Sahara

The Sahara is the largest hot desert in the world and the third-largest desert overall, after Antarctica and the Arctic. It stretches across much of North Africa, from the Atlantic Ocean in the west to the Red Sea in the east, and from the Mediterranean coast in the north to the Sahel region in the south. Its name derives from an Arabic word meaning "desert."

Far from being a single uniform expanse of sand, the Sahara is a varied landscape of rocky plateaus, gravel plains, mountains and only a minority of sand dunes. It is one of the driest and harshest environments on Earth, yet it has been crossed and inhabited for thousands of years.

Extent and geography

The desert covers roughly nine million square kilometres, an area close to that of the entire United States. It spans numerous countries, including Algeria, Egypt, Libya, Morocco, Sudan, Chad, Niger and Mali. Its highest point is a volcanic peak in the Tibesti Mountains of Chad, and its lowest, driest areas lie far below sea level in Egypt.

Sand seas, called ergs, cover only a fraction of the surface but create the classic dune landscapes people associate with the desert. Much of the Sahara is hamada, a rocky stony plain, or reg, a gravel plain.

Climate and change

The Sahara is extremely arid, with high temperatures by day and cold nights, because dry air and clear skies allow heat to escape quickly after sunset. Rainfall is scarce and irregular; some areas may go years without significant rain. Hot, dusty winds frequently blow across the region.

The desert has not always been so dry. Geological and archaeological evidence shows that in the past, parts of the Sahara were much wetter, with lakes, rivers and savanna supporting animals such as hippos and crocodiles. This "green Sahara" period, sometimes called the African Humid Period, ended as the region dried out over thousands of years, partly due to shifts in Earth's orbit. Rock art across the desert depicts giraffes and other animals that no longer live there, offering evidence of that greener past.

People and cultures

Despite its harshness, the Sahara has long been home to peoples such as the Tuareg, Berbers and various Arab and Sahelian groups. They developed knowledge of wells, oases and navigation that made life and travel possible. Oases, fed by underground water, support settlements, date palms and trade.

Historically, the Sahara was not a barrier but a bridge. Trans-Saharan trade routes carried gold, salt, textiles and enslaved people between sub-Saharan Africa and the Mediterranean world for many centuries. Salt, mined in the desert, was especially valuable, and caravan towns grew rich as trade hubs.

Resources and modern life

Today the Sahara contains valuable resources, including oil and natural gas in several countries, as well as minerals and large reserves of underground water from ancient aquifers. Solar energy potential is enormous because of the near-constant sunshine. Yet these resources raise difficult questions about sustainability, since much of the water is non-renewable "fossil water."

The desert also borders the Sahel, a semi-arid belt to the south where desertification — the spread of desert-like conditions — has been a concern linked to drought, overgrazing and climate change. The idea of a "great green wall" of trees across Africa aims to slow that spread.

Oases, water and travel

Water is the key to life in the Sahara. Where underground aquifers reach the surface, oases appear and support towns, farms and palm groves. Wells and knowledge of their locations made long-distance travel possible. Traditional caravans crossed the desert in stages, travelling at night or in cooler hours to limit exposure, guided by experienced navigators who read stars, winds and terrain.

Camels were central to this world. Adapted to extreme heat and able to travel long distances with little water, they carried goods across routes that linked West Africa to the Mediterranean and the Middle East. These routes spread not only merchandise but also ideas, languages and religion, helping Islam and Arabic culture reach vast areas of North and West Africa.

Life adapted to dryness

Plants and animals in the Sahara survive through remarkable adaptations. Some plants store water in fleshy tissues or have deep roots; others complete their life cycle quickly after rare rain. Animals are often nocturnal, sheltering from daytime heat, and many obtain moisture from food rather than drinking. Lizards, foxes, antelope and numerous insects thrive despite the harsh conditions.

Human adaptations are cultural as well as biological: clothing and building styles are designed to manage heat and sunlight, and social customs are shaped by the demands of living in a sparse, mobile environment.

Common misconceptions

A common myth is that the Sahara is all sand and dunes; in fact dunes cover only a minority of its area, and rocky and gravel plains dominate. Another misconception is that it is completely lifeless, when it supports plants, animals and human communities adapted to the dry conditions. Finally, the desert is sometimes imagined as unchanging, but it has shifted dramatically over geological and historical time.

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