Surface Δ14C in the Atlantic Ocean (colored dots) overlaid on the simulated Δ14C from a an ocean model. The observed values are notably lower in the tropics due to upwelling off Africa that is not resolved in the model.

Temperatures in the Southern Hemisphere tend to rise and fall during the ice ages along with insolation variations in the Northern Hemisphere. It is not at all obvious how this comes about.  In this lecture I will describe a new way for wobbles of the Earth's axis to influence the tropics and then both hemispheres at the same time. The mechanism is based on ocean temperatures that vary in response to monsoon winds and the heating of the northern continents during the summertime. The temperature variations come from upwelling variations along the coast of Africa.