WASHINGTON, D.C. —
This study, however, was based on nearly 13,000 measurements from airplane flights and tall towers, the most used in any such research.
The information was collected in 2008, right at the beginning of the natural gas boom from hydraulic fracturing. So these measurements, which will be repeated for 2012, don’t include much impact from fracking, Michalak said. Studies recently have shown conflicting results about how much methane escapes during fracking and other forms of fossil fuel drilling.
Outside experts praised the study. Robert Howarth at Cornell University called “it very compelling and quite important. This is the most comprehensive study yet.”
Michalak said because of the way they measured methane — just looking for it in the air as opposed to tracking it from a source — it is hard to say what is putting more methane into the air. But she said by looking at concentrations — especially within Texas, Oklahoma and Kansas — the scientists have a good idea: Cows, oil and gas.
Nearly one-quarter of the U.S. methane emissions came from those three states. Texas is by far and away the No. 1 state for refineries that turn oil into gasoline. Texas and Oklahoma have been big oil and gas drilling states and Kansas is a big cow state.
Cows seem to be spewing twice the methane that scientists previously thought, Michalak said.
While burps and flatulence are part of the methane emission from cattle, University of California Santa Barbara professor Ira Leifer said a bigger factor is manure.
“If you shovel it into an artificial lagoon you are creating the perfect production for methane, but it cuts down on the smell and your neighbors complain less,” he said.