Tue December 20, 2011

Cornell scientists face off over danger of methane emissions

In April, Bob Howarth and two of his colleagues at Cornell University published a report in the journal Climatic Change, with this conclusion:

Natural gas is a dirtier fuel source than coal or oil.

The piece caused an uproar among energy analystsindustry insiders and researchers, and the result is a new article - set to come out in the same journal - by another Cornell professor, that directly contradicts the initial study:

Natural gas is a cleaner source of energy than coal.

And it's panning out to be a showdown.

Squaring off

Howarth argued in the initial study that natural gas' tendency to escape during drilling, processing, and transportation is bad news for the atmosphere.

"If you look at the range of methane on the time scale of a couple of decades following emission, and if you use the latest estimates on the relative importance of methane compared to greenhouse gas, no matter what you use as an estimate for leakage, the conclusion would be that this is a really dirty fuel from a greenhouse gas standpoint," says Howarth.

But in the new report, by Cornell earth and atmospheric sciences professor Larry Cathles, Howarth's conclusions come under heavy fire.

Cathles' three main criticisms:

  • Estimates of methane leakage are greatly exaggerated in the Howarth study. No one knows exactly how much methane leaks from the whole system (from well to storage to transport to the end-user). Howarth offered a range of up to 7.9 percent of total production from each well - Cathles says it's more like 2.2 percent.
  • The comparison with coal should be made based on the amount of electricity produced, as opposed to the heat produced. Howarth compared the greenhouse effects per unit of heat produced for natural gas and coal. Cathles says that is incorrect because coal is used mostly for electricity production. Natural gas is a much more efficient way to produce electricity and it could potentially replace coal in our power plants. So to say that natural gas is dirtier than coal, you have to compare it based on what coal is used for.
  • The comparison should have been based on a 100-year effect on global warming, what's known as Global Warming Potential (GWP). Howarth looked at both the 20- and 100-year effects of global warming. The old 100-year GWP of methane is 21 times more powerful than carbon dioxide, according to the Environmental Protection Agency. Either way, Cathles contends that Howarth used a GWP for methane that is much higher than what they should have used.

Cathles says when you add each of those mistakes together, Howarth is way off base in his conclusion.

"They were off by a factor of 20," Cathles contends. "And you can turn anything good into anything bad by multiplying one of them by a factor of 20."

The response

Howarth and his co-authors are not accepting defeat though. They've submitted a response that will also be published by Climatic Change, alongside the new Cathles report.

"I think some of these criticisms, people assume no one will bother to go back and read our actual paper," says Howarth.

Here's a summary of Howarth's defense:

  • The Howarth paper offers a range of emissions, with 7.9 percent of total production leaking sitting at the high-end of that range. Howarth says you get the same conclusions with the low-end of that range, 3.6 percent. "Our low-end estimates are somewhat lower than the EPA numbers, our high-end estimates are higher," he notes.
  • The Howarth paper did look at electricity produced, but focused on heat, because natural gas is used mostly for heating homes. "Our conclusion is not sensitive to that in any case," he says.
  • The authors also looked at both the 100-year and 20-year timeframes for methane's impact on global warming. Howarth stresses the 20-year timeframe because of the sense of urgency among many climate scientists, that curtailing greenhouse gas emissions is an urgent matter. Howarth says, "if one is concerned about global warming, we have got to do everything we can to reduce methane emissions."

Not surprisingly, Howarth says the criticisms of his original paper are all way off-base.

The conclusion is really only sensitive to the time frame, whether you want to look at the decadal timeframe or you want to look at the century time frame. And also whether you want to use the latest available science for what the relative global warming potential for methane versus carbon dioxide is or not. A lot of our critics like to use outdated information on that. I think that’s rather indefensible as well.

Escaping methane

What a lot of the arguments boil down to is how much methane escapes during the drilling process - and what impact that escaped methane has on the atmosphere.  The science around this issue is unsettled, but is starting to gain attention among opponents to hydrofracking.

In the above video, courtesy of the Chesapeake Bay Foundation, an infrared camera captures methane emissions from hydrofracking operations.

Methane, the primary component of natural gas, is odorless and colorless when it comes out of the ground. No one knows for sure how much methane hydrofracking wells emit, but the Chesapeake Bay Foundation says this video indicates that it may be much more than previous estimates.

Why it matters

Supporters of natural gas often describe it as a "bridge fuel" - something to help get us off coal and oil until wind and solar and other renewables can meet energy demand. 

A bill in Congress would give tax credits to people who buy natural gas-powered vehicles and to companies that build natural gas fueling stations. President Obama has offered his support to the bill, which has 181 co-sponsors. Beyond transportation, utilities are beginning to transition coal-fired plans to natural gas.

These efforts are going forward despite the debate over whether or not natural gas is in our best interest in the short-term - the desire to  get off coal, cut back on carbon dioxide,create jobs and reduce dependence on foreign oil is winning out.

But the toll that will take on the atmosphere remains unknown.