Believe it or not the Sahara Desert was once a savannah. It was covered with rivers and trees. And it was home to many animal species including the elephant, lion and giraffe. So how did the green land turn brown? Climate change. But it didn't happen overnight and, unlike global warming, it isn't attributable to man. German scientists think that the desertification of the Sahara was set into motion by a tiny shift in Earth's orbit roughly 9,000 years ago. This shift changed the point of Earth's orbit closest to the sun and caused the weather to change. It increased the number of hot sunny months and reduced the amount of rain in North Africa.