Glacial Cycles: Extreme Natural Climate Change Events, and Still an Unsolved Puzzle...
Monday, September 24, 2001 - 3:00pm - 4:00pm
The major glaciations that have occurred over the earth every 100,000 years during the past 1 million years are the largest natural climate variability signal in recent geological history. During each glaciation, global sea level dropped by 120 meters and this large amount of water has then accumulated as 2-3 km high glaciers over land; global temperature varied by many degrees, and the concentration of CO2 in the atmosphere changed by 30%. Understanding these large amplitude natural climatic events seems essential for us to be able to predict future climate change with reasonable certainty. In spite of the large amplitude and obvious significance of these events we still do not have an accepted theory for them. Some extremely varied theories were proposed for the mechanism of glacial cycles. Some of these theories suggested that the glacial cycles are a result of random noise processes, due to a stochastic resonance, external forcing by variations in solar radiation due to earth orbital changes, due to effects of the elasticity of the earth crust, self-sustained internal variability of the climate system, nonlinear chaotic dynamics, relaxation oscillations due to nonlinear sea ice-land ice interaction, and more. The phenomenology of glacial cycles will be briefly introduced and some of the main theoretical ideas regarding the possible mechanism of these cycles will be presented.