Portland, OR Portland heads most lists of America’s greenest cities. Mayor Sam Adams, whose term ended on Dec. 31, 2012, said in his first State of the City Address in 2009 that he hoped to make Portland the most sustainable city in the world. Over half of Portland’s energy comes from renewable sources. Adams worked to replace dirty energy suppliers with cleaner sources, and set up Clean Energy Works, a first-in-the-nation program that gives homeowners free energy assessments and provides $2,000 rebates and loans for home retrofitting. He also started a curbside composting program that has resulted in a 38 percent drop in the city’s trash output.