Final answer:
The 20,000 year climate cycle in East Africa is driven by Milankovitch cycles, which involve long-term changes in the Earth's orbit and axial tilt, affecting global temperatures and regional precipitation patterns.
Step-by-step explanation:
The 20,000 year climate cycle in East Africa is driven by the Milankovitch cycles, which are long-term fluctuations in the orbit and tilt of the Earth. These natural cycles significantly impact the Earth's climate by altering the amount and distribution of solar energy the Earth receives. In East Africa, these cycles contribute to alternating periods of extreme aridity and very wet conditions, thereby influencing variations in precipitation patterns and regional climate variability. Milankovitch cycles include changes in the eccentricity of Earth's orbit, its axial tilt (obliquity), and precession, which affect global temperatures on geological timescales and can lead to significant ecological and environmental changes, such as the evolution of the Sahara and the transformation of ecosystems.