Climate change, high water demand and tourism are putting unprecedented pressures on the world's desert ecosystems, according to a report from the UN's Environment Programme.

At the same time, a Christian Aid report claims, climate change is also threatening development goals for billions of the world's poorest people - risking the possibility that recent gains in reducing poverty will be thrown into reverse.

The UN's Global Deserts Outlook, described as the first comprehensive look at the earth's driest regions, throws new light on the world's arid areas, underlining their potential as well as the problems. "Far from being barren wastelands, deserts emerge as biologically, economically and culturally dynamic while being increasingly subject to the impacts and pressures of the modern world," said Shafqat Kakakhel, from UNEP. "They also emerge as places of new economic and livelihood possibilities, underlining yet again that the environment is not a luxury but a key element in the fight against poverty and the delivery of internationally-agreed development goals."

Global deserts occupy almost one-quarter of the Earth's land surface - some 13 million square miles - and are inhabited by over 500 million people. But for the majority, who live at desert margins, the pressures threatening ecosystems are greatest. Here, population growth and inefficient water use threaten to move some countries - including Chad, Iraq, Niger and Syria - into water stress, or even water scarcity.

The Climate of Poverty: facts, fears and hope, a new report from Christian Aid, suggests that by the end of the century 182 million people in sub-Saharan Africa could die of disease directly attributable to climate change. Millions more, it argues, face devastation from climate-induced floods, famine, drought and conflict.

While the report calls on the UK government to lead rich countries in taking action to curb global warming, it also proposes a revolution in development thinking that could see poor regions using renewable energy to power a new, and clean, era of prosperity. For example, a switch by sub-Saharan Africa away from a model of development based on fossil fuels to one using energy sources like solar, wind and water would not only be better for the environment, but could also provide jobs, better health and new opportunities for learning. The report claims that every household in Africa could change to clean, renewable energy for less money than it would take to pay the region's oil bill for the next decade. And proposes that developing technology could transform the world's most impoverished continent into a net exporter of clean energy.

"This report exposes clearly and starkly the devastating impact that human induced climate change will have on many of the world's poorest people," said Sir John Houghton, former co-chair of the scientific assessment working group of the Intergovernmental Panel on Climate Change. "That realisation exposes an inescapable moral imperative for those of us in the developed world who have benefited so much from cheap energy from fossil fuels. We need to respond with urgent and determined action."

Christian Aid wants the UK government to: institute a strict "carbon budget" which will reduce emissions by two thirds of 1990 levels by 2050; lead rich countries in offering financial support to developing countries in compensation for damage inflicted on the environment and help fund programmes to provide renewable energy to poor communities.