The once-green Sahara turned to desert over thousands of years rather than in an abrupt shift as once thought, according to a study that may help understanding of future climate changes.
Encroaching dunes threaten one of the few remaining lakes at Ounianga, northeast Chad.
And there are now signs of a tiny shift back towards greener conditions in parts of the Sahara, apparently because of global warming, says the lead author of the report published today in the journal Science.
The Sahara's largest lake, Lake Yoa in northeast Chad, is wholly sustained by fossil groundwater dating from the humid past. Its bottom deposits provide the only continuous high-resolution climate archive of the world's major desert
The study of ancient pollen, spores and aquatic organisms in sediments
shows the region gradually shifted from savannah 6000 years ago towards the arid conditions that took over about 2700 years ago.
of water a year by evaporation
But groundwater replaces it
clipped from: www.abc.net.au 
