"Human beings have never experienced the earth's normal climate. For most of it's 4.6 billion year old existance , the planet has been inhospitably hot or dry and utterly devoid of glacial ice. Only seven times have major ice eras, avergaing roughly 50 MILLION years in length, introduced relatively cooler temperatures; humankind arose during the most recent of these periods."

"When the Pleistocene ice epoch began about 2.4 million years ago, advancing ice sheets marked the onset of obe of the coldest climatic interludes experienced on earth. These periods of especially vigorous glacial advances (COLD) are known as the ice ages."

"The most recent ice age began about 120,000 years ago... It reached it's bitter extreme (COLD) some 50,000 years later, slowly moderated, then brought severe cold again about 18,000 years ago. In the last 10,000 years (The Holocene Interglacial) three sustained cold spells sent temperatures below the geologically current global average (past 10,000 years)."

A gentle and gradual warming trend has occurred since then.

p.20. Planet Earth: Ice Ages (Time Life), published 1983.