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Chapter 8- Climate Changes

Chapter 8- Climate Changes - Climate change can be defined...

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Climate change can be defined as a change in any statistical property of the atmosphere, such as a change in mean temperature. However, changes in climate may occur even though the mean values of precipitation, temperature, and wind remain the same over time.
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The geologic column.
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For most of its life, Earth has been largely free of permanent (year-round) ice. It is a warm planet, punctuated by perhaps seven relatively brief ice ages. The warm times persist for hundreds of millions of years to billions of years, whereas the ice ages last on the order of tens of millions of years to perhaps a hundred million years. Oscillations in temperature and ice cover are called glacial/interglacial cycles.
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In the depths of the last glaciation, around 20,000 years ago, land ice covered much more area as seen in the map above. Sea level was about 120 m lower than it is now, so that a land bridge existed between Siberia and Alaska.
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Warming began about 15,000 years ago, interrupted about 2,000 years later by the Younger Dryas , a time when colder conditions returned for about 1,200 years. 11,800 years ago another period of abrupt warming began bringing climate into the present interglacial.
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There is evidence that the period a.d. 900–1200 was warm in the North Atlantic. This Medieval Warm Period , coincides with the Viking settlement of Greenland. The so-called Little Ice Age , from 1450 to 1850, was a cold period for western Europe as alpine glaciers advanced and temperatures fell by about 0.5 to 1°C.
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Persistent oscillations emerge for every time period going back 500,000 years. These millennial-scale oscillations appear at intervals of 6000, 2600, 1800, and 1450 years.
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