One More Round in the Methane Debate

I have a new note in the Journal of Geophysical Research (JGR) that I hope will be the last word in an increasingly tedious battle over an isolated but highly publicized methane leakage study that was published last year. I’ll explain what the note says in a moment, but first some background is in order.

Last fall, JGR published my critique of a highly publicized study (also published in JGR) from a team at NOAA. The study had claimed massive leakage rates for methane from natural gas production. Methane is a potent warming gas; the results, if correct, were a bombshell. My critique was simple: the original study had made unsupportable assumptions; if you removed those and instead used more of the data that the NOAA team had collected, you found implied methane leakage rates far lower than what the NOAA team had estimated.

No response from the original authors was published alongside my critique. This is unusual – it happened because the original authors did not submit a publishable response after being given half a year to do so. (My accepted paper was held from publication while JGR waited, which is normal, even if the waiting period was on the long side.) A couple months after my critique appeared, JGR published a NOAA-team response. The response claimed to a find fatal flaw in my paper and doubled down on their original claim that their data revealed methane leakage well above accepted estimates. Because the NOAA response had been accepted so late, I wasn’t given an opportunity to defend my paper at the time. Soon after, a similar team of researchers announced preliminary (pre-review) results from another study, claiming even more massive methane leakage in Utah. These once again attracted considerable attention.

When I read the NOAA response in November, I was stunned. The supposed fatal flaw in my paper didn’t exist; the NOAA authors had conflated a math trick with a physical phenomenon and drawn conclusions from that. The NOAA authors did, however, argue that a data set that they had relied on in their paper, and that I had retained in mine (though with expressed concern), was shaky. They then used that to assert that my results weren’t to be trusted. What they didn’t mention was that if their data set was unreliable, then their own results had no foundation either.

I quickly submitted a new note to JGR that made these points. It spent a couple months bouncing around in peer review because – and I find this kind of amazing – someone had found an additional flaw in the NOAA paper that I had not critiqued, and insisted that I needed to tackle it. My reply, including the additional requested critique (I swear I wasn’t trying to pick another fight), was finally accepted a few weeks ago.

The paper in press is here for JGR subscribers; you can download a preprint here. In it, I defend my paper from one NOAA-team criticism, but accept that their critique of the data set (“flashing profiles”) that they introduced and relied on may be correct. I then explained the consequences of that for both their analysis and mine. Here’s my bottom line from the newest paper:

“One can only conclude that either the flashing profiles are reasonably representative – in which case Petron et al [2012a] have presented no reason to question the results in Levi [2012] – or the flashing profiles are unrepresentative, in which case neither Petron et al. [2012] nor Levi [2012] have any basis to report reliable estimates of fugitive methane emissions. In either case, the results reported in Petron et al. [2012] are without foundation. Since the flashing profiles of condensate tanks in the area under study have likely changed since Petron et al. [2012] collected their data in 2008 (Petron et al [2012a]), this part of the debate is unlikely to be resolved definitively. Debate and observations should focus on rigorously understanding what is happening today through multiple observational and analytical methods. Several data collection efforts that could enable this are currently underway [EPA, 2012].”

I hope that we can do just that: focus on serious measurements that are underway while putting this flawed study behind us.