However CH4 is a gas, it leaks (an average of 3.3% in the US and up to 7.9% for unconventional gas from fracking shale deposits according to Robert W. Howarth, Renee Santoro and Anthony Ingraffea, ???Methane and the greenhouse-gas footprint of natural gas from shale formations???, Climatic Change, 2011) and is 105 times worse than CO2 as a GHG on a 20 year time frame and including aerosol impacts