One of the reasons the Bay Area performed well was the weather - which allows residents to not rely on air conditioners or heating that is needed in other parts of the country.
The San Jose and San Francisco metro areas performed well because fewer people are driving cars and opting for mass transit.
The study also includes two of the largest components of carbon emissions - which is gas use on the roadways and energy used in homes; those two factors account for a little more then half of the carbon emissions in the United States.
Smallest U.S. carbon footprint from the Brookings Institution
2. Los Angeles
7. San Jose, Sunnyvale
8. SF, Oakland, Fremont
10. San Diego
Largest U.S. carbon footprint
The Brookings Institution used information from the U.S. Census Bureau to figure out commute patterns and used statewide averages to calculate electricity costs. So it is not exact science, but the study's authors say it is the best material available.
Emissions from commercial buildings, factories and other non-highway transportation were omitted from the study. The Brookings Institution will re-factor in those numbers and come out with a new study either later on in this year or early 2009.