Wednesday, April 13, 2011

Natural gas is mostly methane

Natural gas is mostly methane: "

In my piece on the Cornell study, my subhed was “Leakage of methane from fracking boosts shale gas global warming impact.” I didn’t note until several paragraphs later that “Natural gas is composed largely of methane,” which comes from the second sentence of the study itself.

But as our bunny friend Eli pointed out yesterday, it seems like not everybody covering the subject is entirely clear on that:

… from Eve Troeh on Marketplace (NPR)

On TV, natural gas gets sold as pristine energy.

Robert Howarth: But that of course is only part of the greenhouse gas footprint.

Cornell University professor Robert Howarth. His new study is the first to quantify the whole carbon footprint for natural gas. He found it’s more Bigfoot than Bambi. Because when you crack shale to get to the clean-burning fuel, out comes “methane” — another greenhouse gas. He says that’s worse than burning coal.

And, of course, not to be caught in the rush, Friend Kloor jumps in at his new day job.

Maybe, but that natural gas bridge might not be as sturdy as previously thought, according to a Cornell University study in the upcoming May issue of Climatic Change Letters. Cornell ecologist Robert Howarth, a lead author of the study, says in a university release that methane (a potent global warming gas) leakage from a controversial drilling method (known as fracking) offsets the lesser carbon emissions that makes makes natural gas more attractive in comparison other fossil fuels:

You know, who would have guessed that natural gas is mostly methane.

I’ve been working in the energy arena for over two decades and sometimes forget to lead with the basics. Shale gas is “natural gas produced from shale.” Wikipedia notes “Methane is the major component of natural gas, about 87% by volume” though other sources typically give a range of around 70% to 90%. Most of the rest of nat gas is ethane, propane and/0r butane. The stuff that gets to your home “is almost pure methane.”

Methane is CH4 and its combustion produces heat and H2O and CO2.

Methane is a very potent greenhouse gas, though with a much shorter lifetime in the atmosphere than CO2. Recent studies suggest a very high global warming potential [GWP] for CH4 vs CO2, particularly over a 20-year time frame. If one is talking about building new natural gas power plants — or vehicles and fueling infrastructure — then I think it is reasonable to look at the 20-year GWP because you are making a commitment to long term natural gas use, which is to say long-term of methane combustion and whatever leakage or fugitive emissions occur along the way.

Hope that clears things up.


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