Environmental concerns and national security intersect in the debate over energy policy. Ever since the "Arab oil embargo" of 1973 created fuel shortages and gas lines in the United States, presidents and politicians have advocated energy independence for the country. Yet today the country continues to import more than half of the oil it consumes as demand for the world's supply is expanding markets like China and India. Public policy in the United States has improved mileage standards for cars and trucks built energy-conservation techniques into home and business construction. A recent spike in oil prices has again contribute to an expansion of alternative, domestic fuels like wind and solar although those remain a relative small source of power. Instead the United States relies on it abundant supply of coal, a source of airborne carbon scientists cite as contributing to global climate change, for nearly half of the nation's electricity. Nuclear power, once hailed as a cheap and universal source of electricity, instead stalled after the 1970s in the face of construction costs, waste issues, environmental protests and high-profile accidents. Beginning early in 2010, however, the Obama administration has announced loan guarantees and other actions intended to build new nuclear power plants as critics continued to point out the problem of long-term storage of nuclear waste has not been resolved. In 2012 federal agencies reported the U.S. reduced its dependence on foreign oil imports from 57 percent of consumption in 2008 to 45 percent due in part to increased domestic production. Since 2009 he U.S. has been the largest producer of natural gas in the world.