Some Thoughts on Two Recent NOAA Methane Reports

Researchers at the National Oceanic and Atmospheric Administration (NOAA) recently released two reports, which estimate fugitive methane emissions from natural gas production on a global scale.  Their conclusion is that natural gas production has a world-wide methane leakage rate of between two and four percent since 2000, albeit with a clear downward trend.  Nonetheless, the researchers argue, “Further emissions reductions by the NG industry may be needed to ensure climate benefits.”

Importantly, the NOAA researchers do not take any new measurements of methane emissions from natural gas production.  Instead, in the first report, they estimate both natural and anthropogenic methane emissions from everything other than natural gas production (well not everything – more on that later).  They obtain that data from a number of previous studies and plug it into computer models.  In the second report, (which contains the whole project’s conclusions) the researchers then subtract those numbers from estimates of global methane emissions taken from NOAA’s global stations to come to an estimate for the leakage rate for natural gas production.

Here are a few important facts to know about NOAA’s latest conclusions.

Fact #1: Admits numbers are overestimates; doesn’t factor in natural petroleum seepage

Each time the final report states its conclusions – that methane leakage from natural gas is around two to four percent – it qualifies that conclusion by explaining that these numbers may be overestimated due to the fact that the study does not take into account what’s known as “natural petroleum seepage.”  Here are a few of the key excerpts from the report:

“The modeling suggests an upper bound global average FER [fugitive emissions rate] of 5% during 2006-2011, and a most likely FER of 2-4% since 2000, trending downward.  These results do not account for highly uncertain natural hydrocarbon seepage, which could lower the FER.”  (p. A; emphasis added)

“Using a global boxmodel and well-known quantities of global average atmospheric CH4, δ13C−CH4, and C2H6 mixing ratios, the most likely FER was found to be 2−4% since 2000, and currently (2006−2011) having an upper bound FER of 5%. Both results are potentially overestimated because these estimates exclude highly uncertain emissions from natural hydrocarbon seepage.” (p. G; emphasis added)

“The most likely global FER range (2−4%) is slightly higher than many recent bottom-up estimates (1.1−3.2%; full life cycle) in the U.S. and elsewhere; however, potentially unaccounted natural seepage could reduce our estimate.” (p. G; emphasis added)

The researchers also admit that “Tropical wetlands may be underestimated in particular.” (p. F)

Natural petroleum seepage is the release of methane from petroleum seeps, which are not related to oil and gas development. Several studies have concluded that methane seepage from naturally occurring events is actually quite high. One study – which looks at seepage from oil specifically – comes to this conclusion:

“Every year, natural petroleum seepage emits 0.2–2 Tg of oil to the ocean.  Significant oil seepage can build large underwater mounds, consisting of tar deposits with morphologies similar to volcanic lava flows, known as asphalt volcanoes.  Such events are typically accompanied by large fluxes of the greenhouse gas methane.” (emphasis added)

Another study by Giuseppe Etiope found that naturally occurring seepage is quite a significant source of global methane emissions.  From that report:

“Recent studies have shown that geological emissions of methane are an important greenhouse-gas source. Remarkable amounts of methane, estimated in the order of 40 – 60 Tg yr -1, are naturally released into the atmosphere from the Earth’s crust through faults and fractured rocks. The main source is natural gas, both microbial and thermogenic, produced in hydrocarbon-prone sedimentary basins and injected into the atmosphere through macro-seeps (onshore and offshore mud volcanoes and other seeps) and microseepage, an invisible but pervasive flux from the soil.”

The NOAA researchers actually mention this Etiope study, and here’s what they have to say:

Natural hydrocarbon seepage may be an additional significant source of atmospheric CH4 and C2H6 not currently accounted for in most top-down studies.  Visible macro-seeps, marine seepage, microseepage, and geothermal/volcanic areas may contribute between 40 and 60 Tg CH4/yr and 2−4 Tg C2H6/yr globally. While not included in Figure 1, adding 40 Tg CH4/yr and 2 Tg C2H6/yr in the model would reduce FER by about two percentage points (constant over time). The magnitude of the above seepage estimates have been challenged. Yet, having excluded any seepage in our main results (Figure 1) emphasizes that our FER may be overestimated.” (p. E; emphasis added)

As this quote makes clear, if the researchers had accounted for that 40 – 60 Tg of natural seepage in their study, that would “reduce FER by about two percentage points,” but they did not do so because those “seepage estimates have been challenged.”  Interestingly, many of the other studies NOAA researchers used to calculate emissions have also been challenged — so why is this study singled out?  By not accounting at all for natural seepage, those potentially massive amounts of naturally occurring methane were simply dropped into the natural gas production bucket, which doesn’t seem to be terribly scientifically rigorous.

