The main contribution of President Obama’s Climate Action Plan, as Raymond Pierrehumbert explains, is its charge to the Environmental Protection Agency to regulate the carbon emissions of existing power plants. This could reduce U.S. carbon emissions significantly—but if the EPA uses the dubious set of calculations that the government has developed, its power plant regulations might be struck down in court. The story behind those calculations reveals the immense challenges the government faces as it finally addresses global warming.
Although many gases contribute to climate change, the major culprit is carbon, which diffuses into the atmosphere when fossil fuels are burned. Carbon is emitted in vast quantities and takes a very long time to dissipate. Thus, any effective regulation must take aim first and foremost at carbon.