EPS 201 CLIMATE 3 - Lecture Notes Milankovich Cycles...

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Lecture Notes – April 14, 2009 Milankovich Cycles Changes Controlling Short-Term Climate Changes Lecture begins with an analysis of a graph in which the d 18 O concentration in biosediments varies over time, indicating a cyclic change in temperature/ice volume. From this we can see that there are three cycles in the climate on the following intervals: 1-5 million years 100,000 years 40,000 years 20,000 years Folks prior to Milankovich knew that there were changes in the Earth’s orbit that might have a reason for these cycles. Aside from angle of insolation is not the only cause of variations of climate. If we view the solar system from above, we can see that the Earth’s orbit is slightly elliptical – the shape of the orbit, however, changes over long periods of time. It turns out that because of the gravitational attraction of the large planets, there is an effect on the shape of the orbit of earth. Dr. Maya puts up three images showing eccentricity, obliquity, and precession. Eccentricity is a change in ellipticity, meaning that sometimes the orbit is more elliptical than at other times. Thus, there are orbits in which the earth can come closer to the sun, or orbits where the earth can be farther from the sun at other times. Obliquity refers to the change in the angle of the axis, which varies from 22.1° to 24.5° in the image she displays. This has an effect on the angle of insolation. Precession refers to the change in orientation of the axis, which looked at from “above” (i.e., looking down on the North Pole) would describe a counter-clockwise circle.
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Handout includes an image highlighting eccentricity – shows how in the more elliptical orbit there is a greater seasonal difference than in the less elliptical orbit, which demonstrates a lesser seasonal difference. OK – the gist of what Maya says here is that the orbit with greater elliptical shape will allow the formation of less ice, and the orbit with lesser elliptical orbit will allow the formation of more ice. This is because there is a greater variation in temperature in the more elliptical orbit, and a lesser variation in temperature in a lesser elliptical orbit. Greater obliquity accentuates the tilt of the earth. When you accentuate the tilt, there is a greater temperature contrast between seasons. Therefore, the lesser obliquity is responsible for greater ice building. Greater obliquity is responsible for less ice building, because it accounts for a greater variation in temperature between seasons. Obliquity is a result of gravitational action of the moon. This occurs on a 40,000 year cycle, that also occurs within a 1.4 million year cycle, and perhaps another cycle of about 5 million years in terms of extremes of obliquity. Precession refers to the circular orientation of the axis of the earth with respect to
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This note was uploaded on 02/02/2011 for the course EPS 201 taught by Professor Mayaelrick during the Spring '09 term at New Mexico.

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EPS 201 CLIMATE 3 - Lecture Notes Milankovich Cycles...

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