Abstract: It is a highly controversial issue that there will be an abrupt and large climate change induced by the reorganization of the Atlantic thermohaline circulation in a warming climate. In order to understand this issue, the past abrupt climate change events and some hypotheses on the causes are first reviewed. Some recent research results from the McGill Earth System Modelling group on the past abrupt climate changes are then presented. Also, Southern-Northern Hemispheric teleconnections related to the reorganization of the Atlantic thermohaline circulation are summarized. Lastly, a discussion on our ability to predict such a future abrupt climate change is also given. The studies on the past abrupt thermohaline circulation changes show that the background climates that are responsible for past abrupt thermohaline circulation changes are different from the modern climate and the future warm climate. Therefore, it is not possible to conclude that there will be such a future abrupt climate change, based on paleoclimate studies. Although some climate models predict that the Atlantic thermohaline circulation will be weakened or even shut down by increased atmospheric CO2 levels, we are still not sure that such an abrupt climate change will happen because more observational data are needed for us to validate model results and there are significant uncertainties in climate models.

Key words: Atlantic thermohaline circulation, abrupt climate changes, Southern-Northern Hemispheric teleconnections, McGill Earth System Modelling