Was the Sahara Desert ever green in colour?  

What comes to your mind when you hear the word Sahara? Most of us picture the unrelenting sun, sloshing sand, and oases that are difficult to find. But 5000-11,000 years ago, the world's largest hot desert was not so harsh and uninhabitable. It was green, lush, alive, and punctuated by lakes, rivulets, grass fields, and thick forests. Could this paradise ever come back? Come, join us in our sojourn through the Sahara Desert and explore it!  

Green Sahara  
Sahara, the gigantic desert, was green and lush during the African Humid Period (between ca. 14,500 to 5000 years ago). Its desertification started around 7000 years ago. The Earth’s orbital precession turned this green bounty into the hottest desert. Earth’s orbital tilt towards the sun began around 8000 years ago; it changed from 24.1 degrees to 23.5 degrees. When the tilt decreased, the northern regions of Africa stopped getting heavy monsoons, which are important for the ecosystem and greenery. With their annual water supply steadily cut off, plants couldn’t survive, and the Sahara started turning into a desert. This transformation took around 200 years. The increase in the solar radiation also resulted in seasonal wind shift over the Sahara region. 

According to Kathleen Johnson, associate professor of Earth systems at the University of California Irvine, the Earth's cyclical orbital revolution around its axis repeats Green Sahara every 23,000 years. A 2019 study in the journal Science Advances found that the region switches between being a brutal desert and a lush green oasis every 20,000 years. The researchers studied marine sediments deposited with Sahara dust 240,000 years ago. They discovered that the dry and green cycles of the Sahara matched with the minute variations in the tilt of the Earth's axis. The next Northern Hemisphere summer shift is when green Sahara could reappear. According to studies, it may happen again in 10,000 years from now (in A.D. 12000 to A.D. 13000) 

Earth’s largest and hottest desert 
The Sahara Desert is the third largest desert in the world after the Arctic and Antarctica. It occupies a gigantic area of 9,200,000 square kilometres in North Africa. The Sahara has the highest recorded temperature of 58°C, making it the world’s hottest desert. However, the night-time lows can be -6°C due to a sharp drop in temperature. Mountains in the region frequently experience snowfall.  

Sand dunes and saltwater 
Although the Sahara Desert contains many different geographical features, it is famous for its sand dune fields, as frequently shown in films. It comprises everything from rocky, desolate plateaus, to salt flats, mountains, and dry valleys. Except for the Nile River, all of the rivers and streams in the Sahara are seasonal. In fact, 70% of the desert contains gravel, and only 30% is sand!  

Among the 20 lakes in this desert, most are saltwater lakes except for Lake Chad which is a freshwater lake. Emi Koussi, a volcano in the Tibesti Mountains, is the highest point in the Sahara at 3,415 metres. At 436 feet below sea level, the Qattara Depression is the deepest point in the Sahara. The Hoggar Mountains, Tibesti Mountains, Saharan Atlas, Adrar des Iforas, and the Red Sea hills are some of the other mountain ranges in the region. 

Flora and fauna of Sahara 
Due to unfavourable atmospheric conditions, only 2 million people live in Sahara. But Sahara is home to more than 500 species of plants, 70 species of mammals, 90 species of birds, 100 species of reptiles, and other arthropods. Due to water scarcity, vegetation is likewise scarce but thrives near oases and reservoirs. Date palms, tamarisks, and acacia plants survive such a scorching temperature because of their deep-rooted ability to soak water. The cactus is a typical desert plant of the Sahara. 

The Sahara is still present despite numerous disasters. The inhabitants continue to dig deeper wells and loot the declining vegetation in the same destructive ways that their forebears did. It's uncertain when the Sahara, the largest hot desert in the world, will turn a new leaf.