It's a trend that could leave small towns green with envy. According to a new report from the American Institute of Architects (AIA), programs designed to encourage more environmentally friendly building construction have grown by a whopping 400 percent in U.S. cities since 2003.

The numbers are relative. The report, titled “Local Leaders in Sustainability,” examines the growth and effectiveness of so-called green building policies in 661 cities with populations greater than 50,000. Only 92 of the cities examined—14 percent—were found to have some sort of green building program in place. The AIA expects that figure to rise to 20 percent next year. It also asserts that the total number of cities with green building programs is greater because many smaller communities with programs were not represented in the study.

Highlighted programs include such features as “green grants,” which permit streamlining for buildings with LEED certification and green design assistance. The study finds that the western region of the United States has the most cities with green programs. Forty-two cities in six states—46 percent of the cities in the report—have green building programs.

The movement toward more green building has gained momentum as politicians, city officials, architects and builders focus on the degree to which buildings and their construction contribute to greenhouse gases. According to the report, buildings currently account for nearly 50 percent of all greenhouse gas emissions, and the design and construction of green buildings will have a significant impact on the effort to reduce these emissions.