A report by the Brookings Institution quantified the amount and most significant sources of carbon emitted by the 100 largest metropolitan areas in 2000 and 2005.

Researchers said variations in the carbon footprints of metropolitan areas are related to development patterns, transit options, freight traffic, carbon content of electricity sources, electricity prices and weather.

"Federal policy could play a powerful role in helping metropolitan areas --and so the nation-- shrink their carbon footprint further," the Brookings Institution said Thursday in a news release.

The New York Times said Honolulu had the lowest per-capita carbon ranking, followed by the Los Angeles-Orange County area, the Portland-Vancouver area and the New York metropolitan area. Toledo and Cincinnati, Ohio, Indianapolis, Ind., and Lexington, Ky., had some of the highest levels of carbon emissions per capita.