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As you all know, the earth revolves around
the sun along its orbit. Also, it rotates
about its own axis. Earth’s axis of rotation
is tilted away from the perpendicular to the
plane of its orbit around the sun. At present,
the tilt away from the perpendicular is about
23.5°.
The Milankovitch Theory
Named after the Yugoslav mathematician who
first proposed it, the Milankovitch theory
is the astronomical or orbital theory of climate
variations. The original Milankovitch theory
identifies three types of variations in the
earth's orbit around the Sun which could act
as mechanisms to change the global climate.
The changes include the following.
- Changes in the tilt of the earth’s axis
(obliquity)
- Changes in the shape of earth's orbit
(eccentricity)
- The shifting of the equinoxes (precession)
The three orbital variations together affect
the total amount of sunlight received by the
earth, and distribution of that sunlight at
different latitudes and at different times.
The following graph shows climatic changes
due to orbital variations.
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Changes in climate due to earth's
orbit around the sun
Source: ace.mmu.ac.uk |
It is expected that changes in climate as
a result of orbital variations would occur
in tens of thousands of years. Indeed, the
Milankovitch theory of climate change has
been used to explain the global climate of
the last 2 million years, with changes between
warmer interglacial periods and colder Ice
Ages occurring over a 10,000 year cycle (EAE,
2000).
The
Viking settlement in Greenland... Click
to know
Archaeological records prove that changes
in climate patterns influence the distribution
of civilizations. One good example is
that of the Vikings. About 1000–1100 years
ago, the Vikings migrated from Scandinavia
and moved as far as Greenland. The temperature
there was then higher than it is now,
enabling them to farm in the region.
They also used it as a passage to North
America. Some say that Greenland was actually
‘green’ when the Vikings moved in, which
is how it got its name. After a few centuries,
the temperature began falling, leading
to the Little Ice Age (about 1400–1850).
This caused a decline in agricultural
activities, due to which, the Vikings
were compelled to move further south to
Europe. Thus, the colonies in Greenland
ended.
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What if the earth’s axis were
not tilted? |
If the earth’s axis were not
tilted in this way, there would
be no change of seasons at all.
This will lead to continuous summer
in one region and continuous winter
in another region.
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Initiative
