Klaus Keller, now at Penn State, has been analyzing two interrelated questions. First, how can we understand, detect, and predict potential anthropogenic threshold responses of the climate system? Second, how can we use this scientific information to design sound risk-management strategies?


Predicting changes in ocean circulation

One potential climate threshold response involves an abrupt and/or persistent weakening of the North Atlantic meridional overturning circulation (AMOC), an ocean circulation system that transports heat from low latitudes to the North Atlantic basin and the surrounding regions. The geologic record and model simulations suggest that the AMOC may weaken or even collapse in response to climatic forcing. Such a threshold response could be associated with considerable ecological and economic impacts. The current predictions about the future fate of the AMOC are, however, deeply uncertain.

Over the past year, Keller and colleagues analyzed the effects of potential climate threshold responses (such as an abrupt and/or persistent shutdown of the North Atlantic Meridional Overturning Circulation, AMOC) on economically efficient climate strategies. One particular focus was on the potential value of AMOC observation systems to improve the design of climate strategies. They showed, for example, that the currently implemented and well-tested AMOC observation system may well fail at the task of providing a confident prediction of an approaching AMOC shutdown before the forcing threshold has been crossed. However, investments in an AMOC observation system that would enable a confident and early prediction of an AMOC shutdown would likely pass an economic cost-benefit test. In ongoing work, they are also analyzing the risks of recently proposed geoengineering proposals.