Major Deserts of the World
Major Deserts of the World : Antarctica
| Arabian | Atacama
| Chihuahuan | Gobi
| Great Basin | Great
Victoria | Highlands
of Iceland | Kalahari
| Monte | Patagonian
| Sahara | Taklamakan
| Thar
Sahara Desert
The Sahara is the world's largest hot desert, and second largest desert after Antarctica. At over 9,000,000 square kilometres (3,500,000 sq mi), it is almost as large as the United States, and is larger than the 48 contiguous states. The Sahara defines the borders of North Africa and has an intermittent history that may go back as much as 2.5 million years.
Climate
The climate of the Sahara has undergone enormous variation between wet and dry over the last few hundred thousand years. During the last ice age, the Sahara was bigger than it is today, extending south beyond its current boundaries. The end of the ice age brought wetter times to the Sahara, from about 8000 BC to 6000 BC, perhaps due to low pressure areas over the collapsing ice sheets to the north.
The Sahara has one of the harshest climates in the world. It has many strong winds that blow from the north-east. Sometimes on the border zones of the north and south, the desert will receive about 25 cm (10 in.) of rain a year. The rainfall happens very rarely, but when it does it is usually torrential when it occurs after long dry periods, which can last for years. Daytime temperatures can be 58 °C (136 °F), but freezing temperatures aren't uncommon at night, reaching as low as -6 °C (22 °F).
Once the ice sheets were gone, the northern part of the Sahara dried out. However, not long after the end of the ice sheets, the monsoon which currently brings rain to the Sahara came further north and counteracted the drying trend in the southern Sahara. The monsoon in Africa (and elsewhere) is due to heating during the summer. Air over land becomes warmer and rises, pulling in cool wet air from the ocean. This causes rain. Paradoxically, the Sahara was wetter when it received more solar insolation in the summer. In turn, changes in solar insolation are caused by changes in the Earth's orbital parameters.
By around 2500 BC, the monsoon retreated south to approximately where it is today, leading to the desertification of the Sahara. The Sahara is currently as dry as it was about 13,000 years ago. These conditions are responsible for what has been called the Sahara Pump Theory.
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