At some point in history (between 11,000 and 5,000 years after the last Ice Age) vegetation grew over the Sahara desert. The sandy dunes were teeming with plants, and the rains turned the most popular caves in the Sahara into lakes. In fact, its 9 million square kilometers turned green and some species, such as hippos, elephants or antelopes, fed on the grasses and shrubs that grew in the desert.
Although this happened thousands of years ago, the truth is that the Sahara could turn green again. According to Kathleen Johnson, professor of Earth systems at the University of California, the African Humid Period (also known as the Green Sahara) was caused by the rotation of the Earth around its axis, since the Earth, every 23,000 years, undergoes a wobble in its orbit and on its axis.
This wobbling of the Earth causes the wind and rain to move to other latitudes. In this case, the monsoons (seasonal winds that cause the displacement of large amounts of water) would discharge more to North Africa, on the Sahara, instead of falling on sub-Saharan Africa. However, due to climate change and greenhouse gases, scientists do not know when the Sahara, (currently the largest hot desert in the world), will be transformed into a river forest.
Tilt of the earth
About 8,000 years ago, the Earth’s tilt changed from about 24.1 degrees to 23.5 today. This variation made a huge difference, as the Northern Hemisphere now leans farther from the sun during the winter months. However, during the Green Sahara the northern hemisphere was closer to the sun in summer.
This caused an increase in solar radiation (that is, heat) in the Earth’s northern hemisphere and consequently increased the African monsoon. The increase in humidity transformed the previously sandy Sahara into a land covered with grass and bushes.
However, the Earth’s orbit was rearranged again, so this climate did not last more than two centuries. And, although the change in solar radiation was gradual, the landscape changed suddenly. Scientists currently expect the Green Sahara to reappear in about 10,000 years, although they cannot predict how greenhouse gases will affect this natural climate cycle.
