It is widely recognised that defining trade-offs between greenhouse gas emissions using emission equivalence based on global warming potentials (GWPs) referenced to carbon dioxide produces anomalous results when applied to methane. The short atmospheric lifetime of methane, compared to the timescales of CO2 uptake, leads to the greenhouse warming depending strongly on the temporal pattern of emission substitution.We argue that a more appropriate way to consider the relationship between the warming effects of methane and carbon dioxide is to define a mixed metric that compares ongoing methane emissions (or reductions) to one-off emissions (or reductions) of carbon dioxide.
Quantifying this approach, we proposed that a one-off sequestration of 1 t of carbon would offset an ongoing methane emission in the range 0.90-1.05 kg CH4 per year. We presented an example of how our approach would apply to rangeland cattle production, and consider the broader context of mitigation of climate change, noting the reverse trade-off would raise significant challenges in managing the risk of non-compliance.Our analysis was consistent with other approaches to addressing the criticisms of GWP-based emission equivalence, but provides a simpler and more robust approach while still achieving close equivalence of climate mitigation outcomes ranging over decadal to multi-century timescales.
For more related information, please see:
A.R. Lauder, I.G. Enting, J.O. Carter, N. Clisby, A.L. Cowie, B.K. Henry, M.R. Raupach, Offsetting methane emissions. An alternative to emission equivalence metrics, International Journal of Greenhouse Gas Control, Volume 12, January 2013, Pages 419-429, ISSN 1750-5836.http://www.sciencedirect.com/science/article/pii/S1750583612003064