Evaluating global warming potentials with historical temperature: An application of ACC2 inversion
Tanaka, K., R. S. Tol, D. Rokityanskiy, B. C. O'Neill, and M. Obersteiner, 2008: Evaluating global warming potentials with historical temperature: An application of ACC2 inversion. IIASA Interim Report IR-07-035,.
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Global Warming Potentials (GWPs) are evaluated as historical temperature proxies by applying them to convert historical CH₄ and N₂O emissions to equivalent CO₂ emissions. Our GWP analysis is based on the inverse estimation for the Aggregated Carbon Cycle, Atmospheric Cycle, and Climate Model (ACC2). It was found that, for both CH₄ and N₂O, indices higher than the Kyoto GWPs (100-year time horizon) would reproduce better the historical temperature. The CH₄ GWP provides a best fit to the historical temperature with the time horizon of 44 years. However, the N₂O GWP does not approximate the historical temperature with any time horizon. We introduce a new exchange metric, TEMperature Proxy index (TEMP) that is defined so that it provides a best fit to the temperature projection of a given period. By comparing the GWPs and TEMPs, we found that the inability of the N₂O GWP to reproduce the historical temperature is caused by the fact that the GWP calculation methodology in IPCC gives coarse treatments to the background system dynamics and uncertain parameter estimations. Furthermore, our TEMP calculations demonstrate that indices have to be progressively updated upon the acquisition of new measurements and/or the advancement of our understanding on the Earth system processes.