Tokyo has implemented a cap-and-trade program since 2010 to reduce CO2 emissions from large commercial and industrial facilities. The program requires these 1300 facilities to reduce emissions by 6-17% and allows trading of allowances. After the first year, emissions were reduced 13% and most facilities exceeded their targets. The program helped Tokyo prepare for energy shortages after the Fukushima disaster and spurred investment in green buildings. Cities can collaborate through alliances to share knowledge and experiences with emissions trading programs.