The past climate of the Earth.

The climate of a given area at a specific time in the past. Paleoclimates can be read from the rocks much as areas with different types of climates produce sediments with specific characteristics today.

data and models show that major changes in ocean circulation can be caused by freshwater additions to the oceans from the movement and melting of sea ice or ice sheets and can result in rapid and dramatic changes in climate. Abrupt shifts in climate have had adverse effects on human civilizations in the past. Paleo climate data suggest that the collapse of the Mesopotamian Empire about 4,200 years ago (2,200 BC) corresponds to a sharp cooling event (Alley & deMenocal, 1998)