The Sahara is the world's largest hot desert, spanning approximately 9.2 million square kilometers (3.6 million square miles) across North Africa. It stretches from the Red Sea in the east to the Atlantic Ocean in the west, and from the Mediterranean Sea in the north to the Sahel region in the south. The Sahara covers about 31% of Africa's land area and includes parts of twelve countries: Algeria, Chad, Egypt, Libya, Mali, Mauritania, Morocco, Niger, Sudan, Tunisia, Western Sahara, and a small portion of Eritrea. Its name derives from the Arabic word ṣaḥrāʾ, meaning "desert."
The Sahara's landscape is diverse, featuring vast sand seas (ergs) like the Grand Erg Oriental and Grand Erg Occidental, gravel plains (reg), rocky plateaus (hamadas), and mountain ranges such as the Ahaggar Mountains in Algeria and the Tibesti Mountains in Chad. Notable features include the Qattara Depression in Egypt, one of the lowest points on Earth at 133 meters below sea level, and oases like Siwa Oasis. The desert's climate is hyper-arid, with annual rainfall often less than 25 mm in central areas, though northern and southern fringes receive up to 200 mm during rare wet seasons. Daytime temperatures can exceed 50°C (122°F), with record highs of 58°C (136.4°F) recorded near Tripoli, Libya, while nights can drop below freezing. The subtropical high-pressure ridge prevents cloud formation, leading to intense solar radiation and minimal vegetation outside oases.
The Sahara is divided climatically: the north is Mediterranean-influenced with two rainy seasons, while the south is more tropical with one. Ocean currents, like the cool Canary Current, moderate western coastal areas, creating fog deserts in places like the Namib transition zones, though the core remains extremely dry.
Life in the Sahara is sparse but resilient. Vegetation includes drought-resistant species like the date palm (Phoenix dactylifera) in oases, acacias, and grasses in wadis (seasonal riverbeds). Endemic plants such as the Saharan myrtle (Myrtus nivellei) thrive in mountainous regions. Fauna adapted to the harsh conditions includes the fennec fox, addax antelope, Saharan cheetah, and Barbary sheep. Birds like the spotted sandgrouse migrate across the desert, while reptiles such as the horned viper and various scorpions are common. The Sahara supports about 70 mammal species, 90 resident bird species, and over 500 plant species, many confined to refugia like the Hoggar Mountains.
The Sahara has not always been a desert. During the African Humid Period (circa 11,000 to 5,000 years ago), it was a savanna with lakes, rivers, and grasslands, supporting megafauna like elephants, giraffes, hippos, and crocodiles. Human populations, including hunter-gatherers and early pastoralists, left rock art in sites like Tassili n'Ajjer in Algeria, depicting this "Green Sahara." Archaeological evidence, including fish hooks and cattle bones, indicates settlements around ancient lakes like Megalake Chad.
Desertification began around 5,500–5,000 years ago due to changes in Earth's orbital precession, weakening the West African monsoon and causing vegetation feedback that amplified aridity. This process, occurring over centuries rather than abruptly, displaced populations southward into the Sahel and Nile Valley, influencing the rise of ancient civilizations like Ancient Egypt. The Sahara has cycled between wet and dry phases every 20,000–23,000 years, aligned with Milankovitch cycles, with the last humid period ending in the mid-Holocene.
Human history in the Sahara includes trans-Saharan trade routes from the 8th century CE, facilitating the exchange of gold, salt, ivory, and slaves between Sub-Saharan Africa and the Mediterranean world. Berber and Arab nomads, such as the Tuareg, dominated these caravans, establishing empires like the Ghana Empire and Mali Empire. Rock paintings and petroglyphs, dating back 12,000 years, provide insights into prehistoric life. In modern times, the Sahara is home to about 2.5 million people, primarily nomadic or semi-nomadic groups like the Bedouin and Tuareg, who herd camels and goats. Challenges include desertification, exacerbated by climate change, and conflicts over resources.
Exploration milestones include the crossing by Alexander Gordon Laing in 1826 and the first automobile traversal in 1923. Today, the Sahara faces environmental threats, with expanding dunes threatening oases and increasing temperatures altering migration patterns.
Sources consulted: Wikipedia: Sahara, Britannica: Sahara Desert, Live Science: The Sahara, Phys.org: Sahara Climate Cycles.