text: The economics also work against a major transformation in the technology of producing power, either mobile or stationary. Coal is cheap. Natural gas is becoming even cheaper, but its carbon emissions, according to the U.S. Energy Information Administration, are still half those of coal and three-quarters those of gasoline per unit of energy produced. Although a switch to natural gas for many power uses would help, and accounts for recent drops in U.S. emissions, it cannot change the carbon arithmetic enough to prevent the world from exceeding "safe" levels.