Does the recent freshening trend in the North Atlantic indicate a weakening thermohaline circulation?

Abstract

It is widely expected that the thermohaline circulation of the ocean will slow down as greenhouse gas concentration in the atmosphere increases. This is partly due to an intensified hydrological cycle in a warmer climate. Is the recent observed freshening trend in the North Atlantic an indication of what has been expected? We report a similar freshening trend reproduced in an ensemble of four coupled model simulations with all major historical external (natural and anthropogenic) forcings. The modelled freshening trend originates from the Arctic Ocean where sea ice decrease and river runoffs increase with the same trend. Instead of weakening, we find an upward trend in the North Atlantic meridional overturning circulation. Copyright 2004 by the American Geophysical Union.