Natural_Climate_Variability_F10_Lect10

Natural_Climate_Variability_F10_Lect10 - Natural Climate...

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Natural Climate Variability Fall 2010, Lecture 10 1
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Discovery of an Ice Age Louis Agassiz, a Swiss- American scientist and physician, was the first to recognize evidence for an ice age Trained in medicine and natural history, he was the first to propose, in 1837, that earth had been subjected to a past ice age 2 1807 - 1873
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Louis Agassiz Agassiz moved to the United States in 1846 He became professor of zoology and geology at Harvard University, and founded the Museum of Comparative Zoology He became interested in the last glacial advance in North America, and studied it for the remainder of his life 3
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4 Ice Ages Ice ages - are times when the entire Earth experiences notably colder climatic conditions During an ice age The polar regions are cold There are large differences in temperature from the equator to the pole Large, continental-size glaciers or ice sheets can cover enormous regions of the earth
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Previous Ice Ages The climate history of earth is under active investagation Two Precambrian ice ages are known 2000 MYBP 600 MYBP Late Paleozoic ice age, about 250 MYBP Pleistocene ice age 5
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Late Paleozoic Glaciation 6
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Plate Tectonics and Climate Glaciers can only form on land As plates move, evidence for a cold climate, in the form of glaciation, exists primarily when land masses are present at high latitudes Movement of land masses also alters the oceanic circulation pattern, a vital factor in determining climate conditions 7
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8 Pleistocene Glaciation Began about 1.6 MYBP There were at least 4 glacial advances Climate cooled 5-10ºC during glacial episodes, warming in between Last episode peaked 18,000 years ago, ice covering about 30% of the earth’s surface
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9 North American Ice Cover Figure shows the extent of ice cover from 18,000 to 8000 years ago White is ice, blue is glacial meltwater lakes
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Climate Questions What causes the onset of glacial conditions? What caused the alternation of glacial and interglacial conditions during the Pleistocene? 10
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Natural Variability The earth’s climate has a fairly large natural variability Before we examine how much man is changing climate, we need to understand what contributes to natural variability We also need to remember what causes earth’s seasons 11
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What Causes Earth’s Seasons 12
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Orbital Influence on Climate The earth’s orbit around the sun, modified by its interaction with other bodies in the solar system, and rotation around its own axis, influence climate 13
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