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Climate
change mechanisms
Mechanical,
thermodynamical, biological and human factors combined through times to
bring about the climatic changes whose main result is the present Saharan
aridity.
The most important of these factors are those stated by Milutin Milankovitch
in his "astronomical theory" (Milankovitch
1920, 1941). This Serbian mathematician stated that, at a planetary scale,
temporal and geographical climate variations are linked to insolation,
which fluctuates according to the position of the Earth to the Sun. The
succession of the seasons is caused by the angle of the polar axis and
by the annual ecliptic revolution, but the general succession of the glacial
and interglacial periods (corresponding to arid and humid periods in the
Sahara) positioned at much more considerable intervals, is caused by what
could be called "astronomical seasons" linked
to three main factors:
1 -variation in the eccentricity of the Earth orbit,
2 -variation of the obliquity,
3 -precession of the equinox. |
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