Before the Sahara was green and covered with water.
Lowering the temperature led to the fact that the winds stopped bringing precipitation to the Northern part of Africa in the same volume, and Sugar from blooming oasis turned into a desert.
Researchers from the US found out why the Sahara was green and covered with water when the climate was even warmer than it is now. The corresponding article was published in the journal Science Advances.
The researchers analyzed traces of dust, which the winds from the Sahara bring in continental North America and the Bahamas.
How they managed to figure out 5 000-11 000 years ago this dust was 40-50 percent less than now. During this period the climate was much warmer than today: this will be in the XXII century, if the warming will not stop.
About 5,000 years ago, it was cold, which made the climate of the world is close to its status in the XX century.The planet as a whole has become colder, and Sugar, five thousand years ago is covered by Savannah and lakes, began to desert.
Scientists set out to understand how cold did the once flourishing region devoid of vegetation. To do this, they built a climate model that takes into account the effect of changes in the amount of Saharan dust in the air. They did that with modern quantities in the air over the Atlantic, the sand reflects the sunlight into space. This cools the sea surface between Africa and the Americas in average by 0.15 degrees.
At first glance, the figure is small. But, as shown by calculations, this is enough for cyclones in this part of the world from the West, systematically avoided the Northern half of Africa. Thus, the cold automatically makes the Sahara area without rain. On the contrary, in a warmer climate, it begins to be covered with vegetation.
Over the past quarter century due to global warming, herbaceous plants there were covered with millions of square kilometers, although its role here was played not only by precipitation, but the increase in carbon dioxide in the atmosphere.
It is now clear that by itself, dust from the Sahara could not be the cause of global cooling 5 000 years ago.
Such dust is formed, we need the plants to die in the Sahara because up to this point, their root systems will not allow the winds to freely move the local soil. However, the work shows that the principal mechanism of desertification in this part of the world was the blocking of the sediment transport due to the decrease in sea surface temperature in the Atlantic.
Thus, knowing the dynamics of the climate over the ocean in the area, it is possible to predict the fate of the Saharan region as a whole.
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