Methane versus Carbon Dioxide: Mitigation Prospects

Authors: Alexander J. Severinsky, Allen L. Sessoms

Abstract:

Atmospheric carbon dioxide (CO2) has dominated the discussion around the causes of climate change. This is a reflection of a 100-year time horizon for all greenhouse gases that became a norm.  The 100-year time horizon is much too long – and yet, almost all mitigation efforts, including those set in the near-term frame of within 30 years, are still geared toward it. In this paper, we show that for a 30-year time horizon, methane (CH4) is the greenhouse gas whose radiative forcing exceeds that of CO2. In our analysis, we use the radiative forcing of greenhouse gases in the atmosphere, because they directly affect the rise in temperature on Earth. We found that in 2019, the radiative forcing (RF) of methane was ~2.5 W/m2 and that of carbon dioxide was ~2.1 W/m2. Under a business-as-usual (BAU) scenario until 2050, such forcing would be ~2.8 W/m2 and ~3.1 W/m2 respectively. There is a substantial spread in the data for anthropogenic and natural methane (CH4) emissions, along with natural gas, (which is primarily CH4), leakages from industrial production to consumption. For this reason, we estimate the minimum and maximum effects of a reduction of these leakages, and assume an effective immediate reduction by 80%. Such action may serve to reduce the annual radiative forcing of all CH4 emissions by ~15% to ~30%. This translates into a reduction of RF by 2050 from ~2.8 W/m2 to ~2.5 W/m2 in the case of the minimum effect that can be expected, and to ~2.15 W/m2 in the case of the maximum effort to reduce methane leakages. Under the BAU, we find that the RF of CO2 will increase from ~2.1 W/m2 now to ~3.1 W/m2 by 2050. We assume a linear reduction of 50% in anthropogenic emission over the course of the next 30 years, which would reduce the radiative forcing of CO2 from ~3.1 W/m2 to ~2.9 W/m2. In the case of "net zero," the other 50% of only anthropogenic CO2 emissions reduction would be limited to being either from sources of emissions or directly from the atmosphere. In this instance, the total reduction would be from ~3.1 W/m2 to ~2.7 W/m2, or ~0.4 W/m2. To achieve the same radiative forcing as in the scenario of maximum reduction of methane leakages of ~2.15 W/m2, an additional reduction of radiative forcing of CO2 would be approximately 2.7 -2.15 = 0.55 W/m2. In total, one would need to remove ~660 GT of CO2 from the atmosphere in order to match the maximum reduction of current methane leakages, and ~270 GT of CO2 from emitting sources, to reach "negative emissions". This amounts to over 900 GT of CO2.

Keywords: Methane Leakages, Methane Radiative Forcing, Methane Mitigation, Methane Net Zero.

References:

