The atmospheric lifetime of methane needs to be considered when designing policies to reduce emissions from ruminants – – © Ignacio Perez Dominguez

(Bilbao, 16 December, 2021)

Unlike the other main greenhouse gases (GHG) and particularly carbon dioxide (CO₂), methane (CH₄) has a short atmospheric life (around 10 years). Its warming effect is significant in the short term but diminishes in the long term. Depending on the time scale considered, methane’s contribution to agricultural emissions and climate change may vary substantially. This has important implications in the design of global climate change mitigation policies for agriculture.

Based on projections from three agricultural economic models, the paper shows how different valuations of methane, reflecting either a short- or long-term focus, may affect the cost-effectiveness of mitigation policies and the benefits of low-meat diets.

Emission metrics impact the choice of climate mitigation policies

Conventionally, the climate impact of a certain sector is evaluated through its annual greenhouse gas emissions, typically using the GWP100 metric, which estimates the change in atmospheric energy balance resulting from a GHG emission (i.e. Global Warming Potential) over a 100-year period. However, as GHG emissions are reported as CO₂-equivalents, GWP100 can fail to capture how the relative impacts of different gases change over time. Thus, the short-lived character of methane emissions has been arguably overlooked in most assessments of emission reductions required from the agricultural sector to achieve our climate targets. The study explores how different valuations of methane affect the ranking of mitigation policies in agriculture and, consequently, the sector’s contribution to global warming.

Mitigation policies focussed on methane’s short-term impact lead to greater emission reductions

The paper highlights that focussing specifically on the short-term effects of methane will lead to larger reductions of emissions compared to polices that do not consider methane’s short-liveness. Such stringent mitigation policies can even result in methane’s contribution to climate change dropping below current levels (since the warming effect of methane disappears). In this respect, decreasing methane emissions have the same overall effect as CO₂ uptake or carbon capture and storage technologies. Such policies will however have severe impacts on the agricultural sector in terms of prices and production.

Contribution of agricultural methane emissions to the overall temperature increase drops below current levels under stringent mitigation policies (CP500: carbon price of 500USD, LT: long term, ST: short term; CAPRI, GLOBIOM & MAGNET are the models used))

Low meat diets more effective under weaker agricultural emission reduction policy

The impact of low animal protein diets as a mitigation option strongly depends on the context in which it is occurring. If mitigation policies base themselves on metrics that reflect methane’s long-term behaviour (resulting in a lower relative valuation), methane emission intensity is not as greatly reduced by technical measures. Then, low meat diets appear as a more effective option to reduce emissions. If policies are less strict, reductions in meat consumption and consequently production in developed economies could therefore become an especially powerful mitigation mechanism.

Any reduction in global emissions from methane, as opposed to CO2, will lead to a rapid reduction in the level of methane in the atmosphere and thus to a reduction in the temperature associated with that concentration of atmospheric methane. Therefore, it is very important to report methane and CO2 separately and recognise a different treatment when designing climate mitigation policies. The Global Methane Pledge in the COP26 represents an important step in this direction, includes both biological and non-biological emissions (i.e. from Oil and Gas sectors), signed by more than 100 countries, aims to limit global methane emissions by 30% compared with 2020 levels. In any case, any reduction in biological methane emissions would bring an additional benefit to climate mitigation policies, but in no case it should replace urgent measures to decarbonize the economy.

A combination of innovative production-side mitigation measures and dietary changes in countries with high excess consumption per capita could achieve the most substantial effects in order to reverse the contribution of agriculture to global warming by reducing biological CH4 emissions.