MULTIPLE STABLE CLIMATE MANIFOLDS AND ABRUPT CLIMATE TRANSITIONS

Among the most intriguing enigmas of the climate system is that on the one hand, the earth’s climate appears to be exquisitely sensitive to relatively minor variations in the distribution of insolation owing to orbital variations, but on the other hand it is in a grosser sense stable in that its oceans have not frozen over (at least not in the last 500 million years) or boiled away. To this enigma may be added the evidence that climate may undergo extraordinarily abrupt transitions. An attractive idea to help explain these characteristics is the notion that the earth possesses a limited number of stable climate regimes that may overlap to produce multiple equilibrium states for the same solar forcing. Here we present a theory and simple model that produces such overlapping stable equilibria, based on a few key feedback processes. These include control of atmospheric clouds and water vapor by the large scale circulation of the atmosphere, control of the depth and intensity of the ocean’s thermohaline circulation by atmospheric storms, and the relationship between atmospheric CO2 content, ocean temperature, and the strength of the thermohaline circulation. We will show that these key feedback processes produce a climate with three stable, overlapping climate manifolds. Subjecting this system to variations in climate forcing can account for many observed features of the climate system, including abrupt transitions, sensitivity to orbital variations, arctic warmth and high bottom water temperature during the Eocene, tempestites, and episodes of deep ocean anoxia during the Cretaceous.