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 that held hippopotamuses and fish, and cattle herders who left their paintings on the rock. Then the orbit moved on, the rain went back south, and the largest hot desert on the planet returned.

Why it matters

Human history has known no landscape change on this scale, and it happened without us: a region the size of a subcontinent, lived in for thousands of years, emptied out. Whether the drying took a few centuries or three thousand years is still argued, and the difference matters: one is a catastrophe 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