On the (Nonlinear) Causes of Abrupt Climate Change During the Last Ice Age

Jose A. Rial [jar@email.unc.edu], University of North Carolina, Chapel Hill

Simulation of paleoclimate proxy time series with simplified mathematical models is a potentially rich source of insight into the evolution of the earth’s climate. I have recently tried a model for the Dansgaard-Oeschger oscillations in which the north Atlantic climate system is mathematically described as a nonlinear thermal oscillator (e.g., Saltzman et al.,1981; J. Atmos. Sci., 38, 494-503) externally forced by the insolation. The model suggests that the GRIP record is strongly influenced by the astronomical forcing, and close inspection suggests that frequency modulation of the sea-ice/ocean/atmosphere thermal oscillator by the astronomical input is the main cause of most of the peculiar distribution of warming events in the GRIP record. Notably, the model reproduces the Younger Dryas episode quite well, so that it may provide useful predictions of global warming at the millennial scale. The challenge is to construct a complete model that incorporates as much of the physics as possible, using all the relevant climate variables (including geography), and hopefully demonstrate that it is indeed equivalent to a forced, self-sustained, nonlinear relaxation oscillator.