The bottom line is that if the NOAA researchers had accounted for natural seepage, their conclusion would be that natural gas production leakage rates are below the threshold for natural gas to maintain its environmental benefits.

Fact #2: Methane emissions are rapidly declining

While the study was billed as stating that methane emissions from natural gas production are high and should be of great concern, when you dig into the data, it actually shows that methane emissions from natural gas production are “relatively low” and rapidly declining.  From the report:

“The decline in global FER is 0.1 and 0.3 percentage points per year since 1985 based on most likely (CH4 and δ13C−CH4 observations) and upper bound results (C2H6 observations), respectively. This assumes that the declines in measured C2H6 levels (or CH4 growth rates) are attributed to NG emissions reductions. Kirschke et al. find little if any long-term natural, agriculture/waste/landfill, and BBM emissions reductions over this period. Kirschke et al. results, along with the findings presented here, suggest that the declines in measured mixing ratios (or growth rates thereof) can be attributed to NG emissions reductions. This is also consistent with recent topdown C2H6 studies suggesting reductions in total FF emissions where Aydin et al. concluded that global declines in the C2H6 mixing ratios were due to decreased flaring and venting of NG (see also SI Figure S8). Also, recent direct CH4 measurements at 190 NG production sites in the U.S. by Allen et al.8 indicate lower overall CH4 emissions from production (well pad) activities than previous measurement data used in EPA’s 2013 GHG inventory.” (p. F)

The report goes on to explain that these reductions happened as natural gas production increased dramatically:

“Taking into account increasing NG (and other FF) production, the FER (in % of dry production) has been declining steadily over time.”  (p. G)

That’s doesn’t sound too bad at all.

Fact #3: Finds high emission estimates in some studies are not plausible nationwide

Greenwire called the report, “An even worse finding for the United States in terms of greenhouse gases is that some of its oil and gas fields are emitting more methane than the industry does, on average, in the rest of the world, the research suggests.” That article goes on to quote one of the lead researchers, Stefan Schweitzke, who said,

“I would have thought that emissions in the U.S. should be relatively low compared to the global average,” said Stefan Schwietzke, a researcher at the National Oceanic and Atmospheric Administration’s Earth Systems Research Laboratory in Boulder, Colo., and lead author of the studies. “It is an industrialized country, probably using good technology, so why are emissions so high?”

Oddly, that’s actually not what the report said.  The report is very clear that studies finding high leakage rates are not representative of emissions from natural gas production in the United States as a whole.  It even cites examples of the now infamous (and deeply flawed) Howarth and Ingraffea study as well as a recent NOAA study of the Uintah Basin in Utah as studies that are not representative of methane emissions from natural gas production nationwide.  From the report:

“Our most recent (2011) global upper bound of 4.4% FER suggests that two recent high estimates of 6−9% in the U.S. may be possible at individual sites, but do not appear representative of the national average unless U.S. NG industry practices are significantly worse than in the rest of the world.” (p. G; emphasis added)

The important question

To sum up: this latest NOAA study, by not addressing methane from natural petroleum seepage, is likely overestimating methane emissions from natural gas production. That’s not a flaw in the research, since it was acknowledged in the report repeatedly; it’s more of an example of how a scientific study can get misinterpreted within a media dynamic that’s looking for evidence of harm. Importantly, the study even admits that methane emissions from national gas production are rapidly declining as natural gas ramps up significantly, and that studies finding high leakage rates are not representative of emissions from the United States as a whole.

Overall, that’s not a bad picture, notwithstanding what the headlines might want you to believe.

The shale revolution, thus far, has been a North American phenomenon and American producers have made enormous strides adopting innovating technologies to reduce emissions.  The results are plain to see. The Environmental Protection Agency’s (EPA) latest Greenhouse Gas Inventory shows that methane emissions have dramatically decreased amid an unprecedented energy boom, and EPA attributes this decrease to voluntary efforts by producers to reduce emissions.  A study by the University of Texas and the Environmental Defense Fund found low methane emission rates from direct measurements of 190 different wells.

It could not be clearer methane emissions are being drastically reduced in the United States as natural gas production has soared. The fact that so much research confirms this should serve as a reminder, once again, that accusations of soaring methane leakage from shale wells are not firmly grounded in reality.

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