Using a new computer simulation of Earth's climate,
German scientists in 1999 announced the finding that the Sahara
underwent a brutal climate change around 2000 BC.
Over a very short time scale - possibly as short
as three hundred years - it went from grassland 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
Scientists at the Potsdam Institute for Climate
Research said 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 a period known as the Priora oscillation, a dry period from
circa 3200-2900 BC which marked the end of a long, wetter,
warmer climate period from about 9,000 to 5,000 years ago, called
the Holocene climatic optimum.
Slight climate alterations caused by subtle changes
in the Earth's orbit around the sun were amplified by a climatic
feedback mechanism. Around 7000 BC, 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. This particular climate model
suggested that land use by man was not an important factor in the
creation of the Sahara. They were simply victims of extreme climate