Sometime between 11,000 and 5,000 years ago, after the last ice age ended, the Sahara Desert transformed. Green vegetation grew atop the sandy dunes and increased rainfall turned arid caverns into lakes. About 3.5 million square miles (9 million square kilometers) of Northern Africa turned green, drawing in animals such as hippos, antelopes, elephants and aurochs (wild ancestors of domesticated cattle), who feasted on its thriving grasses and shrubs. This lush paradise is long gone, but could it ever return?
In short, the answer is yes. The Green Sahara, also known as the African Humid Period, was caused by the Earth’s constantly changing orbital rotation around its axis, a pattern that repeats itself every 23,000 years, according to Kathleen Johnson, an associate professor of Earth systems at the University of California Irvine.
However, because of a wildcard — human-caused greenhouse gas emissions that have led to runaway climate change — it’s unclear when the Sahara, currently the world’s largest hot desert, will turn a new green leaf.