Paleo Slide Set: The Ice Ages
Insolation and global ice volume fluctuations.

When the data are filtered for solar insolation and global ice volume over the past 400,000 years, 
we see that insolation and global ice volume fluctuated at the same major frequencies: the precession 
cycle of 23,000 years and 19,000 years, the obliquity cycle of 41,000 years, and the eccentricity cycle 
of 100,000 years (n.b.: the data do not extend far enough back to test the 400,000 yr. eccentricity cycle). 
The curves are thus much more similar than they first appear. So what makes them look so different? 
The biggest difference between the insolation and global ice volume curves is the surprising amplitude 
of the 100,000-yr. eccentricity cycle in the ice-volume records. The Milankovitch theory predicts that 
changes in eccentricity have a smaller effect on climate than variations in precession and obliquity. 
But climatic records from across the globe suggest that the great ice sheets have advanced and retreated 
to a 100,000-yr. beat. Why this is so is one of the many questions that remain to be answered about 
ice ages and the forces that drive them. 

Photo Credits:
Thomas G. Andrews
NOAA Paleoclimatology Program