Sahara

The Sahara stretches across northern Africa between the Atlantic Ocean to the west, the Mediterranean Sea and Atlas Mountains to the north, the Red Sea to the east, and the semiarid Sahel to the south. Encyclopaedia Britannica estimates its area at about 8.6 million square kilometres, while noting that mapped boundaries and area vary as the desert's margins expand and contract. It is the world's largest hot desert, but it is not a single political or cultural region: it crosses parts of several countries and contains markedly different landscapes.

The Sahara is not uniformly sandy. Its surface includes broad gravel plains, bare-rock plateaus, mountain massifs, salt-rich basins, seasonal lakes and channels, and sand sheets and dunes. Britannica estimates that sand sheets and dunes cover about one-quarter of the desert. Water is unevenly distributed: the Nile runs along the eastern margin, the Niger crosses part of the southwest, and networks of temporary streams drain after rain. Groundwater sustains many oases, where springs, wells and irrigated plots create small inhabited landscapes within the arid region.

Conditions vary across the Sahara. Rainfall is scarce overall, but the northern and southern portions have different seasonal patterns, and elevation and ocean influence create local contrasts. The Sahel forms a transitional, semiarid belt rather than a sharp line between desert and savanna. Plants and animals persist through adaptations to dryness and are especially associated with better-watered highlands and oases. The region was not always as arid as it is today: geological and archaeological evidence, together with climate modelling, indicates repeated North African Humid Periods when vegetation, lakes and rivers expanded. A 2023 Nature Communications modelling study simulated 20 such periods over the past 800,000 years; it links their pacing mainly to changes in Earth's orbital precession and their strength in part to eccentricity and glacial ice-sheet conditions. These are model results in an active field of research, not a precise forecast of future greening.

People have inhabited the Sahara for millennia, adapting livelihoods to changing water and pasture. Historical patterns include mobile pastoralism, cultivation around oases and travel along trade routes; contemporary communities also engage with towns, transport, extraction and other modern economies. These ways of life are diverse, and the desert should not be treated as culturally uniform. Research on Algerian oases describes them as places where biological and cultural diversity intersect, while also noting that water abstraction, environmental degradation and social change can place pressure on oasis systems.

Strong winds lift mineral dust from North Africa into the atmosphere. NASA describes the Sahara as Earth's largest source of airborne dust and documents plumes carried over the Atlantic; depending on their concentration and atmospheric conditions, dust particles can also affect rainfall from tropical cyclones. These long-distance movements link the Sahara's dry landscapes to weather processes far from the region.

Over the past 800,000 years: a 2023 climate-model study simulates repeated North African Humid Periods, with their timing associated chiefly with orbital precession and their amplitude influenced by eccentricity and glacial conditions. About 6,000 years ago: the end of the most recent African Humid Period was followed by continuing aridification across North Africa, as described in research on Saharan oases and their changing environments.