Didier Swingedouw

1
Projections of the thermohaline circulation in
OAGCMs toward an understanding of
uncertainties

• Didier Swingedouw
• Laboratoire des Sciences du Climat et de
  lEnvironnement
• France

2
Thermohaline circulation

• THC a system with complex feedbacks
• Coupled with the atmosphere an AOGCM is
  necessary

3
Greenland melting impact on the THC
Scenario of CO2 doubling, stabilised during 430
ans
4
Impact of the THC on global warming after 500
years
NIS2 - CTRL
WIS2 - CTRL
Années de simulation
5
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_at_cea.fr