May-2022

Delivering the Global Methane Pledge

Atmospheric methane concentrations have risen by almost 10% in the past 20 years, so how do we deliver a 30% reduction in methane emissions by 2030?

Robin Nelson
Consulting Editor

Article Summary

The first half of our extended feature on the Global Methane Pledge summarises the commitment to a 30% reduction in global methane emissions by 2030. We consider natural methane sources and sinks and the impact of anthropogenic methane emissions. We summarise the major initiatives and technologies available for reducing emissions from agriculture and waste by 2030. Opportunities for the energy sector to collect and use methane from anaerobic digesters or avoid methane emissions from waste by investing in waste-to-fuels and waste-to-plastics processes are highlighted. The second half focuses on initiatives to reduce methane emissions from the oil and gas supply chain.

What is the Global Methane Pledge?
- In November 2021, the US and the EU jointly announced the Global Methane Pledge, a global partnership with over 100 countries, which could avert 0.2°C of global warming by 2050 (US Department of State, 2021a).

- Countries joining the Global Methane Pledge commit to a collective goal of reducing global methane emissions by at least 30% from 2020 levels by 2030 and moving towards the best available inventory methodologies to quantify methane emissions, focusing on high emission sources (European Commission, 2021).

- The Global Methane Pledge was supplemented by a separate US-China cooperation agreement to develop additional measures to enhance methane emission control before COP27. China intends to develop a comprehensive and ambitious National Action Plan on methane, aiming to significantly affect methane emissions control and reductions in the 2020s (US Department of State, 2021b).

Atmospheric methane concentrations
Atmospheric concentrations of methane (CH4) averaged about 500 ppb (see Figure 1, left) for hundreds of thousands of years but, with the onset of industrialisation, increased to over 1800 ppb by 2019 (see Figure 1, right, EPA, 2021a). Although these concentrations are at least an order of magnitude lower than carbon dioxide (CO2), the global warming potential of methane over 100 years (GWP100) is 28-36 that of CO2.

Natural sources of methane
Methane is formed biogenically as a result of anaerobic decomposition of organic matter in wetlands and forests.

Over time, substantial deposits of natural gas, primarily methane but with lesser amounts of ethane (C2H6), propane (C3H8), butane (C4H10), and pentane (C5H12), have formed from thermogenic decomposition in underground rock formations under the surface of the Earth, often in association with other hydrocarbon reservoirs including coal and oil. Methane hydrates occur in oceanic sediments as methane clathrate (CH4)4(H20)23. Methane can be released naturally from these deposits (Skarke et al., 2014).

Methane is also formed pyrogenically by the combustion of biomass, for example, from forest fires caused by lightning strikes.

Natural methane sinks, such as the reaction with hydroxyl (OH-) radicals within the troposphere, oxidation by methanotrophic bacteria and other chemical reactions with oxygen and free chlorine in the atmosphere, maintained an equilibrium with natural methane emissions (IPIECA, 2021a). By 2017, natural sources only accounted for 39% of global methane emissions (see Figure 2).

Anthropogenic emissions of methane
Anthropogenic emissions reached 62% of global methane emissions, or 1.6 times the natural emissions by 2017, while methane sinks removed an estimated 96% of total (natural and anthropogenic) emissions (Global Carbon Atlas, 2020). Anthropogenic emissions are considered the main cause of higher atmospheric methane concentrations, although changes impacting the flux between emissions and sinks may also be a factor.

Globally, the main anthropogenic sources are agriculture at 45%, followed by fossil fuel production and use (coal, oil, and natural gas) at 24%, waste at 20%, and smaller amounts from burning of biomass and biofuels, residential, and industrial emissions (see Figure 2). However, the ranking of anthropogenic emissions changes in different regions of the world. Emissions from paddy fields reflect the importance of rice cultivation in Asia. Similarly, the increased reliance on coal for power in Asia results in a higher contribution from coal relative to oil and gas, whereas in Europe, rice and coal rank lower than emissions from livestock and gas (Saunois, et al., 2020).

Reducing methane emissions from  agriculture and waste
The UN Climate and Clean Air Coalition (CCAC) estimates that known techniques and management practices could reduce emissions by between 21 and 40% of that needed for agriculture to contribute to its share of methane emissions reductions. Farmers will readily adopt new practices if they can realise tangible benefits in terms of greater productivity, lower input costs, or more sustainable yields through better resource management. The UN International Methane Observatory in its theory of change aims to catalyse action by plant managers (IMEO, 2021a). Whilst this comment is in relation to emissions from oil and gas operations, it is equally valid, but with less global governance, more problematic, in the context of reducing methane from agriculture.