Milankovitch receive less sunlight in the summer. Short, cool

cycles are cyclical movements related to Earth’s orbit around the Sun.  The orbital effects associated with these
movements operate by changing the seasonal distribution of insolation and the
distance between the Earth and the Sun from time to time.  Such changes alter the amount of solar energy, or
insolation, reaching the outer atmosphere of the Earth.  The three cycles include eccentricity,
axial tilt, and precession.  Milankovitch’s
theory states that these three cycles combined affect the extent of solar heat
that reaches the Earth’s surface and thus, influences climatic
patterns.  Eccentricity describes
how the path of Earth’s orbit around the Sun changes from an almost perfect
circle to an oval shape on a 100,000-year cycle.  The axis is also not upright; it
tilts, with the angle of the tilt varying between 22 and 24 degrees every 41,000
 At the maximum angle,
regions in the extreme upper and lower hemispheres will experience the hottest
summers and coldest winters, and it can be concluded that the
angle of tilt varies the strength of the seasons.  Additionally, precession describes how
the Earth moves around on its axis as it spins.  The axis staggers toward and away from the Sun
due to tidal forces from the Sun and moon over the span of 19,000
to 23,000
which varies the timing of the seasons.  The combination of these small changes in
Earth-Sun geometry change the amount of sunlight each hemisphere receives
annually, where in the orbit the seasons occur, and how intense the
seasonal changes are (Riebeek, 2006).

Milankovitch’s theory helps to explain the timing of the ice ages, which took
when orbital variations caused the Northern Hemisphere around Northern
Europe to receive less sunlight in the summer.  Short, cool summers did not melt all of the snow
from the previous winter, so the snow accumulated year after year, creating a
white surface of increasing area.  The growing
white surface reflected more sunlight back into space, and temperatures continued
to drop even further, until eventually, an ice age would be at its
maximum.  Based on Milankovitch’s
calculations, he predicted that the ice ages would peak every 100,000
and 41,000
with additional occurrences every 19,000 to 23,000 years.  Paleoclimate records show peaks at those exact
intervals.  On land,
there are about three or four recorded ice ages as evidenced by misplaced
boulders and glacial loess deposits; however, ocean core data has
revealed ten ice age events in the last million years, and approximately
100 in the last 2.5 million years (Riebeek, 2006).

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Determining an ice
age in the rock record requires analyzing oxygen isotopes that are trapped in
ocean sediments.  Evidence
supporting Milankovitch’s theory of the timing of ice ages came from a series
of fossilized coral reefs in the South Pacific that formed in a shallow marine
environment during warm interglacial periods.  As ice ages progressed, more water froze
into ice caps and lowered the ocean level—this left the reed exposed.  When the ice caps melted, the ocean levels
rose again and warmed, creating another reef.  During these instances, the peninsula on
which the reefs formed was being simultaneously uplifted by tectonic processes.  Today, these reefs, whose
age was easily determined due to the coral’s decaying uranium, form a series of
steps along the shore of Papua New Guinea, and show the millennia
between ice ages in addition to the defined the maximum length of
each.  The
intervals shown by the corals fell at the exact intervals that Milankovitch
predicted they would


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