Scientists’ Statement on Lowering Atmospheric Methane Concentrations

Afficher en français

Anzeige in Deutsch

April 16, 2021

We the undersigned scientists whose expertise includes atmospheric chemistry, climate change, and related fields, concerned by rapidly rising atmospheric methane concentrations, call on national and global leaders to take effective measures to cut methane emissions, reduce atmospheric methane concentrations, and return methane in the atmosphere to preindustrial levels.

Currently, atmospheric methane concentrations are at a record high, about 2.5 times higher than the preindustrial level of ~750 parts per billion, and continue to rise rapidly. A particularly sharp rise in atmospheric methane has been underway since 2007, including the largest annual growth on observational record in 2020 despite the pandemic.[1] This may be attributable to a variety of factors, ranging from biological sources[2] to previously underestimated fugitive methane from the fossil fuel industry.[3]  Whatever the causes, the Paris Climate Agreement[4] did not anticipate the sharp rise in methane.  Nor do the pathways the IPCC laid out for keeping global warming to 1.5 °C[5] take it into account.[6]^,[7]

The pre-industrial level of CO₂ equivalent (CO₂e) in the atmosphere (including all greenhouse gases) was 320 parts per million (ppm);  today it is over 500 ppm.  Using the common convention of citing CO₂ alone, the atmospheric concentration is 415 ppm, but that ignores rising concentrations of methane and other non-CO₂ climate pollutants.  We strongly urge using CO₂ equivalent as a fairer indicator of climate forcing.

Methane is a potent warming agent (84 times more powerful than CO₂ over 20 years).[8]   Atmospheric methane accounts for roughly 25% of the radiative forcing driving climate change.[9]  Lowering atmospheric methane concentrations is therefore important for avoiding catastrophic climate change, and must be part of any effective strategy for meeting climate goals.

As the planet warms, scientists are seeing signs of acceleration in localized natural methane emissions in the Arctic. For example in October 2019, an international team of mainly Russian scientists observed firsthand bucket-sized methane bubbles rising through the ocean from seabed permafrost melting below the East Siberian Sea.[10] The same team had observed steadily increasing emissions of such gas plumes in annual expeditions since 2008.[11]  Methane releases are also forming craters in the permafrost. Seventeen large craters from methane explosions have appeared on the Yamal Peninsula since 2014. One was observed directly by scientists in 2020.[12] While emissions from such sources are still small compared to natural methane sources globally, more monitoring is needed to know how methane emissions in the Arctic are developing regionally and over time.  

Many nations including the United States are adopting strategies for reducing or mitigating anthropogenic methane emissions at their sources. These measures are critically important. They may include capping oil and gas wells and stopping other fugitive methane emissions from the fossil fuel industry, decarbonizing and managing demand for energy, addressing agricultural emissions, and managing demand for methane-intensive products.[13]

In addition to mitigating or reducing the emissions of climate pollution, we also recognize the need to reduce concentrations of climate forcing agents already in the atmosphere, including methane.  Intractable methane emissions that are hard or impossible to mitigate nevertheless need to be addressed in order to bring atmospheric methane concentrations down to safe levels.  Anthropogenic sources currently account for 50-60% of all methane emissions[14] and rising, not all of which are susceptible to mitigation. Methane emissions from natural sources are also accelerating as the planet warms.  Anthropogenic and biogenic emissions overlap, since human-caused climate change is driving them both. To deal with methane emissions that can’t otherwise be mitigated, to reduce the overall methane burden, and to get atmospheric methane levels to a range consistent with meeting climate goals, we must combine prevention and mitigation of new methane emissions with actively lowering the concentration of methane already in the atmosphere.   

Research is currently underway on scalable methods that can accelerate and enhance atmospheric methane oxidation (a naturally occurring process which continuously removes methane from the atmosphere),[15]^,[16] such that it could become sufficient to lower atmospheric methane concentrations even as natural methane emissions and some anthropogenic emissions continue to rise.  Given adequate funding for research and development and testing, it should be possible to rapidly develop safe and effective enhanced atmospheric methane oxidation technologies and infrastructure.   

When combined with aggressive mitigation of methane emissions, these technologies have the potential to reduce atmospheric methane concentrations rapidly and substantially. The stakes of realizing this potential are high, and the opportunity is great. For example, cutting atmospheric methane concentrations in half would return radiative forcing from greenhouse gases to 2005 levels,[17] complementing other forms of climate action and helping significantly to put ambitious climate goals within reach.[18]^,[19]  

At the same time, it would have significant co-benefits. The social cost of methane per ton is an order of magnitude higher than that of CO₂.[20]  Methane triggers ozone (O₃) formation in the troposphere, which damages human health and agricultural harvests. Reducing atmospheric methane would also reduce these impacts.

As such, lowering atmospheric methane concentrations is an additional, reinforcing action that should be considered a necessary component of an effective climate strategy.  We therefore urge national and global leaders to:

1). ensure that all countries are committed to aggressively reducing or mitigating methane emissions at their sources;

2). fund and initiate programs to monitor atmospheric methane and to research and develop technologies that reduce atmospheric methane safely and effectively; and

3). frame and implement a global agreement to return atmospheric methane concentrations to preindustrial levels.

Signed:

United Kingdom

United States

France

Canada

Japan

Germany

---

[1] https://research.noaa.gov/article/ArtMID/587/ArticleID/2742/Despite-pandemic-shutdowns-carbon-dioxide-and-methane-surged-in-2020 “NOAA’s preliminary analysis showed the annual increase in atmospheric methane for 2020 was 14.7 parts per billion (ppb), which is the largest annual increase recorded since systematic measurements began in 1983. The global average burden of methane for December 2020, the last month for which data has been analyzed, was 1892.3 ppb. That would represent an increase of about 119 ppb, or 6 percent, since 2000.”

