Natural gas extracted from shale formations has a greater greenhouse gas footprint-- because of methane emissions--than conventional gas, oil and coal over a 20 year period. Methane emits 20 times the greenhouse gas emissions as does carbon. This calls into question the logic of using natural gas as a climate-friendly alternative to fossil fuels, according to Robert Howarth and colleagues, from Cornell University in New York. Their work research is published online in Springer's journal,Climatic Change Letters. Natural gas has long been touted as a fairly clean source of fossil fuels, but that was when it was derived as a byproduct of oil refining. Now, with increasing reliance on fracking from shale formations underground, the picture is very different.