[LaMudBug]

There’ve been 20 periods of glacial advance ~ we are about 5,000 years overdue for the 21st period.

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Would you be kind enough to share the data source of “20 periods” and “5,000” years. Thanks....

[pwatson]

This shows a good visual, http://www.windows.ucar.edu/tour/link=/earth/climate/cli_sun.html

Its the Sun spot cycle, plus the Milankovitch Cycles that cause temperature changes on the planet.