Group seminar on 4. April, 15:15 CET, Bundessstr. 53, Room 022/023
Multiple equilibria and rapid transitions in complex Earth System models - Tipping in ESMs
Prof. Dr. Martin Claußen
In his pioneering paper on stochastic climate models (Tellus, 1976), Klaus Hasselmann wrote: “A basic difficulty of unstable feedback models (apart from - or possibly because of – their high degree of idealization) is that they tend to predict climatic variations as flip-flop transitions and therefore fail to reproduce the observed continuous spectrum of climatic variability.” This statement refers to highly idealized energy budget models for which “climate catastrophes”, i.e. abrupt changes between climatic states triggered by small perturbation in external forcing, were found. With the advance of complex models of the Earth’s climate system – fostered by Klaus Hasselmann and Günter Fischer of the Meteorological Institute in the early 1980s – it was time to explore the possibility that flip-flop transitions were not just an artifact of overly simple climate models. This chapter discusses three examples of multiple equilibria and rapid transitions in the climate system: the Snowball Earth, the Atlantic Meridional Overturning Circulation, and the climate-vegetation interaction. The examples start with predictions from idealized models, followed by detection of abrupt transitions found in paleo climate proxies which fostered simulation of unstable feedbacks using complex models. In all examples, significant contributions emerged from climate research in Hamburg.