Sahara | Can’t Sleep? Explore an Ocean of Sand

The Sahara Desert covers 3.6 million square miles, making it the largest hot desert on Earth and the third largest overall after the polar deserts of Antarctica and the Arctic. Its name comes from the Arabic ṣaḥrāʾ, a broken plural meaning "desert." The episode, from the I Can’t Sleep podcast, presents the Sahara not as a uniform wasteland but as a highly diverse, dynamic region shaped by deep-time climate cycles, unique geography, and human history. The central argument is that the Sahara’s extreme aridity is not a permanent state but one phase in a long-term cycle, and that its present dryness is the result of specific physical and atmospheric mechanisms that can be explained in detail.

The Engine of Aridity: Subtropical High Pressure and Rain Shadows

The Sahara’s dryness is primarily driven by its position under the subtropical ridge, a belt of semi-permanent high pressure. Here, air from the upper troposphere descends, warming and drying as it sinks. This descending airflow suppresses cloud formation and convective overturning, making rainfall virtually nonexistent. The effect is strongest in the eastern part of the desert, the Libyan Desert, which the episode describes as "the sunniest, driest and most nearly rainless place on the planet," rivaled only by the Atacama Desert in Chile.