[1] Jeremy Deaton, Methane Levels Reach an All-Time High, New NOAA analysis highlights an alarming trend; experts call for curbing pollution from oil and gas wells., Nexus Media on April 12, 2020 in Scientific American, March 15-18, 2021 https://www.scientificamerican.com/article/methane-levels-reach-an-all-time-high/
[2] Center for Methane Research (CMR), 1700 S. Mount Prospect Rd. Des Plaines, Illinois 60018 www.gastechnology.org; Implications of Using Different GWP Time Horizons. https://www.gti.energy/wp-content/uploads/2019/02/CMR-Implications-Using-Different-GWP-Time-Horizons-White-Paper-2019.pdf
[3] International Gas Union, Understanding Methane Impact on Climate Change https://www.igu.org/app/uploads-wp/2017/10/IGU_17_002_Climate_Impacts_of_Methane_V3-7.pdf
[4] IPCC TAR-06, 2018, Chapter "Radiative Forces of Climate Change," pp. 352, 354 https://www.ipcc.ch/site/assets/uploads/2018/03/TAR-06.pdf
[5] Myhre, G., D. Shindell, F.-M. Bréon, W. Collins, J. Fuglestvedt, J. Huang, D. Koch, J.-F. Lamarque, D. Lee, B. Mendoza, T. Nakajima, A. Robock, G. Stephens, T. Takemura and H. Zhang, 2013: Anthropogenic and Natural Radiative Forcing. In: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)). Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA. https://archive.ipcc.ch/pdf/assessment-report/ar5/wg1/WG1AR5_Chapter08_FINAL.pdf
[6] James H. Butler, Stephen A. Montzka, The NOAA Annual Greenhouse Gas Index (AGGI), NOAA Earth System Research Laboratory, R/GMD, 325 Broadway, Boulder, CO 80305-3328, Updated Spring 2020. https://www.esrl.noaa.gov/gmd/aggi/aggi.html
[7] Etminan, M., G. Myhre, E. J. Highwood and K. P. Shine (2016), Radiative forcing of carbon dioxide, methane, and nitrous oxide: A significant revision of the methane radiative forcing, Geophys. Res. Lett., 43, 12,614–12,623, doi:10.1002/ 2016GL071930 https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL071930
[8] IEA, Sources of methane emissions, IEA, Paris, Last updated 26 August 2020 https://www.iea.org/data-and-statistics/charts/sources-of-methane-emissions-2
[9] Reuters, Joint effort announced to reduce emissions, Washington Post on November 23, 2017.
[10] Laura Feinstein, Eric de Place, Leaks in the City: Methane’s Invisible Menace, The surprising climate danger of “nonhazardous” natural gas leaks, Sightline Institute, April 23, 2020 https://www.sightline.org/2020/04/23/leaks-in-the-city-methanes-invisible-menace/
[11] Stephanie Paige Ogburn, How Much Natural Gas Leaks? Lost gas proves a slippery figure for scientists, industry and government, Scientific American, August 1, 2013. https://www.scientificamerican.com/article/how-much-natural-gas-leaks
[12] Shadia Nasralla, Satellites reveal major new gas industry methane leaks, ESG Environment, Reuters (London), June 25,2020. https://www.reuters.com/article/us-climatechange-methane-satellites-insi/satellites-reveal-major-new-gas-industry-methane-leaks-idUSKBN23W3K4
[13] Alex Kuffner, R.I. greenhouse-gas emissions rise 45% in new calculation of methane leaks, Providence Journal, September 12, 2019. https://www.providencejournal.com/news/20190912/ri-greenhouse-gas-emissions-rise-45-in-new-calculation-of-methane-leaks
[14] Real-Time and Historical CO2 Levels, Atmospheric CO2 Levels Graph, 2 oC Institute, last updated February 12, 2021. https://www.co2levels.org/
[15] Global Carbon Budget 2019v1.0 (2).xls; Global Carbon Project. (2019). Supplemental data of Global Carbom Budget. (2019) (Version 1.0) (Data set). Global carbon Project.
[16] https://doi.org/10.18160/gsp-2019; Integrated Carbon Observation System (ICOS). https://www.icos-cp.eu/science-and-impact/global-carbon-budget/2019
[17] Global Methane Budget, Highlights, Global Carbon Project 2001-2020 https://www.globalcarbonproject.org/methanebudget/20/hl-compact.htm The Global Methane Budget 2000–2017, Earth Syst. Sci. Data, 12, 1561–1623, 2020
[18] https://doi.org/10.5194/essd-12-1561-2020; © Author(s) 2020. This work is distributed under the Creative Commons Attribution 4.0 License. https://essd.copernicus.org/articles/12/1561/2020/
[19] Mufson S., BP, one of the world’s biggest oil-and-gas companies, says it is turning over a green leaf., The Washington Post, February 20, 2020; https://www.washingtonpost.com/climate-environment/2020/02/12/1a867124-4da4-11ea-bf44-f5043eb3918a_story.html
[20] Werner Aeschbach-Hertig at the University of Heidelberg, Clean Coal and Sparkling Water, Nature, Vol. 458, April 2, 2009