What is the climate of the Sahara Desert?

The Sahara exhibits great climatic variability within its borders, with two major climatic regimes differentiating along a north-south axis: the desert’s northern latitudes are arid subtropical and have two rainy seasons, while the southern ones, although also arid, are more tropical and have only one rainy season. The southern reaches of the Sahara end in the Sahel, a semiarid buffer zone that separates the desert from the more temperate savanna biomes beyond. A number of other factors affect climatic variability within the Sahara as well: topography does so, as do ocean currents, the latter of which are responsible for the slightly cooler and more humid conditions found on the desert’s western margins. Some scientists estimate that the Sahara became arid about two to three million years ago, while others contend that it happened before this.