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Earth System Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 9, issue 3 | Copyright
Earth Syst. Dynam., 9, 1013-1024, 2018
https://doi.org/10.5194/esd-9-1013-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 17 Aug 2018

Research article | 17 Aug 2018

A quantitative approach to evaluating the GWP timescale through implicit discount rates

Marcus C. Sarofim1 and Michael R. Giordano2 Marcus C. Sarofim and Michael R. Giordano
  • 1Climate Change Division, US Environmental Protection Agency, Washington, DC 20001, USA
  • 2AAAS S&T Policy Fellow Hosted by the EPA Office of Atmospheric Programs, Washington, DC 20001, USA

Abstract. The 100-year global warming potential (GWP) is the primary metric used to compare the climate impacts of emissions of different greenhouse gases (GHGs). The GWP relies on radiative forcing rather than damages, assumes constant future concentrations, and integrates over a timescale of 100 years without discounting; these choices lead to a metric that is transparent and simple to calculate, but have also been criticized. In this paper, we take a quantitative approach to evaluating the choice of time horizon, accounting for many of these complicating factors. By calculating an equivalent GWP timescale based on discounted damages resulting from CH4 and CO2 pulses, we show that a 100-year timescale is consistent with a discount rate of 3.3% (interquartile range of 2.7% to 4.1% in a sensitivity analysis). This range of discount rates is consistent with those often considered for climate impact analyses. With increasing discount rates, equivalent timescales decrease. We recognize the limitations of evaluating metrics by relying only on climate impact equivalencies without consideration of the economic and political implications of metric implementation.

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The 100-year GWP is the most widely used metric for comparing the climate impact of different gases such as methane and carbon dioxide. However, there have been recent arguments for the use of different timescales. This paper uses straightforward estimates of future damages to quantitatively determine the appropriate timescale as a function of how society discounts the future and finds that the 100-year timescale is consistent with commonly used discount rates.
The 100-year GWP is the most widely used metric for comparing the climate impact of different...
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