Humans may have played an active role in the Sahara’s desertification. This is the conclusion of new research exploring the conversion of the Sahara from a lush, green landscape 10,000 years ago, to the waterless conditions found today.
Scientists trying to understand ecological and climate tipping points have long targeted the desertification of the Sahara for study. In a paper recently published in Frontiers in Earth Science, the archeologist Dr. David Wright from the Seoul National University challenges the conclusions of most studies done to date that indicate that the major driving forces were natural changes in vegetation, or changes in the Earth’s orbit.
Wright explained that there are long established theories in East Asia of how Neolithic populations had changed the landscape so dramatically that monsoons stopped progressing so far inland. He also noted in his paper that evidence of human driven climatic and ecological change has been documented in New Zealand, Europe and North America. Wright is of the opinion that similar scenarios could apply to the Sahara.
To test his theory, Wright looked over archaeological evidence documenting the first appearances of pastoralism across the Saharan region. This was then compared to records showing the spread of scrub vegetation, which is an indicator of an ecological change towards desert like conditions. His hypothesis was confirmed. Pastoral communities began to appear from approximately 8,000 years ago in the regions surrounding the Nile River and then spread westward. In each case, this happened at the same time as when scrub vegetation increased.
The region’s ecology was severely affected by growing agricultural addiction. As the introduction of livestock resulted in more vegetation being removed, it increased the amount of sunlight that reflects off the earth’s surface (called the albedo) of the land. This in turn affected atmospheric conditions to such a degree that monsoon rainfall was reduced. The weakening monsoons caused further vegetation loss and desertification, stimulating a feedback loop that eventually spread over the entire modern Sahara.
Although there is still much work still to do to fill in the gaps, Wright believes that a wealth of information lies hidden beneath the surface. He notes that at this time, there were lakes everywhere in the Sahara, and these will contain the records of the vegetation changing.
Wright would like to drill down into these former lake beds to obtain the vegetation records, and then look at the archaeology to see what people were doing there. He noted that to model the effect of vegetation on climate systems is very difficult and it is up to ecologists and archaeologists to uncover the data. This will help them to make models that are more sophisticated.
Despite the fact that these events took place several thousands of years ago, it is easy to see the implications of humans being responsible for climatic and environmental degradation. With around 15% of the world’s population already living in desert regions, Wright feels that the implications of how humans change ecological systems will have a direct impact on whether we will be able to survive indefinitely in arid environments, or not.