Gas Technology Institute vs. Environmental Defense Fund: Who is Right About the Global Warming Potential of Methane Emissions from the Oil & Gas Industry?

Gas Technology Institute vs. Environmental Defense Fund: Who is Right About the Global Warming Potential of Methane Emissions from the Oil & Gas Industry? (Plus Insights from the GTI White Paper about Atmospheric Methane Trends)

A recently published Gas Technology Institute whitepaper attempts to quantify how much atmospheric methane contributes to radiative forcing and global warming. The sources used were the NOAA’s annual greenhouse gas index (AGGI), the Global Carbon Project (GCP), and the U.S. EPA. All are 2016 data. Their conclusions are that methane contributes to 16.7% of radiative forcing. They also conclude that roughly 52% of that is anthropogenic so that human activities produce about 8.8% of radiative forcing via methane. Fossil fuels, which include oil, gas, and coal contribute about 3.1% of radiative forcing. The U.S. natural gas industry, according to EPA numbers, contributed 1.2% of global methane emissions and therefore (16.7 x 0.012) = 0.2% of total radiative forcing. While this is still a lot of methane it is miniscule in terms of the total radiative forcing. Thus, when U.S. natural gas industry methane emissions are invoked as a major source of global warming this is generally overestimated. They are, however, a significant source of anthropogenic methane emissions. 1 unit out of 500 units does not constitute a major source. I unit out of 8 might. Regardless, it is still important to reign in methane emissions. The paper also notes that CO2 emissions are rising a lot faster relative to methane emissions so that the percentage of radiative forcing from methane relative to the total radiative forcing has been falling steadily and continues to do so. Thus, although methane emissions from natural gas are increasing due to more development their relative contribution to global warming has been steadily decreasing. The paper even utilized the more conservative (yielding higher emissions) “top-down” approach to emissions, which give contributions from fossil fuels a few tenths more percentage points than “bottom-up” approaches.

In terms of vastly increased U.S. natural gas production the emissions have not risen in tandem due to better recovery and less leakage. As the paper notes:

“Notably, despite the significant growth in U.S. natural gas production in recent years, studies by NOAA and others indicate that recent increases in atmospheric methane concentration are mainly from biological sources and less from fossil fuels.”

In late 2016 a paper came out in the American Geophysical Union that argued that due to “short-wave forcing” the 100-year global warming potential (GWP) of methane is actually 14% higher than the accepted IPCC value. If my math is correct that would mean that the U.S. natural gas industry might be responsible for 0.228 % rather than 0.200% of global radiative forcing. While that would be a slight increase it is not very significant in terms of the total. Greenhouse gas radiative forcing estimates are considered in general to have a 10% margin of error so there is considerable uncertainty. The short-wave effects for CO2 and nitrous oxide were within the margin of error while the methane was slightly beyond.

Illissa Ocko of the Environmental Defense Fund has argued that this change is significant enough to warrant more scrutiny. She notes in one article that atmospheric methane is responsible for about a quarter of the warming we are experiencing today. That is a bit misleading since historically methane was higher relative to CO2 and continues to drop relative to CO2 so that the contribution from methane  emissions today is about 16.7% and of that  just slightly more than half is anthropogenic. Even though the GWP of methane may well be very slightly underestimated the contribution from the U.S. natural gas industry it is still not a major source relative to the whole.

