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A comparison of PMIP2 model simulations and the MARGO proxy reconstruction for tropical sea surface temperatures at last glacial maximum |
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| Authors: | Bette L Otto-Bliesner Ralph Schneider E C Brady M Kucera A Abe-Ouchi E Bard P Braconnot M Crucifix C D Hewitt M Kageyama O Marti A Paul A Rosell-Melé C Waelbroeck S L Weber M Weinelt Y Yu |
| Institution: | 1. Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO, USA 2. Institut für Geowissenschaften, Christian-Albrechts Universit?t, Kiel, Germany 3. Institut für Geowissenschaften, Eberhard-Karls Universit?t Tübingen, Tübingen, Germany 4. Center for Climate System Research, The University of Tokyo, Kashiwa, Japan 5. CEREGE, College de France, CNRS, Universite Aix-Marseille, Europ?le de l’Arbois, Aix-en-Provence, France 7. Laboratoire des Sciences du Climat et de l’Environnement, Unité mixte CEA-CNRS-UVSQ, Gif-sur-Yvette Cedex, France 8. Institut d’Astronomie et de Géophysique Georges Lema?tre, Université Catholique de Louvain, Louvain-la-Neuve, Belgium 9. Met Office Hadley Centre, Exeter, UK 10. Department of Geosciences, Bremen University, Bremen, Germany 11. ICREA and Institut de Ciencia i Tecnologia Ambientals, Universitat Autònoma de Barcelona, Barcelona, Spain 12. Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands 13. LASG, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, People’s Republic of China |
| Abstract: | Results from multiple model simulations are used to understand the tropical sea surface temperature (SST) response to the reduced greenhouse gas concentrations and large continental ice sheets of the last glacial maximum (LGM). We present LGM simulations from the Paleoclimate Modelling Intercomparison Project, Phase 2 (PMIP2) and compare these simulations to proxy data collated and harmonized within the Multiproxy Approach for the Reconstruction of the Glacial Ocean Surface Project (MARGO). Five atmosphere–ocean coupled climate models (AOGCMs) and one coupled model of intermediate complexity have PMIP2 ocean results available for LGM. The models give a range of tropical (defined for this paper as 15°S–15°N) SST cooling of 1.0–2.4°C, comparable to the MARGO estimate of annual cooling of 1.7 ± 1°C. The models simulate greater SST cooling in the tropical Atlantic than tropical Pacific, but interbasin and intrabasin variations of cooling are much smaller than those found in the MARGO reconstruction. The simulated tropical coolings are relatively insensitive to season, a feature also present in the MARGO transferred-based estimates calculated from planktonic foraminiferal assemblages for the Indian and Pacific Oceans. These assemblages indicate seasonality in cooling in the Atlantic basin, with greater cooling in northern summer than northern winter, not captured by the model simulations. Biases in the simulations of the tropical upwelling and thermocline found in the preindustrial control simulations remain for the LGM simulations and are partly responsible for the more homogeneous spatial and temporal LGM tropical cooling simulated by the models. The PMIP2 LGM simulations give estimates for the climate sensitivity parameter of 0.67°–0.83°C per Wm−2, which translates to equilibrium climate sensitivity for doubling of atmospheric CO2 of 2.6–3.1°C. |
| Keywords: | Last glacial maximum MARGO PMIP Tropical oceans Climate sensitivity |
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