orests precede civilization,' it is said, 'deserts follow'. It has been so since humanity first settled down from a nomadic life. More than 3,000 years ago, Gilgamesh - the world's first ever written story - warned against the cutting down of the cedar forests of Mesopotamia. It went unheeded and the region is now desert, with Uruk - the great city where it was written - no more than a bump in the sand. Plato lamented how ancient Greece had been stripped of trees and soil, while the Mayan civilization of Latin America also partly owed its demise to desertification.

Now the same process threatens much of the world. Land degradation affects one third of the Earth's land surface and endangers the health and livelihoods of over a billion people, more than one in every seven people on the planet. Over 100 countries - rich and poor - are affected. So is every continent apart from Antarctica. It is probably the world's most widespread environmental crisis.

For the first time, however, the world is at least recognizing the problem. An international treaty - the United Nations Convention to Combat Desertification - came into force 10 years ago. And 2006 has been designated by the United Nations as the International Year of Deserts and Desertification to try to call attention to the issue. This is also the theme of the worldwide celebrations of this year's World Environment Day.

Sadly, progress in tackling the problem over the last decade has been painfully slow. Perhaps because it mainly affects marginalized and poor peoples - often from ethnic minorities - it has rarely been a top priority of most governments or of the international community. And yet the longer it is ignored, the worse it gets, putting all our futures at risk. It is a tall order to reverse the trend of thousands of years, to turn back the desertifying blight that has both doomed successive civilizations and been their legacy. But it has to be done - and done within the lifetime of our generation. We must seize the challenge.