event
Wednesday 26 Sep 2012: Vagaries of an astronomical synchronisation: shall we jump to another paleoclimate history?
Bernard De Saedeleer - UCL, Belgium
Harrison 203 11:00-12:00
The mystery of 100 kyr ice ages on Earth has drawn ceaseless attention for several decades. A very widespread school of thought assumes that these paleoclimates are paced by a varying incoming solar radiation (the so-called “Milankovitch forcing” by insolation). This phenomenon is clearly related to the synchronisation phenomenon in nonlinear sciences. A persistent hypothesis in the literature is the uniqueness of the associated paleoclimate history. In this talk, we challenge that hypothesis by investigating in depth the synchronisation properties of a simple paleoclimatic toy model (a van der Pol-like relaxation oscillator). Our approach mainly relies on tools borrowed from dynamical system theory and clustering analysis. We show that, in a deterministic framework, the astronomical forcing may synchronise the ice volume to several coexisting climatic attracting trajectories, and that temporary desynchronisations may occur due to loss of local stability (positive largest local Lyapunov exponent). Additional disturbances may then cause a jump to another climate history over the last millions years of the Pleistocene, reducing the predictability of the timing of the glacial inceptions and terminations. Extensive Monte Carlo experiments confirm these results and precise them further. Such a conclusion about predictability is of major importance, because of its potential impact on the overall theory of ice ages.