The deserts of the world are threatened by a combination of human exploitation and climate change that could, within decades, wipe out many unique habitats and rare species, an authoritative study has found.
While climate change is causing many semi-dry regions of the world to become increasingly arid, it is making life more difficult for true deserts that have been in existence for thousands of years.
Deserts account for up to 25 per cent of the Earth's land surface, are home to half a billion people and account for 12 per cent of the biodiversity "hotspots" - the richest areas in terms of rare animals and plants. Yet warmer temperatures and less predicable rainfall caused by climate change threatens to upset the delicate balance of desert life which has been honed by thousands of years of relative climatic stability.
Meanwhile, the human exploitation of desert regions - resulting in the drainage of underground aquifers and soil poisoning through salinisation - is accelerating the rate at which deserts are drying out to the point of being killed off.
Desert margins are particularly vulnerable and it is there that human settlements are most at risk of desertification, according the report by the United Nations Environment Programme. "True deserts are not the final stage of a process of desertification," says the report, Global Deserts Outlook, published today.
"They are unique, highly adapted natural ecosystems, both providing life-supporting services on the planet and supporting human populations in much the same ways as in other ecosystems," the report says.
Andrew Warren, a professor of geography at University College London and one of the report's lead authors, said that over the course of his 45-year career he has witnessed the growing threat to deserts.
"What alarms me now is that they are threatened as never before, by climate change, by over-exploitation of groundwater, salinisation and the extinction of wildlife," Professor Warren said. Desert animals at risk include the gazelle, the oryx, the addax, the Arabian tahr, the Barbary sheep and the Asian houbara bustard.
"We risk losing not only astounding landscapes and ancient cultures, but also some amazing wild species, which, may hold some keys to our survival," he said.
"Many have unique adaptations and genetic make-up which may contribute to new crops and livestock capable of coping with a rapidly warming world."
The UNEP investigation found that climate change over the past 25 years has caused temperatures to rise faster than the global average in nine out of 12 major deserts studied. The study found that the projected temperature increases over the next 75 to 100 years range from 1C to 7C.
Although a few deserts may experience more frequent pulses of heavy rainfall as a result of higher temperatures, many more are likely to become far more arid than they are today. Deserts fed by glacial meltwater - such as the Atacama and Monte Deserts in South America - will suffer most when their glaciers melt beyond a point that will cause rivers to run dry.
"Nearly half of the bird, mammal and butterfly species in the Chihuahua Desert [of south west America and Mexico] are expected to be replaced by other species by 2055," says the report.