Balancing methane emissions with short-term removal reveals how big of a problem we have

It has been suggested (Höglund, 2023) that short-term storage could be used to balance out short-lived greenhouse gas emissions. At first sight, this seems very practical. Carbon storage that lasts about a decade would be perfectly matched to cancel out methane (CH₄) emissions. By the time the storage releases the carbon back into the environment, the methane would have decayed away. The focus on methane avoids getting into arguments over how long the storage needs to last. Conceptually, this approach is clean. It also clarifies that methane management and carbon management are best handled separately. From a carbon management perspective and to combat the long-term warming effect, every ton of carbon released into the environment should be canceled with a ton of carbon stored permanently. This would cancel out carbon dioxide (CO₂) emissions and account for the long-term impact of CH₄, which will gradually convert to CO₂.

From a methane management point of view, short-term storage of the right duration fits the mitigation of the excess radiative forcing of methane very well. If the CO₂ and CH₄ accounting schemes are kept apart, then this works well. However, from a practical perspective, this shows how big the greenhouse gas problem really is. Anthropogenic methane emissions from all sources add to about 380 Mt/year (Jackson 2019). Since the radiative forcing per tonne of methane is roughly 100 times stronger than that of a tonne of CO₂(by weight), one would need to store about 100 tonnes of CO₂ to compensate for the emission of 1 tonne of methane. In other words, one would have to aim for 38 Gt of CO₂ removal per year and store it on a decadal time scale. That far exceeds current storage activities, but it would only address methane emissions. But it is not too surprising. As the Intergovernmental Panel on Climate Changenoted, the instant contribution of methane to the warming is quite large. Methane is important as today’s methane emissions contribute instantly as much to global warming as today’s CO₂ emissions. However, CO₂ emissions from 20 years ago are still contributing to today’s warming, whereas the methane emitted back then is long gone. Not letting temporary storage pretend that it takes care of long-term greenhouse warming makes it clear that the short-term storage capacity is likely insufficient ^[1,2] to solve the methane problem. A better focus would be on eliminating methane emissions.

Notes

^[1] Griscom et al. (2017) estimate 23 GtCO₂-eq carbon stored and avoided from nature-based conservation, restoration, and improved land management is the maximum potential when constrained by food, fiber, and biodiversity. The inclusion of avoided emissions and non-CO₂ gases indicated the maximum storage potential from short term removal would be smaller.  

^[2] Fuss et al. (2018) reports a maximum potential of 0.5-3.6 GtCO₂ from afforestation and reforestation, which are only a subset of the full range of nature based pathways possible.

Work cited

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Griscom, B.W., Adams, J., Ellis, P.W., Houghton, R.A., Lomax, G., Miteva, D.A., Schlesinger, W.H., Shoch, D., Siikamäki, J.V., Smith, P., Woodbury, P., Zganjar, C., Blackman, A., Campari, J., Conant, R.T., Delgado, C., Elias, P., Gopalakrishna, T., Hamsik, M.R., Herrero, M., Kiesecker, J., Landis, E., Laestadius, L., Leavitt, S.M., Minnemeyer, S., Polasky, S., Potapov, P., Putz, F.E., Sanderman, J., Silvius, M., Wollenberg, E., Fargione, J., 2017. Natural climate solutions. Proceedings of the National Academy of Sciences of the United States of America 114, 11645–11650. https://doi.org/10.1073/pnas.1710465114

Höglund, R. How much carbon will we need to remove? Medium. 2023 Sep 4. https://roberthoglund.medium.com/how-much-carbon-will-we-need-to-remove-26fda7b5e19a

Jackson RB, Saunois M, Bousquet P, Canadell JG, Poulter B, Stavert AR, Bergamaschi P, Niwa Y, Segers A, Tsuruta A. Increasing anthropogenic methane emissions arise equally from agricultural and fossil fuel sources. Environmental Research Letters. 2020 Jul 15;15(7):071002.