Abstract

The possibility of a reduced Atlantic thermohaline circulation in response to increases in greenhouse-gas concentrations has been demonstrated in a number of simulations with general circulation models of the coupled ocean–atmosphere system. But it remains difficult to assess the likelihood of future changes in the thermohaline circulation, mainly owing to poorly constrained model parameterizations and uncertainties in the response of the climate system to greenhouse warming. Analyses of past abrupt climate changes help to solve these problems. Data and models both suggest that abrupt climate change during the last glaciation originated through changes in the Atlantic thermohaline circulation in response to small changes in the hydrological cycle. Atmospheric and oceanic responses to these changes were then transmitted globally through a number of feedbacks. The palaeoclimate data and the model results also indicate that the stability of the thermohaline circulation depends on the mean climate state.

1. Department of Geosciences, Oregon State University, Corvallis, Oregon 97331, USA
2. College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA
3. Climate and Environmental Physics, University of Bern, Physics Institute, Sidlerstrasse 5, 3012 Bern, Switzerland
4. School of Earth and Ocean Sciences, University of Victoria, PO Box 3055, Victoria, British Columbia V8W 3P6, Canada

Correspondence to: Peter U. Clark¹ Correspondence and requests for materials should be addressed to P.U.C. (e-mail: Email: clarkp@ucs.orst.edu).