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New methane emissions metric proposed for climate change policy



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A new paper published today has outlined a better way to think about how methane and other gases contribute to greenhouse gas emissions budgets. This is an important step towards evaluating the warming from methane emissions when developing strategies to achieve the goals of the Paris Agreement.

“Current climate change policy suggests a ‘one size fits all’ approach to dealing with emissions,” says Professor Dave Frame, head of the Climate Change Research Institute at Victoria University of Wellington.  “But there are two distinct types of emissions, and to properly address climate change and create fair and accurate climate change policy we must treat these two groups differently.”

The two types of emissions that contribute to climate change can be divided into ‘long-lived’ and ‘short-lived’ pollutants.

“Long-lived pollutants, like carbon dioxide, persist in the atmosphere, building up over centuries. The CO2 created by burning coal in the 18th century is still affecting the climate today.” says Dr Michelle Cain from the Oxford Martin Programme on Climate Pollutants. “Short-lived pollutants, like methane, disappear within a few years. Their effect on the climate is important, but very different from that of CO2: yet current policies treat them all as ‘equivalent’”.

The research, which appears in the journal Nature Climate and Athmospheric Science, demonstrates a method of defining equivalence between the different emissions, which takes into account the lifetime effects. This would be particularly relevant to industries like agriculture, which contribute a large proportion of greenhouse gas emissions using traditional methods in some countries, for example New Zealand.

“We don’t actually need to give up eating meat to stabilise global temperatures,” says Professor Myles Allen who led the study (meat production is a major source of methane). “We just need to stop increasing our collective meat consumption. But we do need to give up dumping CO2 into the atmosphere. Every tonne of CO2 emitted is equivalent to a permanent increase in the methane emission rate. Climate policies could be designed to reflect this.”

 “Under current policies, industries that produce methane are managed as though that methane has a permanently worsening effect on the climate,” says Professor Frame. “But this is not the case. Implementing a policy that better reflects the actual impact of different pollutants on global temperatures would give agriculture a fair and reasonable way to manage their emissions and reduce their impact on the environment.”

 “Implementing a policy like this would show New Zealand to be leaders and innovators in climate change policy,” says Professor Allen. “Implemented successfully, it could also completely stop New Zealand’s contribution to global warming.”

The work, which is a collaboration between researchers at Victoria University of Wellington, the Universities of Oxford and Reading, and the Centre for International Climate Research in Norway (CICERO), shows a better way to think about how methane might fit into carbon budgets.

The paper is freely available at: Allen, M. R., Shine, K. P., Fuglestvedt, J. S., Millar, R. J., Cain, M., Frame, D. J., & Macey, A. H. (2018). A solution to the misrepresentations of CO2-equivalent emissions of short-lived climate pollutants under ambitious mitigation. Npj Climate and Atmospheric Science, 1(1), 16. https://doi.org/10.1038/s41612-018-0026-8

Further reading;  “Climate metrics under ambitious mitigation”.

Watch our interivew with Dr Michelle Cain, discussing the motivation for the research, the use of the proposed metric, GWP*, and how it will enable people to assess emission reductions in relation to the long term temperature goal.