I blogged last week about the implications of the findings of a paper by Professor Robert Howarth and colleagues at Cornell University. The paper compares the carbon footprints of natural gas and coal and concludes that – because of methane leakage – natural gas contributes to global warming as much as coal, or even more, when assessed on a life-cycle basis. While I have questions about the emissions estimates in the paper, it has brought attention to an important fact.
Namely, that we need better data to accurately characterize air pollution from natural gas development and determine with confidence the associated health and climate implications.
Media coverage over the past week was extensive. A Washington Post editorial hit the bull’s eye. Unfortunately, not all the coverage has been 100% accurate – perhaps owing to the technical nature of the issue and the paucity of solid data about methane emissions associated with natural gas systems.
In particular, I want to clarify a reference in a New York Times column to Environmental Defense Fund “estimates of methane gas emissions that are 75 percent lower than Howarth’s.”
Though we appreciate Joe Nocera’s consideration of our work, the statement in the Times’ column is misleading in two ways. First, the estimates EDF relies on are not our own, but rather taken from the Environmental Protection Agency (EPA), which just finalized its 2009 inventory of greenhouse gas emissions. From EPA’s inventory, we estimate that at least 2.2% of gross natural gas produced in the U.S. is released to the atmosphere. This estimate is highly uncertain, as evidenced by EPA’s recent revision that doubled its estimates from as recently as last year.
Second, Professor Howarth’s paper uses a different metric: how much methane is leaked as a percent of the total methane produced over the life of an unconventional gas well. The paper reports this value to be 3.6% and 7.9% as the low- and high-end estimates. Assuming these different metrics can be directly compared, EDF’s estimate of the methane leak rate is 39% lower than Professor Howarth’s paper’s low-end estimate and 72% lower than the high-end estimate. It is unfortunate that the Times’ column only made the comparison with the paper’s high-end estimate.
The only way we can gain confidence about the climate benefits of natural gas relative to other fuels is by obtaining more accurate data about the amount of methane released during the production and distribution of natural gas. And as I have said before, this is something the natural gas industry – which claims to provide the “low-carbon” fossil fuel – should support.