For cities, the motivation is twofold. All the hand-wringing over climate change has prompted more cities to do their part to contain greenhouse-gas emissions that most scientists believe are causing global warming. In the U.S., more than 700 mayors have signed an agreement to try to follow the Kyoto Protocol’s goal of reducing greenhouse-gas emissions — even though the Senate has rejected the treaty.
The other major motivation for cities: energy costs, which have more than doubled since 2000. Strapped for cash, municipalities are scrambling to save as much money on energy use as they can.