Post on 01-Apr-2015
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: didier.swingedouw@cea.fr
Thank you