CCAF-Science Quarterly Report for Period Ending 30 June 2003

Project # : S02-13-01

1. PROJECT TITLE : The effect of Arctic Ocean processes on global climate change


3. COLLABORATOR(S ) : O. A. Saenko and M. Eby

4. PROGRESS (for 1 April through 30 June 2003) :

  1. Progress achieved
  2. (i) In accordance with the primary objective of this project, which is to investigate the effects of Arctic Ocean related processes on global climate, we conducted numerical experiments to investigate the role of sea-ice extent in the North Atlantic on the transient response of the ocean thermohaline circulation (THC) to the increasing atmospheric CO2 concentrations. The results of these experiments have been summarized into a paper, which we have just submitted to the Climate Dynamics (see below).

    (ii) In parallel, we continue performing experiments directed towards understanding the relative importance of heat and freshwater fluxes for the stability of THC in the warming climate, using our global climate model.

    The results of these experiments will be described in our next progress report.

    (iii) Finally, we have investigated to role of the above-normal export of sea-ice from the Arctic to the northern North Atlantic on the stability of the THC. The results of these experiments have appeared in the recent issue of the Journal of Geophysical Research (see below).

  3. Milestones attained
  4. As reported in the last IPCC report (IPCC, 2001), different climate models show considerably different response of the ocean THC to the radiative forcing, associated with the projected for 21st century increase of greenhouse gases in the atmosphere. The reason for that diversity in the simulated THC responses was not clear. We have shown that this can be in part explained

    by strong sensitivity of the THC response to the sea-ice extent in the North Atlantic. Specifically, we showed that a climate model which overestimates sea-ice extent is likely to have more stable THC. The key reason for such a result is a retreat of sea-ice, which reduces direct input of freshwater into the regions of deep water formation. The contributes to the overall reduction of surface freshwater flux in the subpolar North Atlantic, thereby stabilizing the THC.

  5. Deliverables completed

Papers in preparation, in press, or completed that will be acknowledging CCAF funding are as follows:

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.


6. PREPARED BY: A. J. Weaver

7. DATE: July 23, 2003

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