19 Oct 2020
19 Oct 2020
Technical note: On comparing greenhouse gas emission metrics
- 1CSIRO Climate Science Centre, Oceans and Atmosphere, Aspendale, Vic, Australia
- 2Department of Mathematics, Swinburne University of Technology, PO Box 218, Hawthorn Vic, 3122, Australia
- 1CSIRO Climate Science Centre, Oceans and Atmosphere, Aspendale, Vic, Australia
- 2Department of Mathematics, Swinburne University of Technology, PO Box 218, Hawthorn Vic, 3122, Australia
Abstract. Many metrics for comparing greenhouse gas emissions can be expressed as an instantaneous Global Warming Potential multiplied by the ratio of airborne fractions calculated in various ways. The Forcing Equivalent Index (FEI) provides a specification for equal radiative forcing at all times at the expense of generally precluding point by point equivalence over time. The FEI can be expressed in terms of asymptotic airborne fractions for exponentially growing emissions. This provides a reference against which other metrics can be compared.
Four other equivalence metrics are evaluated in terms of how closely they match the timescale dependence of FEI, with methane, referenced to carbon dioxide, used as an example. The 100-year Global Warming Potential overestimates the long-term role of methane while metrics based on rates of change overestimate the short-term contribution. A recently-proposed metric, based on differences between methane emissions 20 years apart, provides a good compromise. Analysis of the timescale dependence of metrics, expressed as Laplace transforms leads to an alternative metric that gives closer agreement with FEI at the expense of considering methane over longer time periods.The short-term behaviour, which is important when metrics are used for emissions trading, is illustrated with simple examples for the four metrics.
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Ian Enting and Nathan Clisby


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RC1: 'Review of Technical Note by Enting and Clisby', Anonymous Referee #1, 17 Nov 2020
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RC2: 'Review of Enting and Clisby,', William Collins, 23 Nov 2020
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AC1: 'Comment on acp-2020-996: Author comment: General', Ian Enting, 05 Jan 2021
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AC2: 'Comment on acp-2020-996: Conclusions, restructured as suggested by reviewer 2', Ian Enting, 05 Jan 2021
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AC3: 'Comment on acp-2020-996: New section on practicality in use in response to reviewer 1.', Ian Enting, 05 Jan 2021
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AC4: 'Comment on acp-2020-996; Detailed response to reviewer 2', Ian Enting, 05 Jan 2021
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AC5: 'Comment on acp-2020-996: Detailed response to reviewer 1', Ian Enting, 06 Jan 2021
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AC6: 'Comment on acp-2020-996. Proposed appendix', Ian Enting, 11 Jan 2021


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RC1: 'Review of Technical Note by Enting and Clisby', Anonymous Referee #1, 17 Nov 2020
-
RC2: 'Review of Enting and Clisby,', William Collins, 23 Nov 2020
-
AC1: 'Comment on acp-2020-996: Author comment: General', Ian Enting, 05 Jan 2021
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AC2: 'Comment on acp-2020-996: Conclusions, restructured as suggested by reviewer 2', Ian Enting, 05 Jan 2021
-
AC3: 'Comment on acp-2020-996: New section on practicality in use in response to reviewer 1.', Ian Enting, 05 Jan 2021
-
AC4: 'Comment on acp-2020-996; Detailed response to reviewer 2', Ian Enting, 05 Jan 2021
-
AC5: 'Comment on acp-2020-996: Detailed response to reviewer 1', Ian Enting, 06 Jan 2021
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AC6: 'Comment on acp-2020-996. Proposed appendix', Ian Enting, 11 Jan 2021
Ian Enting and Nathan Clisby
Ian Enting and Nathan Clisby
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