According to the U.S. Environmental Protection Agency, greenhouse gases (GHG) are gases that trap heat in the atmosphere. In 2010 alone, U.S. GHG emissions totaled 6,821.8 million metrics tons of carbon dioxide (CO2). California leads the nation in working to reduce the level of GHG emissions. In 2006, the State Legislature passed Assembly Bill 32, also known as the Global Warming Solutions Act that directs the state to reduce statewide emissions to 1990 levels by 2020, a 17 percent reduction. High-speed rail is part of the state’s GHG reduction strategy.