Using a new computer simulation of Earth's climate,
German scientists in 1999 announced the finding that the Sahara
underwent a brutal period of climate change around 2000 BC.
Over a very short time scale - possibly as little
as three hundred years - it went from grassland with low shrubs to
the desert with which we are familiar today. Summer temperatures
increased rapidly and rainfall almost entirely ceased. The change
devastated many ancient cultures and caused those that did survive
to migrate elsewhere.
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 eleven thousand
The loss of agricultural land to the growing 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 between
about 3200-2900 BC which marked the end of a long, wetter, warmer
climate period between about 7000-3000 BC, called the Holocene
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 at
its closest to the sun in January. Nine thousand years ago, the
planet was at its 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 the victims of extreme climate
It would not have been the first time. Similar
drastic changes in climate in the Sahara (and Negev Desert) have
also been dated to around 130,000 years ago during separate research