Ocko argues that there were three “misleading mistakes” in the GTI whitepaper. The first she calls ‘systematic undercounting.’ This involves methane’s heat-trapping effects via oxidation of methane to tropospheric ozone, stratispheric water vapor, and carbon dioxide – all of which also trap heat. These effects she says amount to about a third of methane’s heat-trapping effect. The mistake is made she says, by counting methane concentrations rather than total emissions – some of which is oxidized to the other heat-trapping gases. She cites an IPCC paper for this reasoning but there are significant uncertainties mentioned in the paper. The second mistake she notes is that anthropogenic methane emissions are underestimated in the GTI paper. Here she says that the GTI paper’s 8.8 % of methane emissions being anthropogenic is wrong and that it should be 25% - she may mean percentage of global anthropogenic methane emissions that come from global gas industries. She gives no evidence here – I think she could be referring to historical effects of methane on warming – which would be higher since methane was in the past higher relative to the total than it is now. Certainly, if natural sources of methane have remained constant over time, the “new” warming is mainly due to anthropogenic sources. One might then say that the anthropogenic portion of the total went from zero to the current percentage - her problem may be that the paper concentrates on percentage of total radiative forcing, natural plus anthropogenic. Certainly, the anthropogenic methane emitted is a higher percentage within the total anthropogenic greenhouse gases emitted or of the anthropogenic component of radiative forcing. Thus, she can argue that since there was natural methane before industrialization and other human impacts like expanded agriculture, that the anthropogenic impacts ids greater. The third mistake she argues is similar – that fossil fuel’s share of total methane emissions at 18.8% is also 30% of anthropogenic methane emissions. Thus, in terms of anthropogenic methane emissions she argues that the numbers are 3-4 times too low. It would have perhaps been better if the GTI paper would have included relative percentages of radiative forcing from anthropogenic-only sources. Below is the graph from the GTI paper showing relative percentages of the total:

Ocko also notes that:

“The fact is, methane emissions from the oil and gas sector represent the fastest, most cost-effective opportunity we have to slow global warming right now, in our lifetimes. Most of the solutions are already being deployed in some places, as they are simple and straightforward. Many pay for themselves in just a short time. All of them together will make a huge difference. The actual numbers prove the case.”

The bottom line is that depending how the data are presented neither is right or wrong but both emphasize biases. The GTI presentation as percentage of total global radiative forcing tends to reduce the impact of natural gas development. Presenting the data as percentage of total anthropogenic would probably have been better or both could have been presented. One might legitimately claim that the GTI's numbers have deliberately downplayed the impact of leaked methane since if you present the same data as percentages the anthropogenic methane emissions total the numbers suggest that the US natural gas industry is a significant (borderline major) source and that efforts to lower that amount can bear some fruit in terms of climate impacts. The percentage from US nat gas from the same data amounts to 13.6 % of the total of all anthropogenic methane sources and that is in radiative forcing. Graph below depicts those percentages. It is a sizable chunk of anthropogenic methane emissions. One might also present the data in terms of percentage of total anthropogenic greenhouse gas emissions which would give a lower amount. However, GTI's choice of using radiative forcing of oil & gas methane relative to all radiative forcing combined, both natural and anthropogenic, is inherently a trick of numbers although one needs to know those numbers as well. For example if pre-Industrial CO2 atmospheric concentrations were at 280ppm and are now at 410ppm that would mean that about 69% of the radiative forcing of CO2 is natural and 31% anthropogenic. In contrast, 52% of methane emissions are anthropogenic so a higher percentage of emitted methane is anthropogenic than emitted CO2. That means that comparing to the total emissions of all sources, natural and anthropogenic, will shrink the contribution from anthropogenic methane sources. It is a trick of number bias, but one it is good to keep in mind. Global warming detractors will often say that a mere 0.04% of our global atmosphere is composed of CO2. How could that possibly affect global climate? Well, it does it just as gradually by adding 0.003 deg C on avg. annually to the avg. global temperature - which has climbed about 0.5 deg C since the beginning of the Industrial Age (roughly and from my faulty memory). Thus, even small numbers can be significant over time. It's all a matter of perspective. The prevailing theory of climate change and global warming is a grand combinative effect based on both observation of the past and present and modeling of the future. There are significant uncertainties but many relative effects are reasonably understood. To recap US natural gas (by far the largest natural gas development and production system in the world) makes up 0.2% of total global radiative forcing but 13.6% of global anthropogenic methane radiative forcing according to the same data. Obviously, there is a big potential perceptive difference depending how the data is presented and work toward mitigating methane leakage should continue.

References:

Contributory Role of Atmospheric Methane and the Natural Gas Industry on Global Warming Radiative Forcing – by Gas Technology Institute – Center for Methane Research (2017)

Industry-Backed White Paper Low-Balls Oil & Gas Methane Impact – by Ilissa Ocko, in Environmental Defense Fund (blog), Feb. 28, 2018

Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing – by M. Etminan, G. Myhre, E. J. Highwood, K. P. Shine – in Geophysical Research Letters, Dec. 27, 2016

New science suggests methane packs more warming power than previously thought – by Ilisswa Ocko, in Environmental Defense Fund (blog), Feb. 7, 2018