More energy-efficient buildings and more riders using public transit helped Sacramento finish at No. 12 on a list of the nation’s best cities with the lowest carbon footprint per resident. The average person in the Sacramento region had a carbon footprint of 1.77 metric tons in 2005, that’s a 9 percent decline from 2000. A 10 percent reduction in energy use in homes coupled with an 8 percent drop in transportation — largely because of increased mass transit ridership — greatly helped lower the carbon footprint of residents in Sacramento. Honolulu took the nation’s top spot, followed by Los Angeles and Portland, Ore., while Stockton finished at No. 19. Lexington, Ky., had the worst carbon footprint of the 100 cities studied by The Brookings Institution.