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PRI's Environmental News Magazine

Gas Studies Ignite Controversy

Published: August 11, 2012


By Jeff Young


(photo: C.A. Muller)

Cornell and MIT in war of words over fracking gas and global warming. Does the heated exchange shed any light?

By Jeff Young

Authors of two studies on natural gas have exchanged some heated words as they try to suss out the fuel’s impacts on climate change. As Living on Earth
reports this week, MIT and Cornell University researchers reach very different conclusions about the greenhouse gas emissions that might result from increased use of gas. Cornell Professor Robert Howarth’s study concludes gas from hydrofracking of deep shale deposits could emit more greenhouse gases than does coal.
MIT’s reports includes a section
criticizing Howarth’s paper. Further, at a press event, some MIT authors took shots at Howarth’s study. MIT management professor Henry Jacoby called it “a really poor piece of work.”

Following up on an interview with Living on Earth, Prof. Howarth shot back:

“The MIT studies have not been subject to any serious peer review, and have been largely or totally funded by the oil and gas industry. I do not feel this is credible science, but rather is part of the oil and gas industry public relations effort… paid advocacy dressed up in the language of science.”

To which MIT responded, in a statement:

“The work is…reviewed by a diverse and knowledgeable external advisory group with backgrounds in oil and gas, environmental stewardship, natural gas use, and demand management. The report contents are, however, the sole responsibility of the study group…the sponsors obviously have an interest in the subject but are granted no authority to influence the results and serve as reviewers in the same capacity as advisory committee members.”

Goodness. But let’s set aside the heat for a moment (the atmosphere has enough of that, after all) and see what light might be shed here.

There are three areas where the Howarth study has taken criticism: 1) the estimates of the methane that leaks from deep shale gas drilling (fracking); 2) the efficiency rate for burning natural gas; 3) the time frame used to measure the warming potential of different greenhouse gases. I call these the Leaks, the Burn, and the Impact. Here’s a bit of what we’ve learned on these points.

THE LEAKS
On the leakage, called fugitive emissions, MIT used the latest EPA figures available. MIT’s authors wrote that Howarth’s conclusions were “strongly influenced by unsubstantiated estimates of methane emissions.” In a similar vein, the Department of Energy’s National Energy Technology Lab’s work on gas leaks found much of the unaccounted for gas isn’t really lost to the atmosphere, but is actually used to power equipment.

In the Living on Earth interview, Howarth explained: “Their [NETL] analysis did indeed use a national database to look at lost and unaccounted for gas and in order to do that you need to account for what’s burned or lost along the way. We actually played with some of those numbers and decided those numbers were too uncertain to use so we didn’t use those. We used lost and unaccounted for gas data from the state of Texas.”

On this point, there seems to be agreement that much more work is needed to better measure the real losses of methane and for the industry to do a better job of capturing gas at its drilling operations. MIT recommends that “EPA and DOE co-lead a new effort to review and update methane emissions factors with broad-based stakeholder involvement and with actual emissions measurements.”

THE BURN
MIT places emphasis on the higher efficiency of most natural gas power plants compared to coal-fired power plants. The higher the efficiency, the less CO2 emitted per unit of energy. MIT writes “results in the Cornell study for gas vs. coal in electric generation are based on the heat content of each. In fact, replacement of coal by natural gas in U.S. electric generation would involve the substitution of coal units with an average efficiency of 30% to 35% with gas combined cycle plants with efficiencies in the range of 45% to 55%.”
In other words, they think Howarth used too low an estimate of the efficiency of gas-powered electricity.

In the interview, Howarth explained that he used a range of efficiency estimates because he didn’t think focusing just on electricity production was the best view.
“We did not look at final efficiencies for any of the potential uses…If you focus on electricity, at the moment about 30% of gas is used in electricity. We thought to focus simply on using natural gas for electricity production was wrong. Most is used in residential, commercial and industrial uses.”

Howarth doesn’t think the new production of shale gas will move into the power sector so much as replace other supplies of gas drilling.

“What seems more likely is that shale gas will replace conventional gas for uses it’s put to now, with some modest increase in industrial use,” he said.

Part of this difference appears to stem from the assumptions the different studies make. MIT’s study assumes a carbon price of some kind, and finds that a price of $16 per ton of CO2 will quickly shift some gas into the power sector, displacing coal.
Howarth uses DOE projections about gas use that do not include any price on carbon.

THE IMPACT
Now we’re really down into the wonky weeds, but let’s face it: if you’ve read this far, you’re an energy geek. Just accept it.

Climate scientists use complex models to come up with a way to compare the relative warming impact of different greenhouse gases. In this case, we’re looking at the global warming potential of methane versus carbon dioxide. Methane is a potent greenhouse gas, but lasts in the atmosphere only a dozen years or so. CO2 can persist for centuries. The models come in three flavors, 20-year time frame, 100-year time frame, and 500-year time frame.

MIT writes: “The IPCC decided to use the 100-year measure, and it is a procedure followed by the U.S. and other countries over several decades. An outlier in this domain is the Cornell study which recommends the application of the
20-year value in inter-fuel comparison.”

The 20-year time frame emphasizes the impact of methane. MIT Energy Initiative Director Melanie Kenderdine said, “The concern of the climate scientists here is that [use of the 20-year time frame] decreases the focus on what they believe is the more serious problem, which is CO2 emissions, which reside in the atmosphere for hundreds of years.”

Howarth’s study actually includes both the 100- and 20- year time frames (but the headline grabbing results came from the 20-year view). He told Living on Earth that the 20-year time scale is a useful one, given concerns about the climate approaching a tipping point in the coming decades.

“We’re in a stable state at the moment, relatively stable, but if we force it into some new trajectory, past some tipping point, then society’s in a lot of trouble. The shorter time frame is critical if you’re serious about dealing with global warming.”

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