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Climate change under aggressive mitigation: the ENSEMBLES multi-model experiment |
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| Authors: | T C Johns J-F Royer I H?schel H Huebener E Roeckner E Manzini W May J-L Dufresne O H Otter? D P van Vuuren D Salas y Melia M A Giorgetta S Denvil S Yang P G Fogli J K?rper J F Tjiputra E Stehfest C D Hewitt |
| Institution: | 1. Hadley Centre, Met Office, FitzRoy Road, Exeter, EX1 3PB, UK 2. Centre National de Recherches M??t??orologiques-Groupe d??Etude de l??Atmosph??re M??t??orologique (CNRM-GAME Meteo-France CNRS), 42 Avenue G. Coriolis, 31057, Toulouse, France 3. Institute for Meteorology, Freie Universit?t Berlin, Carl-Heinrich-Becker-Weg 6-10, 12165, Berlin, Germany 4. Hessian Agency for the Environment and Geology, Rheingaustra?e 186, 65203, Wiesbaden, Germany 5. Max Planck Institute for Meteorology, Bundesstrasse 53, 20146, Hamburg, Germany 6. Istituto Nazionale di Geofisica e Vulcanologia, Bologna, Italy 7. Centro Euro-Mediterraneo per i Cambiamenti Climatici (CMCC), Bologna, Italy 8. Danish Climate Centre, Danish Meteorological Institute, Lyngbyvej 100, 2100, Copenhagen, Denmark 9. UMR 8539 CNRS, ENS, UPMC, Ecole Polytechnique, Laboratoire de M??t??orologie Dynamique (LMD/IPSL), 75252, Paris Cedex 05, France 10. Nansen Environmental and Remote Sensing Center, Thorm?hlensgt. 47, 5006, Bergen, Norway 11. Bjerknes Centre for Climate Research, Allegt. 55, 5007, Bergen, Norway 16. Uni. Bjerknes Centre, Allegt. 55, 5007, Bergen, Norway 12. Planbureau voor de Leefomgeving (PBL), Bilthoven, The Netherlands 15. Utrecht University, Utrecht, The Netherlands 13. FR 636 CNRS, UVSQ, UPMC, Institut Pierre Simon Laplace (IPSL), 75252, Paris Cedex 05, France 14. Department of Geophysics, University of Bergen, Allegt. 70, 5007, Bergen, Norway |
| Abstract: | We present results from multiple comprehensive models used to simulate an aggressive mitigation scenario based on detailed results of an Integrated Assessment Model. The experiment employs ten global climate and Earth System models (GCMs and ESMs) and pioneers elements of the long-term experimental design for the forthcoming 5th Intergovernmental Panel on Climate Change assessment. Atmospheric carbon-dioxide concentrations pathways rather than carbon emissions are specified in all models, including five ESMs that contain interactive carbon cycles. Specified forcings also include minor greenhouse gas concentration pathways, ozone concentration, aerosols (via concentrations or precursor emissions) and land use change (in five models). The new aggressive mitigation scenario (E1), constructed using an integrated assessment model (IMAGE?2.4) with reduced fossil fuel use for energy production aimed at stabilizing global warming below 2?K, is studied alongside the medium-high non-mitigation scenario SRES A1B. Resulting twenty-first century global mean warming and precipitation changes for A1B are broadly consistent with previous studies. In E1 twenty-first century global warming remains below 2?K in most models, but global mean precipitation changes are higher than in A1B up to 2065 and consistently higher per degree of warming. The spread in global temperature and precipitation responses is partly attributable to inter-model variations in aerosol loading and representations of aerosol-related radiative forcing effects. Our study illustrates that the benefits of mitigation will not be realised in temperature terms until several decades after emissions reductions begin, and may vary considerably between regions. A subset of the models containing integrated carbon cycles agree that land and ocean sinks remove roughly half of present day anthropogenic carbon emissions from the atmosphere, and that anthropogenic carbon emissions must decrease by at least 50% by 2050 relative to 1990, with further large reductions needed beyond that to achieve the E1 concentrations pathway. Negative allowable anthropogenic carbon emissions at and beyond 2100 cannot be ruled out for the E1 scenario. There is self-consistency between the multi-model ensemble of allowable anthropogenic carbon emissions and the E1 scenario emissions from IMAGE?2.4. |
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