17ClimateObservations

17ClimateObservations - ESM 203 Climate Change Observations...

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ESM 203: Climate Change— ESM 203: Climate Change— Observations Observations Fall 2007
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2 What makes a climate model  What makes a climate model  believable? believable? Crucial question in distinguishing natural from  anthropogenic variability Ability to explain Long-term trends in global climate Spatial variability in climate Response to short-term forcing Paleoclimatology and historical climatology Record of past changes
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Climate change at time scale 10-100  Climate change at time scale 10-100  million years million years Reminder from Tom’s lecture on Global Tectonics Slide #20, 11/01/2007, Solid Earth 1 Fundamental differences between continental crust  and ocean crust: lithology, density, elevation Global distribution of continents and ocean  basins affects patterns of net radiation and  ocean circulation 3
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Sea floor Ages Sea floor Ages http://www.ngdc.noaa.gov/mgg/image/crustageposter.jpg
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5 Climate change at scales 10 thousand to a  Climate change at scales 10 thousand to a  few million years: the Milankovitch (1920)  few million years: the Milankovitch (1920)  hypothesis hypothesis Long-term variations in climate depend on  seasonal and geographic variations in solar  radiation, which are caused by orbital variations
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6 Orbital causes of climate variability Orbital causes of climate variability Eccentricity period 95–125 kyr orbit varies between more  eccentric and more circular Obliquity period 41 kyr tilt of Earth’s axis varies  from 21.8–24.4 o Precession period 21-23 kyr date of perihelion cycles  through calendar 147M km 152M km Jan 5 July 4 There is also a  100 kyr variation  in the orbital  inclination, 2°+  from the plane of  the ecliptic
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7 Long-term variability in ocean  Long-term variability in ocean  δ δ 18 18 O: why  O: why  the shift from 41 Kyr to 100 Kyr? the shift from 41 Kyr to 100 Kyr? 41 Kyr cycle dominated 1.5- 2.5 million years ago 100 Kyr cycle dominated in  last million years Glacial Cycles and Astronomical  Science, 277,  215-218, July 11, 1997
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8 Synchronous behavior of the ice sheets  Synchronous behavior of the ice sheets  despite asynchronous radiation forcing  despite asynchronous radiation forcing  P. U. Clark, R. B. Alley, & D. Pollard,
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This note was uploaded on 08/06/2008 for the course ESM 203 taught by Professor Dozier,dunne during the Fall '07 term at UCSB.

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17ClimateObservations - ESM 203 Climate Change Observations...

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