"...Two million years ago forests extended nearly to the north pole.
And as recently as 125,000 years ago, temperatures were so high that hippopotami and other animals now found only in Africa made their homes in northern Europe.
Fig. 2.2
Temperature curve for the last 6 million years, based on an ocean core. (Carter, 2006)
The past million years have seen 8 to 10 ice ages, each about 100,000 years long, with short, warm interglacial periods of about 10,000 years.
The difference in globally averaged temperatures between glacials and interglacials is about 5°C.
The transition between glacial and interglacial conditions can take place in less than a thousand years - sometimes in as little as decades. Such dramatic climatic shifts occurred near the end of the last major ice age, about 15,000 years ago.
First, a brief warming occurred, and then the ice age returned for roughly a thousand years. Finally, by 11,500 years ago, the climate quickly warmed again. Ice core data indicate that temperatures in central Greenland rose by 7°C or more in a few decades.
(Marshall Institute, 2006, p. 27)..."
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