Ferg_Ch_12_Lecture

Ferg_Ch_12_Lecture - Climate change and severe weather Glacial Advance and Retreat Timescale in Thousands of Years Last 10^6 years 10 glacial

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Climate change and severe weather
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Glacial Advance and Retreat: Timescale in Thousands of Years • Last 10^6 years: 10 glacial advances, retreats • Advances last 10^5 years • Retreat much faster than advance, last 10^3 years C ycles in Earth’s orbit affects amount of solar energy received by Earth Postulated in 1920s by Serbian astronomer Milankovitch and supported recently by Greenland ice cores Figure 11.30
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Milankovitch defined changes in Earth’s orbit, tilt and wobble changes in amount of solar radiation received by Earth Glacial Advance and Retreat: Timescale in Thousands of Years Amount of solar radiation at high latitudes during summers determines how much snow remains from winter to next winter, allowing glaciers to grow Figure 11.32
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• Changes in Earth’s orbit: Eccentricity of orbit around Sun: varies every 100,000 years from circular to elliptical (less solar radiation received when elliptical) as dominant control of glacial advance and retreat Tilt of Earth’s axis: 21.5 – 24.5 o off vertical in 41,000 year cycle Precession of tilt: direction of tilt changes (wobble in spin of toy top) in double cycle of 23,000 and 19,000 years Glacial Advance and Retreat: Timescale in Thousands of Years Figure 11.31
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Around 20,000 years ago : Glaciers at maximum extent, covered 27% of today’s land Virtually all of Canada, part of northeastern U.S. Seawater necessary to build glaciers lowered sea level 130 m Current glacial retreat 10% continents still buried under ice If ice melts, sea level would rise 65 m Glacial Advance and Retreat: Timescale in Thousands of Years
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Around 20,000 years ago : Glacial Advance and Retreat: Timescale in Thousands of Years Figure 11.3 Figure 11.33
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Variations within cooling trend: Medieval Maximum : warm period from 1000 to 1300 C.E. Little Ice Age : cold period from 1400 to 1900 C.E. – “epoch of renewed but moderate glaciation” Smaller scale coolings and warmings within Little Ice Age Maunder Minimum : cooler period from 1645 to 1715 C.E. Minimal sunspot activity
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This note was uploaded on 03/22/2009 for the course GEOL 171 taught by Professor Tsoflias during the Spring '08 term at Kansas.

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Ferg_Ch_12_Lecture - Climate change and severe weather Glacial Advance and Retreat Timescale in Thousands of Years Last 10^6 years 10 glacial

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