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The Complex Physics of Climate Change: Nonlinearity and Stochasticity

Lecture by Michael Ghil

Held on Wednesday 14th March 2012

Michael Ghil

Ecole Normale Supérieure, Paris, and University of California, Los Angeles
Recent estimates of climate evolution over the coming century still differ by several degrees.

This uncertainty motivates in part the work presented in this talk.
The complex physics of climate change arises from the large number of components of the climate system, as well as from the wealth of processes occurring in each of the components and across them. This complexity has given rise to countless attempts to model each component and process, as well as to two overarching approaches to apprehend the complexity as a whole: deterministically nonlinear and stochastically linear. Call them the Ed Lorenz and the Klaus Hasselmann approach, respectively, for short.

We propose a “grand unification” of these two approaches that relies on the theory of random dynamical systems. In particular, we apply this theory to the problem of climate sensitivity, and study the random attractors of nonlinear, stochastically perturbed systems, as well as the time-dependent invariant measures supported by these attractors.

Results are presented for several simple climate models, from the classical Lorenz convection model to El Nino-Southern Oscillation models. Their attractors support random Sinai-Ruelle-Bowen measures with nice physical properties. Applications to climate sensitivity and predictability are discussed.

This talk is the result of recent collaborations with M. D. Chekroun, D. Kondrashov, J. C. McWilliams, J. D. Neelin, E. Simonnet, S. Wang, and I. Zaliapin.

Biography:

Professor Michael Ghil is Distinguished Professor of Atmospheric Sciences and Geophysics at the University of California, Los Angeles (UCLA), since July 1994, and Distinguished Professor of Geosciences (since September 2002) and Director of the Environmental Research and Teaching Institute (CERES-ERTI), since January 2003, at the Ecole Normale Supérieure (ENS), in Paris, where he also acted as Head of the Geosciences Department (July 2003-December 2009). He graduated with an MSc in Mechanical Engineering from the Technion–Israel Institute of Technology (Israel, 1971), before completing a PhD in Mathematics at the Courant Institute of Mathematical Sciences at New York University (USA). He has over 260 refereed journal articles and book chapters in areas ranging from the geosciences --- through applied mathematics, fluid dynamics, and nonlinear physics --- and on to macroeconomics; he has authored or edited a dozen books in these areas. Prof. Ghil is an Honorary Member of the Hungarian Academy of Sciences (2010), E. N. Lorenz Lecturer of the  American Geophysical Union (2005), Foreign Member of the Austrian Academy of Sciences (2005), G. Lemaître Chair, Université Catholique de Louvain, Belgium  (2004), Honorary Member of the Romanian Academy of Engineering Sciences (2004), Associate of the Royal Astronomical Society (2004), Member of the Academia Europaea (1998), Visiting Chair at the Collège de France (1997), Elf-Aquitaine/CNRS Chair and Medal of the Académie des Sciences (Paris, 1996), Fellow of the American Geophysical Union (1995), and Guggenheim Fellow (1991-92). He was also awarded two NSF Special Creativity Awards (1993-1995 and 1998-2000), as well as the L. F. Richardson Medal of the European Geosciences Union (2004). Professor Ghil was also recently awarded the European Geosciences Union’s top medal – the Alfred Wegener Medal – which he will receive in the forthcoming April 2012 EGU session. Prof Ghil’s of his 2012 Wegener Medal Lecture is entitled The Complex Physics of Climate Change: Nonlinearity and Stochasticity.