A desert is defined by an area receiving less than 10 inches of rainfall per year. The Sahara desert is the world’s largest hot desert at 3.6 million square miles, the 2 greatest cold deserts, Antarctica and Arctic, standing at 5.5 million and 5.4 million square miles respectively.
According to a study published in 2018 in the Journal of Climate, the surface area of the Sahara desert has increased by close to 11% in the last one hundred years. Another study postulated that it would continue to grow at the same rate until 2050. It was estimated that 30% of this increase is due to human effect on climate change, the rest being due to natural climate cycles. The Sahara desert influences climate and fertility of very distant regions, notably the Amazon forest, which receives a substantial amount of Saharan dust every year, compensating the loss of nutrients by leaching into the ocean due to rain.
Hot deserts increase in area during the dry season and decrease during the rainy season. There is also a variation on the paleoclimatic time scale. One study stated that the Sahara undergoes a 41,000 year cycle due to the change in the tilt of the Earth between 22 degrees and 22,5 degrees, and that in 15,000 years or so, it’ll be lush and green again. 867
The angle affects the amount of albedo, i.e. the amount of solar radiation that is reflected back into space. Less radiation reflected back means more retained thus increased temperature which drives the monsoon systems farther towards the poles, increasing the area of the rain belt, thus greening the Sahara.
Climate model studies propose that if humans continue to elevate the temperature of the Earth by adding more carbon into the atmosphere, this greening of the Sahara could have a butterfly effect on a massive scale, reducing the amount of Saharan dust in the atmosphere, further increasing the amount of solar radiation retained on Earth, warming up the ocean at the place where hurricanes form that end up beating down on the East Coast of the United States, thus causing more instability at that end.
Will the Sahara continue expanding or will it become lush and green, causing monster hurricanes to unleash against the US? One thing scientists agree upon is that we must adapt to climate change by applying agroforestry in the Sahel, where farmers who integrate trees and shrubs into normal farming practices, along with soil and water conservation techniques, have managed to reclaim villages from the advance of the desert. This method makes good use of the change in the Sahara rainfall which seems to be less frequent but more intense. Moreover, reducing runoff and increasing water infiltration into the soil by greater vegetation cover recharges aquifers. Another project is to install large scale wind and solar farms in the Sahara, providing clean energy, reducing the amount of greenhouse gasses and promoting increased precipitation in the area.
For now, the Sahara is increasing in size, due mostly to its natural cycle but partly to human activity. Models for the future differ, but best be prepared!
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