The push to tap natural gas reserves locked in Marcellus shale formations beneath western Maryland and the rest of Appalachia is generating lots of debate over the risks to drinking water and streams posed by the extraction method, known as hydraulic fracturing, or "fracking."

Now comes a new criticism: Some researchers say all the shale gas wells being drilled may do more harm to the earth's warming climate than a comparable amount of coal mined via mountaintop removal.

That's a big switch if so, as natural gas generally emits half the climate-warming carbon dioxide coal does when burned.  Many have touted gas as a clean alternative to coal, and a suitable "transition" fossil fuel until more renewable energy sources can be developed.  Even those Maryland lawmakers most worried about the environmental and health impacts of "fracking" seem to accept that tapping shale gas is preferable to mining more coal or drilling for more oil offshore.

But researchers at Cornell University have projected that greenhouse gas emissions from shale gas production over the next 20 years could actually be higher than from surface-mined coal, possibly even twice as high. The researchers say they've submitted their findings for publication in a scientific journal, but have posted a summary here. 

The reason shale gas is worse for the climate, they say, is that methane in the gas is getting into the atmosphere from vents and leaks during hydraulic fracturing - and afterward, as the gas is being pumped out. Methane is a much more potent greenhouse gas, with 25 times more warming impact, pound for pound, than carbon dioxide. 

The Cornell scientists estimate that 3.6 to 7.9 percent of the methane in shale gas is leaking into the air, up to twice what escapes from conventional gas production.  Buttressing their findings is a November 2010 report from the Environmental Protection Agency, which reviewed the greenhouse gas emissions of various fuels and determined that natural gas, particularly shale gas, is higher than previously believed.

"Compared to coal, the footprint of shale gas is 1.2- to 2.1-fold greater on the 20-year time frame and is comparable when compared over 100 years," concludes Robert W. Howarth, professor of ecology and environmental biology.

Jeffrey McManus with the Chesapeake Climate Action Network warned lawmakers about this new evidence that shale gas is a "serious threat" to the climate during a hearing Wednesday in Annapolis on bills that would require tighter regulation or a two-year study of "fracking."   No one asked him any questions, or even seemed to pay much heed.

(Well being drilled near Pittsburgh.  2005 Baltimore Sun photo by Doug Kapustin)