Its dunes are the dried-out remains of the bed of the vast Lake Megachad which covered central Sahara until its abrupt

Its dunes are the dried-out remains of the bed of the vast Lake Megachad, which covered central Sahara until its abrupt demise 5,500 years ago.Most of the dunes are not made of sand or broken rock. They are the remains of trillions of diatomites, microscopic freshwater creatures that once lived in the lake These fragments are light enough to blow freely in the wind. Saharan dust storms carry huge amounts of minerals and organic matter that enrich soils widely in the Americas Bodele dust seems especially valuable. It seems that dust in the air interrupts the updraughts that fuel the storms. Equally surprisingly, desert bacteria caught up in the winds are being blamed for bringing new diseases to Caribbean coral reefs and triggering asthma among Caribbean children And there is a third important link.

According to hurricane forecasters in Florida, during dry, dusty years in the Sahara there are fewer hurricanes on the other side of the Atlantic. The amount of dust crossing the Atlantic grew five-fold between the wet 1960s and the dry 1980s.The Sahara dust has a series of unexpected effects on the Americas. But much of it is carried west across the desert wastes of Niger, Mali and Mauritania before heading out over the Atlantic. The red dust clouds can grow three kilometres high as they approach America.

They cause spectacular sunrises over Miami, before falling in the rains of the Caribbean and the Amazon. And there have been a lot of good sunrises in recent decades. According to Richard Washington of Oxford University, two-fifths of the dust in the atmosphere comes from the Sahara, and of that half comes from Bodele.Some of this dust stays local. It is littered with unexploded bombs and land mines left behind during Libya’s invasion during the 1980s And it is by some way the dustiest place on Earth. Satellite images show year-round dust storms raging across Bodele and entering the atmospheric circulation. Their fates may be intertwined in a rather unexpected way – and one that could have important consequences in the near future.The key to the symbiosis lies in a region called Bodele in northern Chad Few people go here.

Near the equator, the two are less than half as far apart as London and New York.Many believe the two areas have a surprising symbiosis. The Amazon is one of the wettest places on Earth, and its most biologically diverse But these two opposites are not so far apart For one thing, the physical gap is surprisingly small. On one side is the Amazon rainforest; on the other the Sahara The Sahara is rainless and largely empty of vegetation. Perhaps the greatest likelihood is that in many places, from the Sahara to the American West and Arabia, there will be more and longer droughts, interspersed with brief but devastating floods.SEE-SAW ACROSS THE OCEAN – how the Sahara desert greens the AmazonTwo of the world’s largest and most fragile ecosystems face each other across the Atlantic. It is not obvious which force will win, and where.Will the Sahara desert expand and intensify as the drought theorists argue? Or will North Africa be reclaimed by a revived African monsoon? Megadrought or Garden of Eden? Nobody can answer that question yet. But the rain-bearing winds will often by confronted by intensifying arid zones of descending air in the continental interiors.