Articles | Volume 8, issue 2
Earth Syst. Dynam., 8, 235–253, 2017
Earth Syst. Dynam., 8, 235–253, 2017

Research article 10 Apr 2017

Research article | 10 Apr 2017

Accounting for the climate–carbon feedback in emission metrics

Thomas Gasser1,2,a, Glen P. Peters2, Jan S. Fuglestvedt2, William J. Collins3, Drew T. Shindell4, and Philippe Ciais1 Thomas Gasser et al.
  • 1Laboratoire des Sciences du Climat et de l'Environnement, LSCE/IPSL, Université Paris-Saclay, CEA – CNRS – UVSQ, 91191 Gif-sur-Yvette, France
  • 2Center for International Climate and Environmental Research – Oslo (CICERO), 0349 Oslo, Norway
  • 3Department of Meteorology, University of Reading, Reading, RG6 6BB, UK
  • 4Nicholas School of the Environment, Duke University, Durham, NC 27708, USA
  • anow at: International Institute for Applied Systems Analysis (IIASA), 2361 Laxenburg, Austria

Abstract. Most emission metrics have previously been inconsistently estimated by including the climate–carbon feedback for the reference gas (i.e. CO2) but not the other species (e.g. CH4). In the fifth assessment report of the IPCC, a first attempt was made to consistently account for the climate–carbon feedback in emission metrics. This attempt was based on only one study, and therefore the IPCC concluded that more research was needed. Here, we carry out this research. First, using the simple Earth system model OSCAR v2.2, we establish a new impulse response function for the climate–carbon feedback. Second, we use this impulse response function to provide new estimates for the two most common metrics: global warming potential (GWP) and global temperature-change potential (GTP). We find that, when the climate–carbon feedback is correctly accounted for, the emission metrics of non-CO2 species increase, but in most cases not as much as initially indicated by IPCC. We also find that, when the feedback is removed for both the reference and studied species, these relative metric values only have modest changes compared to when the feedback is included (absolute metrics change more markedly). Including or excluding the climate–carbon feedback ultimately depends on the user's goal, but consistency should be ensured in either case.

Short summary
Emission metrics such as GWP or GTP are used to put non-CO2 species on a CO2-equivalent scale. In the fifth IPCC report the metrics are inconsistent, as the climate–carbon feedback is included only for CO2 but not for non-CO2 species. Here, we simulate a new impulse response function for the feedback, and we use it to correct the metrics. For instance, 1 g of CH4 is equivalent to 31 g of CO2 (instead of 28 g) following the corrected GWP100 metric. It is 34 g if other factors are also updated.
Final-revised paper