CLIMATE

When the Sahara Was Green

~11,000 to 5,500 years ago

Phanerozoic · Cenozoic · Quaternary · Holocene · Greenlandian

A wobble in the Earth's orbit pulled the summer monsoon north, and the Sahara became grassland with lakes, hippopotamuses, fish and cattle herders who left their paintings on the rock. Then the orbit moved on, the rain went back south, and the largest desert on the planet returned.

Why it matters

The largest landscape change of human history happened without us, and it emptied a region the size of a subcontinent that people had been living in for thousands of years. Whether the drying took a few centuries or three thousand years depends on which lake bed is read, and the difference matters: one is a catastrophe that people fled, the other a slow squeeze over a hundred generations.

Dating & uncertaintyDisputed

That North Africa was green is not in question: lake beds, pollen and rock art all say so. Whether it dried out in a few centuries or over three thousand years depends on the site, and the two readings have not been reconciled.

Sources

1. Kröpelin et al. (2008), Science · Climate-driven ecosystem succession in the Sahara: the past 6000 years
2. Trauth et al. (2024), Nature Communications · Early warning signals of the termination of the African Humid Period
3. Brovkin & Claussen (2008), Science · Comment on Climate-driven ecosystem succession in the Sahara

Earth history as one day

23:59:59.79209 ms before midnight

if Earth’s 4.54 billion years were compressed into a single day