Using a new computer simulation of Earth's climate, German
scientists say that the Sahara underwent a brutal climate change
about 4,000 years ago.
Over a very short time scale - possibly as short as 300 years -
it went from grasslands with low shrubs to the desert we are
familiar with today. Summer temperatures increased rapidly and
rainfall almost ceased. The change devastated many ancient cultures
and caused those that did survive to migrate elsewhere.
Scientists at the Potsdam Institute for Climate Research say
that the desertification of the Sahara was one of the most dramatic
changes in climate over the past 11,000 years.
The loss of agricultural land to the desert may have been one of
the reasons why early civilisations developed along the valleys of
the Nile, the Tigris and the Euphrates. [This was in the Priora
oscillation, a dry period from circa 3200-2900 BC which
marked the end of a long and wetter, warmer climate period from
about 9,000 to 5,000 years ago, called the Holocene climatic
Slight climate alterations caused by subtle changes in Earth's
orbit around the sun were amplified by a climatic feedback
Some 9,000 years ago the tilt of the Earth's axis was 24.14
degrees; today it is 23.45 degrees. Today, Earth is closest to the
sun in January. Nine thousand years ago, our planet was closest to
the sun at the end of July.
The changes in the tilt of the Earth occur gradually. However,
the interplay of atmosphere, ocean and landmass can react to these
changes in abrupt and severe ways.
The climate model suggests that land use by man was not an
important factor in the creation of the Sahara.