Deserts cover a third of the world’s land surface, they have a powerful role in the planetary climate machine, and they are home to 500 million people. And – as the International Union for the Conservation of Nature has been saying at the world heritage committee meeting in Brasilia, which finished last week – deserts are unique and fragile environments that are home to a remarkable array of plants and animals. The dust whipped up by storms in the Sahara or the arid highlands of Asia absorbs sunlight and darkens the skies, but at the right altitude the same dust also provides surfaces on which water vapour can nucleate as ice to fall as rain. The same dust storms have been linked to outbreaks of respiratory disease in the US and Europe, and to sudden eruptions of plant and animal disease across the distant oceans: one gram of Saharan dust carries a burden of a billion microbes, and some of these are certainly plant and animal pathogens.

But the world heritage meeting also hailed one of the most remarkable discoveries of the last decade: the role of deserts as deliverers of nutrients to the rainier parts of the planet. Around 40m tons of dust is carried by prevailing winds from the Sahara to fertilise the Amazon basin each year. This is a very satisfying finding, since the extraordinary fertility of the Amazon rainforest – one of the richest and most biodiverse places on earth – has been a puzzle. Tropical rains leach nutrients from jungle soils, and the soils of the Amazon forest are notoriously poor, which is why clearance for cattle farming is such a bad idea. Biologists had calculated that the forest needed at least 50m tons of fresh mineral nutrient each year to keep its trees tall and in leaf. In 2006 an international team of researchers established that at least half of this annual mineral supply is quarried from one tiny location in the Sahara, the Bodélé depression in Chad. A combination of fortuitously placed mountain ranges that flank a basin of diatomite sands so focus the winter winds as to scour the depression and lift from it an average of 700,000 tons of dust each day, and air-freight it across the Atlantic.

So for thousands of years, and without any fuss, a tiny part of one of Africa’s poorest countries has annually subsidised the growth economy of one of the world’s most richly endowed. This discovery is yet another insight into the intricate dance performed by earth, air, fire and water in the service of life; and another reminder of the enduring intercontinental interdependence that sustains human civilisation. We should respect the IUCN’s concern for the deserts. Without green things, we could not breathe. Without deserts, there might be no forests.