Global warming could double the size of the Kalahari Desert in southern Africa, scientists say.

It is already one of the largest deserts in the world, but less precipitation and stronger winds could spread it over the next century.

The Kalahari stretches as far as South Africa, Botswana and Namibia and is home to millions of people.

But experts warn that it will be difficult for them to survive if the desert expands because there will be less food for their livestock.

Wind speed

The Kalahari is already four times the size of Britain, making it one of the largest deserts in the world.

Experts from the University of Oxford have been studying the desert for 20 years. They predict that climate change will cause wind speeds to increase in the region.

Dunes

For now, the sand that makes up the desert remains pretty much still, but if the wind speed increases to 15 miles per hour, it will disrupt enough grain to move entire dunes.

This in turn will spread the desert over the surrounding farmland and cover any plant life growing at the tip of the dunes.

It is predicted that the poorest people living in the desert will be hit hardest and many of them will have to move to survive.