From Ice Ages & Astronomical Causes
Brief Introduction to the History of Climate
by Richard A. Muller
In Figure 1-6, the 10 kyr years of agriculture and civilization appear as a sudden rise in temperature barely visible squeezed against the left hand axis of the plot. The temperature of 1950 is indicated by the horizontal line. As is evident from the data, civilization was created in an unusual time.
There are several important features to notice in these data, all of which will be discussed further in the remainder of the book. For the last million years or so (the left most third of the plot) the oscillations have had a cycle of about 100 kyr (thousand years). That is, the enduring period of ice is broken, roughly every 100 kyr, by a brief interglacial. During this time, the terminations of the ice ages appear to be particularly abrupt, as you can see from the sudden jumps that took place near 0, 120, 320, 450, and 650 thousand years ago. This has led scientists to characterize the data as shaped like a "sawtooth," although the pattern is not perfectly regular.
Figure 1-6 Climate of the last 3 million years
As can be clearly noted, we have been on a much longer trend downward trend overall across the last 3 million years with the 100kyr cycle deepening and becoming more pronounce on the downside. Entertaining the strong concept that continuation in the established 100kyr periodicity is hardly at an end with deep glacial eras yet to come.