[2] Nisbet, E. G., et al. (2016). Rising atmospheric methane: 2007–2014 growth and isotopic shift, Global Biogeochem. Cycles, 30, 1356– 1370, doi:10.1002/2016GB005406.

[3] Schwietzke, S., Sherwood, O., Bruhwiler, L. et al. (2016). Upward revision of global fossil fuel methane emissions based on isotope database. Nature 538, 88–91. https://doi.org/10.1038/nature19797

[4] The English text of the Paris Agreement can be found here: https://unfccc.int/sites/default/files/english_paris_agreement.pdf.

[5] Hansen, J., et al. (2017). Young people’s burden: requirement of negative CO2 emissions. Earth System Dynamics, 8(3), 577-616. https://doi.org/10.5194/esd-8-577-2017

[6] Nisbet, E. G., et al. (2019). Very strong atmospheric methane growth in the 4 years 2014–2017: Implications for the Paris Agreement. Global Biogeochemical Cycles, 33(3), 318-342. https://doi.org/10.1029/2018GB006009

[7] Ganesan, A. L., Schwietzke, S., Poulter, B., Arnold, T., Lan, X., Rigby, M., et al. (2019). Advancing scientific understanding of the global methane budget in support of the Paris Agreement. Global Biogeochemical Cycles, 33, 1475-1512. https://doi.org/10.1029/2018GB006065   “Since the Paris Agreement, CH₄ mole fractions in the atmosphere have, however, increased above the RCP2.6 pathway (Figure 2a). In 2018, CH₄ mole fractions were more than 100 ppb higher than in RCP2.6 and were also higher than RCP4.5 (Nisbet et al., 2019). While RCP2.6 is only intended to be indicative of scenarios that keep below 2 °C, it shows a divergence in radiative forcing that has been larger for CH₄ than for CO₂ and nitrous oxide (Figure 2b, Nisbet et al., 2019).” 

[8] Intergovernmental Panel on Climate Change. (2014). Myhre, G., D. et al. (Eds). Anthropogenic and Natural Radiative Forcing. In Climate Change 2013 – The Physical Science Basis: Working Group I Contribution to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change (pp. 659-740). Cambridge: Cambridge University Press. https://doi.org/10.1017/CBO9781107415324.018 . Retrieved December 18, 2020.

[9] Ganesan, et al., 2019. 

[10] https://www.cnn.com/2019/10/12/us/arctic-methane-gas-flare-trnd/index.html

[11] Wadhams, P. (2016). A Farewell to Ice. Allen Lane, Ch. 9.

[12] Bogoyavlensky, Vasily; Bogoyavlensky, Igor; Nikonov, Roman; Kargina, Tatiana; Chuvilin, Evgeny; Bukhanov, Boris; Umnikov, Andrey. (2021). “New Catastrophic Gas Blowout and Giant Crater on the Yamal Peninsula in 2020: Results of the Expedition and Data Processing” Geosciences 11, no. 2: 71. https://doi.org/10.3390/geosciences11020071

[13] Harmsen, M., van Vuuren, D.P., Bodirsky, B.L. et al. (2020). The role of methane in future climate strategies: mitigation potentials and climate impacts. Climatic Change 163, 1409–1425. https://doi.org/10.1007/s10584-019-02437-2

[14] Saunois M et al. (2020). “The Global Methane Budget” 2000-2017. Earth System Science Data 12:1561-1623.  https://essd.copernicus.org/articles/12/1561/2020/

[15] Nisbet, E. G., Fisher, R. E., Lowry, D., France, J. L., Allen, G., Bakkaloglu, S., et al. (2020). Methane mitigation: methods to reduce emissions, on the path to the Paris agreement. Reviews of Geophysics, 58, e2019RG000675. https://doi.org/10.1029/2019RG000675

[16] Boucher, O., and Folberth, G.A., (2010) “New directions: atmospheric methane removal as a way to mitigate climate change?.” Atmospheric environment 44(27), 3343-3345. https://doi.org/10.1016/j.atmosenv.2010.04.032

[17] For the basis of this calculation, see https://www.esrl.noaa.gov/gmd/aggi/aggi.html . Halving methane levels would reduce methane forcing by round 80%, bringing it down by 0.413. If this is subtracted from the total, the total forcing becomes 1.66, which corresponds to the year 2005.

[18] Jackson, R.B., Solomon, E.I., Canadell, J.G. et al. (2019). Methane removal and atmospheric restoration. Nat Sustain 2, 436–438. https://doi.org/10.1038/s41893-019-0299-x

[19] de Richter, R., Ming, T., Davies, P., Liu, W., & Caillol, S. (2017). Removal of non-CO2 greenhouse gases by large-scale atmospheric solar photocatalysis. Progress in Energy and Combustion Science, 60, 68-96. https://doi.org/10.1016/j.pecs.2017.01.001

[20] Interagency Working Group on Social Cost of Greenhouse Gases (IWG). (2021). Technical Support Document: Social Cost of Carbon, Methane, and Nitrous Oxide Interim Estimates under Executive Order 13990. February.  Available at:  https://www.whitehouse.gov/wp-content/uploads/2021/02/TechnicalSupportDocument_SocialCostofCarbonMethaneNitrousOxide.pdf