Generated Summary
This research article, “Atmospheric methane removal: a research agenda,” explores the potential of atmospheric methane removal as a strategy to mitigate climate change. The study examines the technological aspects of methane removal, including energy requirements, and discusses various removal technologies such as photocatalysts, metal catalysts, and biological methods. It also addresses the impacts of methane removal on climate and air quality, emphasizing the need for a Methane Removal Model Intercomparison Project to quantify the expected impacts. The research aims to provide a comprehensive overview of the challenges and opportunities associated with methane removal, considering both the scientific and societal aspects. The work seeks to inform policy decisions and guide future research efforts in the field of climate change mitigation.
Key Findings & Statistics
- The average global increase of methane observed in 2020 was 14.7 ppb, the largest in the past four decades [1].
- Methane’s concentration has increased twice as fast as carbon dioxide (CO2) since 1750 and is now more than 2.5 times pre-industrial levels [1].
- Methane is the second most important anthropogenic greenhouse gas after CO2; the radiative forcings attributable to its direct (0.64 Wm-2) and direct-plus-indirect effects (0.97 W m−2) are 38% and 58%, respectively, of the 1.68 W m−2 for CO2 [2].
- Global methane emissions approached a record 600 Tg CH4 yr¯¹ in 2017, with anthropogenic sources contributing 61% of the total (approx. 365 Tg CH4 yr¯¹; [5–7]).
- The global total for 2017 was 50 Tg CH4 yr¯¹ more than the average for the period 2000–2006, primarily because anthropogenic emissions were 13% higher.
- Agriculture-related sources in 2017 contributed approximately two-thirds of global anthropogenic methane emissions (227 Tg CH4 yr¯¹) and fossil fuels contributed the other third (108 Tg CH4 yr-1) [5].
- Reaching zero methane emissions in global food production appears particularly unlikely this century.
- For rice farming, a meta-analysis of 52 studies found that non-continuous flooding reduced methane emissions by 53% on average compared to continuously flooded paddies.
- Methane emissions associated with the extraction, distribution, and use of fossil fuels grew by one-sixth from the early 2000s to 2017 [5,7].
- The minimum work of separation for methane in a generic process is nearly 33.5 kJ mol−¹ CH4.
- The minimum work of separation is 60% higher for methane than for CO2 in the atmosphere.
- With the same capture fraction of 70% and outlet purity of 97%, the minimum work of methane capture is 24 MJ/tCO2eq and 62 MJ/tCO2eq using GWP20 and GWP100, respectively.
- For CO2, the minimum work of capture is 459 MJ/tCO2, meaning that the minimum work of capture for the same radiative forcing impact is 7 times lower using methane’s GWP20 and 19 times lower using GWP100.
- The current best estimates of the expected relationship between methane and temperature include: a 40% reduction in methane emissions by 2050 is predicted to cause a temperature reduction of 0.3°C [95], whereas a 2% annual reduction in methane concentration is predicted to reduce temperature by 0.5°C by 2100 [96].
- For carbon dioxide, positive emissions lead to a temperature response of slightly different magnitude than for the same quantity of negative emissions [98].
Other Important Findings
- Because mitigating most anthropogenic emissions of methane is uncertain this century, and sudden methane releases from the Arctic or elsewhere cannot be excluded, technologies for methane removal or oxidation may be required.
- Carbon dioxide removal has an increasingly well-established research agenda and technological foundation, but no similar framework exists for methane removal.
- Technologies for methane removal include photocatalysts, metal catalysts associated with zeolites and porous polymer networks, biological methane removal, and iron-salt aerosol formation.
- The minimum energy per mole removed for a methane removal system is 60% higher than for a CO2 removal system.
- As the concentration of methane increases, the minimum work of separation decreases, emphasizing that addressing higher concentration sources first is desirable.
- Methane removal could also prove valuable for reducing peak temperatures, if it can be scaled sufficiently quickly.
Limitations Noted in the Document
- The study acknowledges the uncertainty in mitigating most anthropogenic emissions of methane and the potential for sudden methane releases.
- The research notes that there is no similar framework for methane removal as exists for carbon dioxide removal.
- The study highlights that the Methane Removal Model Intercomparison Project is needed to better quantify the expected impacts of methane removal.
- The research points out that the effectiveness of methane removal technologies at scale needs further investigation.
- The study mentions that climate and Earth-system impacts of methane removal require emissions-driven modeling to address.
- The document notes that the climate benefits of methane removal compared to those of CDR require a better understanding.
Conclusion
The study strongly advocates for a systematic research program focused on methane removal. It emphasizes that methane removal is a critical addition to existing methods of mitigating methane and carbon dioxide emissions. The potential benefits of methane removal include a reduction in the rate of global warming and a potential for lowering peak temperatures. The authors stress that the Methane Removal Model Intercomparison Project is essential to quantify the global and local impacts of methane removal. The study concludes by highlighting the importance of ongoing research and development to determine which approaches are most effective. It advocates for a comprehensive approach to studying methane removal, including technological innovation, modeling, and policy considerations. This research underscores the need to address methane emissions, not just as a standalone issue, but in the context of broader climate change mitigation strategies. The article highlights that the global warming potential of methane is much higher than CO2 in the short term, and if methane removal proves to be feasible at scale, it could provide advantages compared to CO2 mitigation in slowing the near-term rate of global warming. Overall, the research emphasizes the urgency and importance of methane removal as a crucial component of climate change mitigation efforts. It urges for the continued exploration and development of methane removal technologies as an essential part of global strategies to combat climate change and its potential effects.