Developers in San Francisco are now required to think green when building most new commercial buildings and residential high-rises.

An ordinance signed Monday by Mayor Gavin Newsom forces many builders to meet a set of development standards called Leadership in Energy and Environmental Design.

The ordinance was touted by Newsom as one of the most aggressive in the nation. Operation and construction of buildings account for half The City’s carbon dioxide emissions, Newsom said.

California is already one of the leading states in the country with over 1,000 LEED-certified buildings. In San Francisco, 75 buildings have been certified through the program, according to the U.S. Green Building Council.

The ordinance was passed unanimously by the Board of Supervisors last month.