Didier Swingedouw Laboratoire des Sciences du Climat et de l’Environnement France Projections of...
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Transcript of Didier Swingedouw Laboratoire des Sciences du Climat et de l’Environnement France Projections of...
Didier Swingedouw
Laboratoire des Sciences du Climat et de l’Environnement
France
Projections of the thermohaline
circulation in OAGCMs: toward
an understanding of
uncertainties
Thermohaline circulation
THC : a system with complex feedbacks
Coupled with the atmosphere : an AOGCM is necessary
Uncertainty for the future
Greenland melting impact on the THC
WIS2
CTRL
NIS2Scenario of CO2 doubling, stabilised during 430 ans
Temps
(années)
CO2
(ppm)
0 70 500
280
560
CTL
Scénario
Temps
(années)
CTRL
WIS2
NIS2Mean global Temperature
Snow
Land Ocean
Glacier
Two different IPSL-CM4 models: one with land-ice melting, the other without
Impact of the THC on global warming after 500 years
NIS2 - CTRLWIS2 - CTRL
Années de simulation
WIS2
CTRL
NIS2
Feedback quantification
E S0G
1
i
n
+-
THCTHC
t=0t=0Sans-CTL
Avec-CTL
THC
Glaciers1
1
i
i
ii
iwith
Density budget at the convection sites :
STTSTSResiduResiduSurfaceSurfaceTransportTransport
i
-0,4
-0,2
0
0,2
0,4
0,6
0,8
1
1 2
Main THC feedbacks
0.3)(1
1
TS
G
Dynamical gain of the THC system
S T
Climate system
Density flux ofTempérature
Density flux of salinity
THCe THCs
)( S
)( T
+-
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
ModelsModels
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.
ObservationsObservations
• 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
ModelsModels
ObservationsObservations
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
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
mailto: [email protected]
Thank you