Researchers at Cornell University are raising alarms over the expected increase in use of natural gas from shale deposits. They argue that replacing coal and gasoline with natural-gas alternatives could worsen, rather than improve, the impact of greenhouse gases. The greenhouse-gas footprint of shale gas over a 20-year period is at least 20 percent higher than that of coal and "perhaps more than twice as great," they say in a study published online in the journal Climatic Change. The culprit is the leakage of methane, the main component of natural gas.

To extract natural gas from shale, drillers hydraulically fracture the rock by injecting a cocktail of water and chemicals into a horizontally drilled well at high pressures. Robert Howarth, a biogeochemist and professor of earth sciences at Cornell, argues that a significant amount of gas also mixes with the water-chemical mix and escapes into the atmosphere when the fluid returns to the surface. The drilling out of well plugs that separate fracking stages also results in temporary emission releases, giving shale gas a "significantly larger" greenhouse-gas footprint than conventional natural gas.