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Didier Swingedouw Laboratoire des Sciences du Climat et de l’Environnement France

Projections of the thermohaline circulation in OAGCMs : toward an understanding of uncertainties. Didier Swingedouw Laboratoire des Sciences du Climat et de l’Environnement France. Uncertainty for the future. Thermohaline circulation. THC : a system with complex feedbacks

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Didier Swingedouw Laboratoire des Sciences du Climat et de l’Environnement France

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

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

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

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

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

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

  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 Uncertainty • 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. • 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 High resolution simulation of last decades (MERCATOR, DRAKKAR) • OVIDE and RAPID section • Paleoclimate record of 8.2 event Observations 2 years

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

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