GEOG 108 Lecture 20.docx

GEOG 108 Lecture 20.docx - GEOG 108 – Earth’s Climate...

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GEOG 108 – Oct 24, 2018 - Earth’s Climate History o During most of the earth’s history global temperatures were probably 8-15C warmer than today o In the last 500 million years of climatic history warmer conditions were broken by glacial periods o Occurred at 460, 330, 170, 50, and 2 million years before present o The period from 2,000,000-14,000 B.P. is known as the Pleistocene or Ice Age o During this period, large glacial ice sheets covered much of north America, Europe, and Asia for extended periods of time o During the coldest periods of the ice age, average global temperatures were probably 4- 5C colder than they are today o Warming of the earth and glacial retreat began about 14,000 years ago (12,000 BC) o We call this period the Holocene epoch
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o During the Holocene, the earth experiences a number of climatic fluctuations o From 6000-4000BC average global temperatures reached their maximum level during the Holocene and were 1C warmer than they are today o Climatologists call this period the climatic optimum o After this period global temperatures experienced a cooling o The next major period of warmer temperatures occurred during the period 900-1200AD ( Medieval warm period or little climatic optimum ) o 1550-1850AD global temperatures were at their coldest since the beginning of the Holocene o Scientists call this period the little ice age o Little ice age – the average annual temperature of the northern hemisphere was about 1.0C lower than today
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