Part I. Variability of the Tropical Pacific Coupled Ocean-Atmosphere System: Precessional Response, Abrupt Change and Sub-Milankovich Frequencies. Part II. Global Connections

A. C. Clement (Lamont-Doherty Earth Observatory, Palisades, NY 10964; ph. 914-365-8691; fax 914-365-8736; Internet: clement@rosie.ldeo.columbia.edu); M. A. Cane (Lamont-Doherty Earth Observatory, Palisades, NY 10964; ph. 914-365-8344; fax 914-365-8736; Internet: mcane@ldeo.columbia.edu)

This presentation will consist of two parts. The first will focus on low frequency variability in the tropical climate alone. The second will discuss the potential role of the tropics in global climate change.

(I) A model of the tropical Pacific coupled ocean-atmopshere system is run for 700,000 years with Milankovich forcing, and for 150,000 with no forcing. The model shows a response to the precessional cycle in solar forcing (a period of about 20,000 years) with abrupt transitions between warm and cold states in the eastern equatorial Pacific, and the relevant mechanism is discussed. A climate record from the eastern equatorial Pacific is introduced as evidence that such a mechanism may have been operating in the Quarternary. Both the forced and unforced model runs show power at sub-Milankovich frequencies, and model physics operating at these frequencies will be discussed.

(II) We offer the hypothesis that millenial changes, abrupt changes, and glacial cycles are all generated by nonlinear interactions of the ocean and atmosphere in the tropical Pacific. We will spend some time explaining why changes in the conveyor are highly unlikely to cause global climate change, whereas the tropical Pacific changes should generate changes in the conveyor. In addition, we will try to show that the tropical Pacific mechanism for tropical Pacific climate change discussed in part I can account for features of the global climate record.