The Sahara Desert wasn't always the arid, desolate landscape we know today. Between 14,500 and 5,000 years ago, the region was unrecognizable. During an unusually wet period known as the African Humid Period, it transformed into a lush tropical savanna. People roamed this green land for thousands of years before it was once again submerged by sand.
[Sahara Desert]
The Sahara Desert is located in northern Africa, stretching from the Red Sea in the east to the Atlantic Ocean in the west and north to the Atlas Mountains and the Mediterranean Sea. It stretches across the northern part of the African continent, encompassing 11 countries: Egypt, Sudan, Libya, Chad, Tunisia, Algeria, Niger, Morocco, Western Sahara, Mali, and Mauritania.
[Sahara Rock Art]
The Sahara rock art, like a "Records of the Grand Historian" or "Book of Han," records a seemingly fragmented yet ultimately coherent past. Sahara rock art isn't confined to a single, narrow region; it's spread throughout the entire Sahara Desert. Rock paintings have been discovered from Egypt to Sudan, from Algeria to Morocco, and even in Mozambique in southeastern Africa. The stories recorded in these rock paintings can be seen as the story of the entire Sahara.
Many rock paintings depict horses. Horses are animals that follow water and grass. Their presence here suggests that the Sahara long ago had vast grasslands or oases. The rock paintings also depict buffalo, galloping antelope, massive elephants, leisurely hippos, giraffes, and more. Thousands of buffalo frolic in the paintings, splashing water everywhere, creating a vivid and lifelike scene. The discovery of so many animals in the Sahara demonstrates the vastness of the grasslands.
The earliest of these rock paintings dates back over 10,000 years, while the latest is roughly 4,000 years old. This means that 4,000 years ago, the Sahara was still lush and green, and 10,000 years ago, it was a vast, warm and humid grassland with abundant rainfall.
Will there be a chance for it to become green again?
- Regarding the reasons for the Sahara's oasis and desert, aside from the human influence mentioned above, most people believe the shift in Earth's axial tilt is due to changes in its tilt.
Gavin Schmidt, a meteorologist at NASA's Goddard Institute for Space Studies, has stated that approximately 8,000 years ago, Earth's orbital tilt was 24.1 degrees, but today it has shifted to 23.5 degrees, altering the way solar radiation penetrates the atmosphere.
- This shift caused cyclical variations in the African monsoon climate, controlling the intensity and northward penetration of monsoon rainfall, directly transforming the then extremely arid desert into an oasis.
This period is known as the African Humid Period (AHP).
It is generally believed that the increased solar radiation received by the mid- and high-latitudes of the Northern Hemisphere due to the precession of the equinoxes was the primary cause of the AHP.
During this period, African monsoon rainfall increased by at least 17%, and if ocean feedback is included, the increase is 50%.
- With increased rainfall, symbols of life, such as lakes, rivers, and green plants, naturally appeared in the Sahara. However, as mentioned, the tilt of the Earth's axis is constantly changing, meaning this phenomenon cannot remain constant.
Katherine Johnson of the University of California, Los Angeles, has argued that slight shifts in Earth's tilt cause a gradual change in solar radiation. As the monsoon winds decrease, vegetation also begins to disappear. In the macroscopic natural world, this translates to a sudden shift in landscape: from a green Sahara to a desert Sahar.
And this happened in just 200 years!
According to the African Humid Period cycle, the transition between desert and oasis occurs every 23,000 years. Historical lake level data across much of Africa indicates the continent's universality of this pattern, meaning a return to a green Sahara is very likely in the future.
