How can a part of the world transform from a green area into a desert? It happened to the Sahara and scientists think this was due to a change in the tilt of the earth. Changes in the Earth's tilt happen from time to time and they change the weather. A change in our orbit could have done the same thing, and scientists say the earth's orbit continues to change and will continue to do so in the future.
Researchers all agree that this area changed into the world's biggest desert, but the question is: Was the path to change gradual or fast and HOW and WHY did it happen? NASA's Gavin Schmidt thinks the change happened quickly, 8,000 years ago, when the Earth's orbit changed from around 24.1 degrees to the 23.5 degrees, where it remains today. The Daily Galaxy quotes him as saying, "The end of the 'Green Sahara' came about quite suddenly around 5,500 years ago. Thus, a very slow change in the orbit (led) to an abrupt collapse in that ecosystem. The Earth had its closest approach to the Sun in the northern hemisphere (with) summer in August. Today, that closest approach is in January. So, summertime in the north was warmer back then than it is now."
Pierre Francus is an advocate of slow change. The Daily Galaxy quotes him as saying, "The findings of this study are that the sedimentological and geochemical properties of the lake sediments confirm that the Sahara has been drying slowly from six thousand years ago to reach the present day conditions around 1,100 years ago. The models that are used to predict future climate need to be tested, and using information from the past is one way to achieve this goal."