Policy ForumSCI POLICY

Unmask temporal trade-offs in climate policy debates

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Science  05 May 2017:
Vol. 356, Issue 6337, pp. 492-493
DOI: 10.1126/science.aaj2350

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  • Unmask temporal trade-offs in climate policy debates: but how?
    • Katsumasa Tanaka, Senior Researcher, Center for Global Environmental Research, National Institute for Environmental Studies (NIES), Tsukuba, Japan
    • Other Contributors:
      • Francesco Cherubini, Professor, Industrial Ecology Programme, Department of Energy and Process Engineering, Norwegian University of Science and Technology
      • Annie Levasseur, Scientific Coordinator, CIRAIG, Department of Chemical Engineering, Polytechnique Montréal, Canada

    GWP100 is the most popular metric used to aggregate emissions of greenhouse gases on the common basis of CO2 for climate policies and assessments. The well-known limitations of using a single metric led to your proposal to combine application of GWP20 and GWP100 to address trade-offs between short- and long-term policy objectives (1). We support the proposal to adopt multiple metrics to better inform climate change impacts from different temporal perspectives. However, evidences suggest that both GWP20 and GWP100 are insufficient to capture long-term impacts (2), making such a proposal biased toward short-term.

    The Life Cycle Initiative under the UNEP/SETAC flagship project aimed to provide guidance for the use of emission metrics in climate impact analysis (3) based on the IPCC (4). While sharing the limitations of the single use of GWP100, it recommends a different combination (5, 6): GWP100 and GTP100. The GTP concept is more suited for the cost-effective climate stabilization stipulated in the UNFCCC (7). GWP100 numerically falls between GTP20 and GTP40 (2), indicating a time horizon of only 20 to 40 years under the climate stabilization framework. The use of GWP20 would imply an even shorter timeframe. The units of the impacts can be distinguished by using CH4 as the reference gas for near-term impacts, as opposed to long-term impacts measured in CO2-equivalents (8).

    Despite your drastic call for discarding alternative metrics (including GTP) based on th...

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    Competing Interests: None declared.