Though major cities sit on just 2% of the world’s available land, together they produce in excess of 77% of the globe’s CO2 emissions. Cities might be major polluters, but they’re also major centers for innovation. That’s made urban cityscapes the focus for sustainability and green efforts by environmental groups.

Washington D.C.’s Green Building Act of 2006 and the D.C. Green Construction Code together have made the nation’s capital a leader in per capita square footage of Leadership in Energy and Environmental Design (LEED) certified space. D.C. has also ranked first for the EPA’s Energy Star cities list for three years in a row. The numerous awards culminated in the U.S. Green Building Council naming Washington D.C. the globe’s very first LEED Platinum City last year.

Using D.C.’s success as a model, cities around the country are looking to boost their sustainability. Observers attribute D.C.’s success to both good construction practices and green-conscious urban planning. Cultivating a tree canopy, paving more bike lanes, and pushing for more walkable cities are all steps in the process toward making cities around the world friendlier for the earth and, as a consequence, friendlier for humans.