Introduction The Milankovitch Theory Processesx x x Eccentricity
Obliquity Precession
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INTRODUCTION Milutin Milankovitch
Serbian astrophysicist best known for developing one of the most
significant theories relating Earth motions and long-term climate
change
dedicated his career to developing a mathematical theory of
climate based on the seasonal and latitudinal variations of solar
radiation received by the Earth ( The Milankovitch Theory )
Milutin Milankovitch
built his theory from previous work done by J.A. Adhemar and
James Croll 1842 - Adhemar explained glacial climate using only
precession 1864 - Croll wrote about orbital change and the ice of
the Ice Ages
using both the eccentricity cycle and the precession cycle 1875
- he took into account obliquity (tilt of the axis) cycle
being a mathematician, took Croll's work and set out to develop
a mathematical theory of climate change
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The Milankovitch Theory
an explanation of long term climate change
it states that as the Earth travels through space around the
sun, cyclical variations in three elements of Earth-sun geometry
combine to produce variations in the amount of solar energy that
reaches Earth
Three elements:1. Eccentricity
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2. Obliquity
3. Precession
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ECCENRICITY
is a term used to describe the shape of Earth's orbit around the
sun variation of Earth's orbit around the sun ranges from 0.0005 to
0.0607
time frame for the cycle is approximately 98,000 years impact of
the variation is a change in the amount of solar energy from
perihelion to aphelion
at present, Earth's eccentricity is 0.016 about 6.4 percent
increase in insolation from July to January
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ECCENRICITY
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OBLIQUITY
the variation of the tilt of the earth's axis away from the
orbital plane varies between 22.1o and 24.5o and the average is
23.5o
changes on a cycle taking approximately 40,000 years
OBLIQUITY
as this tilt changes, the seasons become more exaggerated
"the more tilt means more severe seasons - warmer summers and
colder winters; less tilt means less severe seasons - cooler
summers and milder winters." (Kaufman, 2002)
an increase of 1o in obliquity, the total energy received by the
summer hemisphere increases by approximately 1% currently the
motion is 1.4 km/century as the obliquity decreases 46.85
inches/century
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OBLIQUITY
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PRECESSION
the change in orientation of the Earth's rotational axis the
cycle takes about 19,000 - 23,000 years two factors:
a wobble of the Earth's axis turning around of the elliptical
orbit of the Earth itself
PRECESSION
it affects the direction of the Earth's axis
the change in the axis location changes the dates of perihelion
and aphelion
currently, the Earth is closest to the sun in the northern
hemisphere winter
another consequence of precession is a shift in the celestial
poles
5000 years ago the North Star was Thuban in the constellation
Draco currently the North Star is Polaris in the constellation Ursa
Minor
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PRECESSION
Milankovitch was able to formulate a comprehensive mathematical
model that calculated latitudinal differences in insolation and the
corresponding surface temperature
assumed that radiation changes in some latitudes and seasons are
more important to ice sheet growth and decay than those in
others
German Climatologist Vladimir Koppen
summer insolation at 65 degrees North as the most important
latitude and season to model
correlation of the three variations
for about 50 years, Milankovitch's theory was largely ignored
1976 - a study published in the journal Science examined deep-sea
sediment cores
Milankovitch's theory did in fact correspond to periods of
climate change
...orbital variations remain the most thoroughly examined
mechanism of climatic change on time scales of tens of thousands of
years and are by far the clearest case of a direct effect of
changing insolation on the lower atmosphere of Earth. (National
Research Council, 1982)HOME
