Project # : S02-13-01
1. PROJECT TITLE : The effect of Arctic Ocean processes on global climate change
2. PRINCIPAL INVESTIGATOR(S) : A. J. Weaver
3. COLLABORATOR(S ) :O. A. Saenko and M. Eby
4. PROGRESS (for 1 July through 30 September 2003) :
(i) Several 140 year experiments looking at the response of the thermohaline circulation (THC) to separate thermal and fresh water fluxes due to global warming have been completed. The daily fresh water fluxes from a preindustrial (control) and a global warming experiment were saved. Both of the experiments were rerun but with their fresh water forcing switched. Analysis of the THC response allows us to separate the response to each forcing. Many other modeling groups are interested in carrying out similar experiments and initial results were discussed in a recent meeting in Hamburg. Even the sign of the THC response to fresh water forcing is uncertain at the moment. Unlike other groups, we have carried out experiments where the fresh water flux is switched both above and below sea ice. This allows us to separate out the sea ice fresh water flux response. It appears that the fresh water fluxes from sea ice play a critical role in the response of the THC in our model. Specifically, the retreat of sea ice greatly decreases the reduction in the THC under global warming. The different treatment of sea ice, in various models, may thus provide a clue to the different model responses. Analysis of preliminary results is continuing. These experiments will also be run out to equilibrium and the results will form part of the paper in preparation (see below).
ii) The paper which discusses the role of sea-ice extent on the thermohaline circulation is in the process of being reviewed (see below).
As shown in previous experiments funded under this project, ice extent in the North Atlantic appears to play a critical role in determining the transient response of the THC. Climate models show considerable variation in their THC response to global warming. Understanding these differences is necessary to reduce the uncertainty in the models predictions. Our experiments show that Arctic processes, especially those involving sea ice, may be important in understanding and predicting the THC and thus the climate response to global warming.
Papers in preparation, in press, or completed that will be acknowledging CCAF funding are as follows:
Eby M., O. A. Saenko and A. J. Weaver, 2003: Response of the thermohaline
Circulation, in a coupled model, to global warming, fresh water forcing,
Saenko O. A., M. Eby and A. J. Weaver, 2003: The effect of sea-ice extent in the
North Atlantic on stability of the thermohaline circulation in global warming
experiments, Climate Dynamics, submitted.
Saenko O. A., E. C. Wiebe and A. J. Weaver, 2003: North Atlantic response to
the above-normal export of sea ice from the Arctic. J. Geophys. Res.,
Vol. 108, No C7, 3224, doi:10.1029/2001JC001166.
5. ANY COMMENTS OR CONCERNS ON STATE OF PROGRESS : None
6. PREPARED BY: A. J. Weaver
7. DATE: October 15,2003
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