Campuses:

Quaternary Glaciations and Celestial Mechanics

Tuesday, October 30, 2001 - 11:00am - 12:00pm
Keller 3-180
Michael Ghil (University of California, Los Angeles)
This talk attempts to bridge the two themes of the present workshop, climate dynamics and celestial mechanics. To do so, we focus on the relatively recent paleoclimate of the last 2 My, the Quaternary era. The evidence for climatic variability on this time scale is reviewed, based on proxy records from deep-sea sediments and ice cores. The climatic subsystems that are active over the Quaternary are discussed, along with the feedback mechanisms that couple them. These include the atmosphere, oceans, land and sea ice among the subsystems, as well as ice-albedo, precipitation-temperature and load-accumulation feedbacks between them.

The simplest mathematical models that capture the recorded variability are systems of nonlinear ordinary differential equations (ODEs). Multiple equilibria and limit cycles arise in these forced-dissipative ODE systems via saddle-node and Hopf bifurcations, respectively, for constant forcing. The quasi-periodic changes in insolation that are due to orbital variations lead to a number of interesting phenomena: nonlinear resonance, frequency locking, and transition to chaos. The music of the spheres is captured by the climate system through combination tones that were predicted by these models and confirmed by the analysis of higher-resolution proxy records.

References

Ghil, M., R. Benzi, and G. Parisi (Eds.), l985: Turbulence and Predictability in Geophysical Fluid Dynamics and Climate Dynamics, North-Holland Publ. Co., Amsterdam/New York/Oxford/ Tokyo, 449 pp.

Ghil, M., and S. Childress, 1987: Topics in Geophysical Fluid Dynamics: Atmospheric Dynamics, Dynamo Theory and Climate Dynamics, Springer-Verlag, New York/Berlin/London/Paris/ Tokyo, 485 pp.

Ghil, M., 1994: Cryothermodynamics: The chaotic dynamics of paleoclimate, Physica D, 77, 130-159.

Ghil, M., 2001 (PDF file): Hilbert problems for the geosciences in the 21st century, Nonlin. Proc. Geophys., 8, 211-222.

Ghil, M., 2001 (PDF file): Natural climate variability, in Encyclopedia of Global Environmental Change, Vol. 1 (M. MacCracken & J. Perry, eds.), Wiley & Sons, Chichester/New York, in press.

N.B. The latter two references can be found as PDF files at http://www.atmos.ucla.edu/tcd/ .