Prehistoric Africa

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 which 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 years.

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 climatic optimum.

Feedback mechanism

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 change.

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 in 2007. The Late Palaeolithic Khormusan industry of the Nile Valley appeared around 30,000 BC during another grasslands-to-sand shift.

The Sahara has undergone a gradual transition from sweeping grassland to dessicated sand on more than one occasion, notably around 30,000 BC (and again around 2000 BC)

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