How the way we measure the effects of methane matters for climate policy

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 study just published in the journal Nature Food 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. The global economy wide MAGNET model of Wageningen Research is on of the core models.

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 Global Warming Potential over a 100 year period metric  ̶  GWP100  ̶  which estimates the change in atmospheric energy balance resulting from a particular type of GHG emission. However, as GHG emissions are reported as CO₂-equivalents, GWP100 can fail to capture how the relative impacts of different gases change over time.

“The short-lived character of methane emissions has been arguably overlooked in most assessments of emission reductions required from the agricultural sector to achieve climate targets,” explains co-author Hans van Meijl, the scientific coordinator of Wageningen Economic Research. “The methane specificities – by which we mean a significant warming effect and related mitigation potential in the short term and the “climate neutrality” of a stable level of emissions in the long term – deserve distinct treatment in climate mitigation policies. This has been also recognized in the Global Methane Pledge, announced by the US and the EU and supported by more than 100 countries, which represents a commitment to reduce,  particularly global methane emissions by at least 30% from 2020 levels by 2030.” In this study we explored 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 findings indicate that mitigation policies focused on methane’s short-term impact lead to greater emission reductions and the authors highlight that focusing specifically on the short-term effects of methane will lead to larger reductions of emissions compared to policies 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. 

In a News and Views article of this study Jan Peter Lesschen (2021) of Wageningen Environmental Research stresses that “Although the IPCC Sixth Assessment Report recognizes this issue, it does not recommend the use of one specific emission metric, as the choice depends on the purposes for which GHGs are being compared. Thus, the choice of a metric is largely a political decision as it depends on which aspects of climate change are considered most important to a particular application or stakeholder over a given time horizon. The use of the GWP* metric, which better reflects the short-term lifetime of methane, would be advantageous at the global level to better represent the impact of methane on global temperature and for the design of mitigation strategies, but not yet for reporting purposes at the national or product levels. Scenario studies, such as that presented by Pérez-Domínguez and colleagues, can inform this discussion by showing the impact of different metrics and mitigation policies.”

Low meat diets are more effective under weaker agricultural emission reduction policy

The authors further highlight that 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 behavior (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.

A combination of innovative production-side policy measures worldwide and dietary changes in countries with high calorie consumption per capita could achieve the most substantial emission reduction levels, helping to significantly reverse the contribution of agriculture to global warming.