The most dramatic policy measure at the U.S. state level has been the passage of the California Global Warming Solutions Act (Assembly Bill (AB) 32), which seeks to limit GHG emissions from a wide range of industrial and commercial activities. AB 32 requires that California’s GHG emissions be reduced to 1990 levels by 2020 through an enforceable statewide cap and in a manner that is phased in starting in 2012 under rules to be developed by the California Air Resources Board (CARB).