In the years immediately after it's released, methane is a potent greenhouse gas. It causes 86 times as much global warming over a 20-year period as carbon dioxide, the single largest contributor to climate change. According to our analysis at Energy Innovation, the methane missing from the EPA's inventory — in terms of the contribution to global warming over a 20-year time period — would be equivalent to the greenhouse gas emissions of 252 coal power plants.
At the same time that the scientific community is finding evidence that methane is being under counted, the newly released draft version of the U.S. EPA's national greenhouse-gas emission inventory presents data showing that methane emissions from natural gas are falling. The new draft inventory releases 2012 data for the first time, and claims that emissions from methane fell by roughly 2 percent compared to 2011. The new draft inventory also revised downward estimates for past years because of new information about reduced emission well completions (the process that gets natural gas to start flowing) and other voluntary mitigation steps received from companies.