A new study on the environmental impact on natural gas drilling in shale has found that the process known as “hydraulic fracturing” may contribute to global warming as much as coal, or even more, because large amounts of methane, a greenhouse gas, are escaping into the atmosphere during the process. For years, advocates of “fracking” have promoted natural gas as a clean alternative to coal. In the new study, Cornell Professor Robert Howarth writes, “Compared to coal, the footprint of shale gas is at least 20 percent greater and perhaps more than twice as great on the 20-year horizon, and is comparable when compared over 100 years.”