Why does the sahara dry out

Even then, pirates were already a danger, deMenocal explains in the video above. By fax, the ship received updates of known pirate attacks, some near sites they had planned to core. But they got their core and eventually docked safely in Egypt. Notify of. The research team deconstructed this story from leaf waxes, whereby they measured the isotopes of deuterium within the plants to record a proxy for rainfall in the area.

Plants record the amount of rainfall they experience in their cells, altering the isotope ratios of various elements depending on regional climate conditions. This is a common way geologists reconstruct climatic conditions of the past.

This means slight variations in average temperature of the northern high latitudes could have a "light switch" effect turning on and off precipitation in northern Africa. Considering the recent warming of the planet, nowhere more so than high latitudes, it will be interesting to see if northern Africa at some point flips to a more tropical and humid environment.

While historical data suggests this is likely if warming continues, the process could take hundreds of years and it's unclear how fast that tipping point is. While this may seem like a net positive effect of a warming planet, it's important to realize that there is a finite amount of rainfall around the world. If one region becomes significantly wetter, one would expect another region to become significantly drier.

This could mean the emergence of mass migrations from areas that increasingly have less rainfall to areas that increasingly have more rainfall.

The samples contained layers of ancient sediment built up over millions of years. Each layer could contain traces of Saharan dust as well as the remains of life forms, MIT News reported. This information was used to estimate over what time period the dust had built up. This led to the overall finding that the Saharan changes from wet to dry climates happened every 20, years.

Hai Do was the editor. We want to hear from you. Write to us in the Comments section, and visit our Facebook page. Load more comments. Search Search. Audio menu. Tierney suggests researchers could use mathematical models that compare the impact hunter-gatherers would have on the environment versus that of pastoralists herding animals.

For such models it would be necessary to have some idea of how many people lived in the Sahara at the time, but Tierney is sure there were more people in the region than there are today, excepting coastal urban areas. Wright sees an even broader message in this type of study. Some of these can be good for us, but some have really threatened the long-term sustainability of the Earth. Lorraine Boissoneault is a contributing writer to SmithsonianMag.

She has previously written for The Atlantic, Salon, Nautilus and others. One of the world's most iconic deserts was once lush and green.