2006: Towards a risk assessment for shutdown of the Atlantic thermohaline circulation. Avoiding Dangerous Climate Change

• Main Authors: Richard Wood, Matthew Collins, Jonathan Gregory, Glen Harris, Michael Vellinga
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: North Atlantic
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.319.5533; http://stabilisation.metoffice.com/33_Richard_Wood.pdf

The possible shutdown of the Atlantic Ocean Thermohaline Circulation (THC) has attracted considerable attention as a possible form of dangerous climate change. We review evidence for and against three common assertions, which imply that THC shutdown could pose particular problems for adaptation: first, associated climate changes would be in the opposite direction to those expected from global warming; secondly, such changes could be rapid (timescale one or two decades); and thirdly the change could be irreversible. THC shutdown is generally considered a high impact, low probability event. Assessing the likelihood of such an event is hampered by a high level of modelling uncertainty. One way to tackle this is to develop an ensemble of model projections which cover the range of possible outcomes. We present early results from a coupled GCM ensemble, demonstrating the feasibility of this approach, and discuss prospects for a more objective THC risk assessment in future. 1. Review of current knowledge 1.1 Impact of the THC on climate The THC, or more precisely the meridional overturning circulation (MOC), transports around 10 15 W of heat northwards in the North Atlantic [1]. This heat is lost to the atmosphere northwards of about 24°N, and