The world's deserts are under threat as never before, with climate change making lack of water an even bigger problem for the planet's last great wildernesses, a UN report released Monday said. The first comprehensive look at the world's parched areas, "Global Deserts Outlook" said these regions, their wildlife and, most of all, their scarce water supplies are facing dramatic change. "Deserts are the last great wildernesses and the Cinderellas of the conservation world - out of sight, out of mind," said Nick Nuttall, a spokesman for the United Nations Environment Program. "Everybody cares about the mountains. Everybody is worried about the oceans. ... But nobody has really thought about the deserts before. They need help." The report depicts deserts as rich cultural and biological worlds far more complex than the common image of them as mere seas of sand. Desert areas make up one quarter of the Earth's surface, or 33.7 million square kilometers (13 million square miles), and are home to some 500 million people, more than previously thought.