Some experts now argue that some deserts could get greener. Ayisha Yahya explores the arguments in Mali, Egypt and Namibia.
In the final part of this series, Ayisha meets scientists in Egypt experimenting with high-tech techniques to make the desert bloom.
The Egyptian government is keen to encourage people to move to the desert.
They want to press ahead with a controversial plan to reclaim a further 3.4 million acres of desert over the next 10 years.
Ayisha Yahaya asks, is this plan practical or sustainable or might it ultimately backfire?