of metropolitan and urban areas, the variation of their performance, and the multiple influences that determine that," says Mark Muro, policy director of the Metropolitan Policy Program at Brookings. "Metros are responsible for a large amount of the nation's emissions but also offer the best prospects for large savings."

Partial data for emissions rankings

Mr. Muro is quick to acknowledge that the data are only partial, in large part because of the difficulty in obtaining accurate information. The two major sources of carbon-emissions data are 2000 and 2005 US Department of Transportation statistics on highway usage as well as information obtained from Platts, a subsidiary of McGraw-Hill, on residential energy usage. But the rankings do not include traffic on local roads or the emissions of commercial, industrial, or government users.

"We really have a fragmentary picture of the country," Muro says. "This is the beginning of the conversation."

Despite the shortcomings in the report, some groups still believe it has value. "It illustrates the importance of local governments since emissions are local and so are solutions," says Annie Strickler, a spokeswoman for ICLEI (International Council for Local Environmental Initiatives), an umbrella organization of local governments working on sustainability issues.

ICLEI, which is based in Oakland, Calif., is in the process of a more comprehensive rating of cities on sustainability. It will try to cover all sources of carbon emissions.

Some of the Brookings ratings may appear puzzling. For example, the Los Angeles area is rated second behind Hawaii. The L.A. basin is famed for smog and traffic backups. However, Muro says, the research underscored the density of the area's build-out. "While there are not a lot of tall buildings, it has places with a lot of small lots, master-planned large developments, and an increasing density," he says. "And the state is increasingly pulling out of dirty energy sources and requiring lighter, low-carbon sourcing."