1. Didier Swingedouw Laboratoire des Sciences du Climat et de l’Environnement France Projections of the thermohaline circulation in OAGCMs: toward an understanding of uncertainties

2. Thermohaline circulation  THC : a system with complex feedbacks  Coupled with the atmosphere : an AOGCM is necessary Uncertainty for the future

3. Greenland melting impact on the THC WIS2 CTRL NIS2 Scenario of CO2 doubling, stabilised during 430 ans Temps (années) CO2 ( ppm ) 0 70 500 280 560 CTL Scénario Temps (année s) CTRL WIS2 NIS2 Mean global Temperature Snow Land Ocean Glacier Two different IPSL-CM4 models: one with land-ice melting, the other without

4. Impact of the THC on global warming after 500 years NIS2 - CTRLWIS2 - CTRL Années de simulation WIS2 CTRL NIS2

5. Feedback quantification + - t=0 Sans-CTL Avec-CTL with Density budget at the convection sites :

6. Main THC feedbacks Dynamical gain of the THC system Climate system Density flux of Température Density flux of salinity THCeTHCs + -

7. CNRS project : understanding THC uncertainties in IPCC projections  Apply feedback model to « water hosing » CMIP : quantification of differences in feedback processes among IPCC models  Comparison of models with ocean « observations » in transient phase :  Last decades  Paleoclimate 8.2 event  Role played by atmospheric forcing and ocean resolution in scenarios

8. Models High resolution simulation of last decades (MERCATOR, DRAKKAR) Analysis of« water-hosing » = evaluate differences in ocean processes among IPCC models Coupling ice-sheet model GREMLINS with IPSL-CM4 Simulation of paleoclimatic event 8.2. Observations OVIDE and RAPID section Paleoclimate record of 8.2 event Representation of existing processes (feedbacks …) Missing process : Greenland melting Paléoclimatical constrain on IPSL-CM4 Dynamical constrain of last 50 years High resolution constrain on key sections Uncertainty 2 years

9. Models Observations Uncertainty Atmospheric forcing uncertainty Ocean resolution impact Paleoclimate constrain for all IPCC models Climatic impact of THC NEMO with 4 different atmospheric model different oceanic resolution Analysis of PMIP2 database of 8.2 event OVIDE and RAPID section Paleoclimate record of 8.2 event High resolution simulation of last decades (MERCATOR, DRAKKAR) 4 years

10. Conclusions Better evaluation of:  IPCC models against different observation datasets  Ice-sheet melting interaction with THC in IPSL-CM4  Ocean resolution issues in coupled models with NEMO  Uncertainty related to atmospherical forcing of NEMO

11. mailto: didier.swingedouw@cea.fr Thank you