Long-term climate change commitment and reversibility: an EMIC intercomparison

Zickfeld, Kirsten; Eby, Michael; Alexander, Kaitlin; Weaver, Andrew J.; Crespin, Elisabeth; Fichefet, Thierry; Goosse, Hugues; Philippon-Berthier, Gwenaëlle; Edwards, Neil R.; Holden, Philip B.; Eliseev, Alexey V.; Mokhov, Igor I.; Feulner, Georg; Kienert, Hendrik; Perrette, Mahé; Schneider von Deimling, Thomas; Forest, Chris E.; Friedlingstein, Pierre; Joos, Fortunat; Spahni, Renato; Steinacher, Marco; Kawamiya, Michio; Tachiiri, Kaoru; Kicklighter, David; Monier, Erwan; Schlosser, Adam; Sokolov, Andrei; Matsumoto, Katsumi; Tokos, Kathy S.; Olsen, Steffen M.; Pedersen, Jens O. P.; Ridgwell, Andy; Shaffer, Gary; Yoshimori, Masakazu; Zeng, Ning and Zhao, Fang (2013). Long-term climate change commitment and reversibility: an EMIC intercomparison. Journal of Climate, 26(6) pp. 5782–5809.

DOI: https://doi.org/10.1175/JCLI-D-12-00584.1

Abstract

This paper summarizes the results of an intercomparison project with Earth System Models of Intermediate Complexity (EMICs) undertaken in support of the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5). The focus is on long-term climate projections designed to: (i) quantify the climate change commitment of different radiative forcing trajectories, and (ii) explore the extent to which climate change is reversible on human timescales. All commitment simulations follow the four Representative Concentration Pathways (RCPs) and their extensions to 2300. Most EMICs simulate substantial surface air temperature and thermosteric sea level rise commitment following stabilization of the atmospheric composition at year-2300 levels. The meridional overturning circulation (MOC) is weakened temporarily and recovers to near pre-industrial values in most models for RCPs 2.6–6.0. The MOC weakening is more persistent for RCP 8.5. Elimination of anthropogenic CO2 emissions after 2300 results in slowly decreasing atmospheric CO2 concentrations. At year 3000 atmospheric CO2 is still at more than half its year-2300 level in all EMICs for RCPs 4.5–8.5. Surface air temperature remains constant or decreases slightly and thermosteric sea level rise continues for centuries after elimination of CO2 emissions in all EMICs. Restoration of atmospheric CO2 from RCP to pre-industrial levels over 100–1000 years requires large artificial removal of CO2 from the atmosphere and does not result in the simultaneous return to pre-industrial climate conditions, as surface air temperature and sea level response exhibit a substantial time lag relative to atmospheric CO2.

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