Study explains Sahara's periodic green periods

The Sahara Desert was once filled with rivers, giant lakes, and ecosystems supporting hippos, crocodiles, and human communities.

Axial precession, Earth's gradual rotational axis shift, drives orbital variations that bring stronger northern summers every ~20,000 years.

Warmer land strengthens the African summer monsoon, pushing moist air farther north into the Sahara.

Vegetation feedbacks, including darker surface absorption and reduced dust, lock in wet conditions for thousands of years.

A 2023 modelling study led by Edward Armstrong (University of Helsinki) in Nature Communications examines these transformative climate intervals.