The formation rate of North Atlantic Deep Water (NADW) and the intermediate-depth Labrador Sea Water (LSW) tightly governs the strength of the Atlantic meridional overturning circulation (AMOC) and thus the circulation of heat in the world’s oceans. Through complex ocean atmosphere circulation models, much past research has sought to observe whether global warming from increasing manmade greenhouse gas emissions will melt ice caps and introduce freshwater to the North Atlantic, thereby slowing NADW and LSW formation. Weaver et al. ran several models with varying initial conditions and found that the strength of the AMOC always declines when greenhouse gases are increased by one percent per year, with largest declines in those experiments with the strongest initial AMOC. Further, they confirm that changes in surface heat flux, rather than changes in surface freshwater flux (i.e., increased precipitation, evaporation, and river runoff), slow down the AMOC, an idea suggested by past research. Finally, the authors note that their models were strongly influenced by water vapor and snow/ice feedbacks, and were thus sensitive to mean climate conditions.

Title: The response of the Atlantic meridional overturning circulation to increasing atmospheric CO2: Sensitivity to mean climate state

Authors: Andrew J. Weaver and Michael Eby: School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada; Markus Kienast: Department of Oceanography, Dalhousie University, Halifax, Nova Scotia, Canada; Oleg A. Saenko: Canadian Centre for Climate Modelling and Analysis, University of Victoria, British Columbia, Canada.

Source: Geophysical Research Letters (GRL) paper 10.1029/2006GL028756, 2007