Assessment of methane emissions from the U.S. oil and gas supply chain
A leaky endeavor
Considerable amounts of the greenhouse gas methane leak from the U.S. oil and natural gas supply chain. Alvarez et al. reassessed the magnitude of this leakage and found that in 2015, supply chain emissions were ∼60% higher than the U.S. Environmental Protection Agency inventory estimate. They suggest that this discrepancy exists because current inventory methods miss emissions that occur during abnormal operating conditions. These data, and the methodology used to obtain them, could improve and verify international inventories of greenhouse gases and provide a better understanding of mitigation efforts outlined by the Paris Agreement.
Science, this issue p. 186
Abstract
Methane emissions from the U.S. oil and natural gas supply chain were estimated by using ground-based, facility-scale measurements and validated with aircraft observations in areas accounting for ~30% of U.S. gas production. When scaled up nationally, our facility-based estimate of 2015 supply chain emissions is 13 ± 2 teragrams per year, equivalent to 2.3% of gross U.S. gas production. This value is ~60% higher than the U.S. Environmental Protection Agency inventory estimate, likely because existing inventory methods miss emissions released during abnormal operating conditions. Methane emissions of this magnitude, per unit of natural gas consumed, produce radiative forcing over a 20-year time horizon comparable to the CO2 from natural gas combustion. Substantial emission reductions are feasible through rapid detection of the root causes of high emissions and deployment of less failure-prone systems.
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Supplementary Material
Summary
Materials and Methods
Additional Author Disclosures
Figs. S1 to S11
Tables S1 to S12
Databases S1 and S2
Resources
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Information & Authors
Information
Published In
Science
Volume 361 • Issue 6398 • 13 July 2018
Pages: 186 - 188
History
Received: 19 December 2017
Accepted: 18 May 2018
21 June 2018
Copyright
Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.
This is an article distributed under the terms of the Science Journals Default License.
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Funding Information
http://dx.doi.org/10.13039/100000015U.S. Department of Energy: DE-FOA-0000894
http://dx.doi.org/10.13039/100000104National Aeronautics and Space Administration:
http://dx.doi.org/10.13039/100000192National Oceanic and Atmospheric Administration: NA14OAR0110139
http://dx.doi.org/10.13039/100000192National Oceanic and Atmospheric Administration: NA14OAR4310135
http://dx.doi.org/10.13039/100000879Alfred P. Sloan Foundation:
National Energy Technology Laboratory:
Fiona and Stan Druckenmiller:
Bill and Susan Oberndorf:
Betsy and Sam Reeves:
TomKat Charitable Trust:
http://dx.doi.org/10.13039/100010536Walton Family Foundation:
Robertson Foundation:
Heising-Simons Foundation:
RE: Natural gas as a bridge fuel to a carbon free future is still a myth
Alvarez et al. (1) summarized extensive measurements of methane emissions from oil and gas operations in the U.S. in 2015. They estimated emissions of 13 ± 2 Tg/y, equivalent to a mean of 2.3% of gross U.S. gas production. A national methane emission rate is fundamental to policy decisions concerning switching from other fossil fuels to natural gas. Previous work by Alvarez et al. (2) introduced the concept of technology warming potential (TWP) to relate emission rate to potential climate benefits from fuel switching for auto and truck transportation and for electricity generation.
Previously published (3) implications of fuel switching on climate benefit were based on estimates of emission rate and other factors needed to use the TWP approach. For example, new, high-efficiency natural gas power plants were shown to produce net climate benefits relative to efficient, new coal plants using low gassy coal on all time frames if leakage in the natural gas system is less than 2.7% from well through delivery at a power plant. Alvarez et al. did not update these implications in (1).
We have updated the TWP approach based on the new information provided in (1) and (4). Updated methane emission rates are normalized based on natural gas delivered to consumers in 2015, 25 Tcf (5), resulting in rates of 2.9% and 2.4% for well-to-pump and well-to-city gate, respectively.
Our analysis shows lower rates of emission are now required to show long-term climate benefits in all three sectors. The breakeven emission rate for coal switching is now about 2.2%: emission rates lower than these would result in immediate and long-term climate benefit. However, the current well-to-city gate emission rate of 2.4% is above this breakeven rate and would indicate a substantial delay in climate benefit. Moreover, for policy decisions it would be unwise to use a mean value for emission rate. Using a higher value to reflect uncertainty would further delay climate benefit.
Thus, the much-vaunted climate benefits of switching from coal to gas for power generation do not exist without substantial reductions in current upstream methane leakage, beyond the reductions in which the industry has already invested heavily. Moreover, while the industry has been trying to eliminate leakage sources in some instances, it is simultaneously and substantially increasing the volume of methane being mined, 20 Tcf in 2006, 25.2 TCF in 2016 (5), with concomitant increases in infrastructure and the number of potential leak sources.
Methane leakage makes natural gas a more climate damaging power generation source than coal over at least the first decade and a half of plant life. This updated analysis also confirms that switching from gasoline and diesel to compressed natural gas would benefit climate only if emission rate was substantially lower than that reported in (1). Natural gas as a bridge fuel to a carbon free future is a myth: the world does not have decades to wait to reduce usage of fossil fuels in transportation and power generation.
References:
1. Alvarez et al. Assessment of methane emissions from U.S. oil and gas supply chain. Science 186-188 (2018).
2. Alvarez et al. Greater focus needed on methane leakage from natural gas infrastructure. Proc. Natl. Acad. Sci. U.S.A. 109, 6435–6440 (2012).
3. http://blogs.edf.org/energyexchange/2013/11/05/methane-a-key-to-dealing-..., retrieved September 5, 2018.
4. Etminan et al. Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing. Geophys. Res. Lett. 43, 12614–12623 (2016).
5. EIA Natural Gas Consumption by End Use, retrieved September 5 2018, https://www.eia.gov/dnav/ng/ng_cons_sum_dcu_nus_a.htm.