Is possible to constrain models climate sensitivity using paleo proxy-data ? Hugues Goosse, Marie-France Loutre, Thierry Fichefet, Université catholique de Louvain, Belgium Jesus Fidel Gonzalez-Rouco, Universidad Complutense de Madrid, Spain Hugo Beltrami, Environmental Sciences Research Centre, Nova Scotia, Canada

Description of LOVECLIM LOVECLIM (3D) ECBilt (atmosphere) AGISM (ice sheets) CLIO (sea ice-ocean) VECODE (terr. biosphere) LOCH (oceanic carbon cycle) ECBilt (Opsteegh et al., 1998) Quasi-geostrophic atmospheric model (prescribed cloudiness; T21, L3). CLIO (Goosse and Fichefet, 1999) Ocean general circulation model coupled to a thermodynamic- dynamic sea ice model (3 x 3, L20). VECODE (Brovkin et al., 2002) Reduced-form model of the vegetation dynamics and of the terrestrial carbon cycle (same resolution as ECBilt). LOCH (Mouchet and François, 1996) Comprehensive oceanic carbon cycle model (same resolution as CLIO). AGISM (Huybrechts, 2002) Thermomechanical model of the ice sheet flow + visco-elastic bedrock model + model of the mass balance at the ice-atmosphere and ice-ocean interfaces (10 km x 10 km, L31).

Testing different model configurations Description of the experiments. Model parameters are selected to provide different model behaviour, e.g. climate sensitivity, response of the maximum of the MOC to a 0.2 Sv freshwater flux in the North Atlantic, … Climate sensitivity (K) Decrease of the maximum of the MOC (%) X E1 X E2 X E3 X E5 X E4 X X X X X X

Annual mean temperature anomaly averaged over the northern Hemisphere during the last 1000 years E2 E3 E4 E5 E1 Time Temperature anomaly Testing different model configurations

Annual mean temperature anomaly averaged over the northern Hemisphere during the last 8000 years E2 E3 E4 E5 E1 Time Temperature anomaly Testing different model configurations

Model-data comparison of underground temperatures Borehole reconstructions Concept Geothermal gradient Summer Winter

Model-data comparison of underground temperatures Borehole reconstructions Concept

Model-data comparison of underground temperatures Gonzalez-Rouco et al Forward model 894 grid points Inversion + Lat weighted avg. Replicating the borehole method using ECHO-G GCM as surrogate reality Model SAT Reconstruction

Model-data comparison of underground temperatures Stevens et al Forward-modeled profiles produced from a simulation performed using ECHO-G compared to observations (in black). The various grey, red and green cruves are computed from model results suing various reference level. We need an adequate reference to compute anomalies !

E2 E3 E4 E5 E1 Changes in sea-ice extent in the Arctic Location of the September ice edge in the 5 experiments Pre-industrial conditions averages Goosse et al. 2007

E2 E3 E4 E5 E1 Changes in sea-ice extent in the Arctic Location of the September ice edge in the 5 experiments Early Holocene conditions (8kyr Bp) averages (Scenario Sres B1) Goosse et al. 2007

Link between the minimum Arctic sea ice extent (in 10 6 km 2 ) for the early Holocene and the period AD (scenario SRES B1) Changes in sea-ice extent in the Arctic

Time evolution of the minimum ice extent in the Arctic over the period AD Scenario SRES B1 Scenario SRES A2 Goosse et al. 2007

Conclusions  Paleo-proxy data could efficiently be used to constrain model behavior.  They could provide complementary information compared to the one obtained from the recent past.  Accurate data are required, with a good spatial sampling and one should take care of the methodology used for model-data comparison.