Satellite pictures, often taken three decades apart, showed expanding cities, pollution, deforestation and climate change were damaging the African environment despite glimmers of improvement in some areas.

"Africa is losing more than 4 million hectares (9.9 million acres) of forest every year -- twice the world's average deforestation rate," according to a statement by the UN Environment Programme (UNEP) about the 400-page atlas, prepared for a meeting of African environment ministers in Johannesburg, South Africa.

Photographs showed recent scars in forests in countries including the Democratic Republic of Congo, Malawi, Nigeria and Rwanda. It said forest loss was a major concern in 35 countries in Africa.

Malawi mostly loses its forest due to unnecessary cutting of trees which people use for making charcoal.

And it showed that environmental change extended beyond the well-known shrinking of the snows on Mount Kilimanjaro in Tanzania, Africa's highest peak at 5,895 metres (19,340 ft), or the drying up of Lake Chad.

Four million hectares is roughly the size of Switzerland or slightly bigger than the US state of Maryland.

On the Ugandan border with Democratic Republic of Congo, for instance, glaciers on the Rwenzori Mountains where the highest peak is 5,109 metres shrank by half between 1987 and 2003, it said.

Trees and shrubs had been cut from the Jebel Marra foothills in Sudan, partly because of an influx of refugees from the conflict in Darfur.

"The Atlas ... clearly demonstrates the vulnerability of people in the region to forces often outside their control, including the shrinking of glaciers in Uganda and Tanzania and impacts on water supplies linked with climate change," UNEP head Achim Steiner said in a statement.

A Reuters report Tuesday said the atlas said 300 million people faced water scarcity and that areas in sub-Saharan Africa experiencing shortages were expected to increase by almost a third by 2050.

"Climate change is emerging as a driving force behind many of these problems," it said.

Almost 200 governments have agreed to work out a new U.N. treaty by the end of 2009 to slow climate change, blamed mainly on emissions of greenhouse gases from burning fossil fuels.

But the atlas said there were signs of hope.

"There are many places across Africa where people have taken action -- where there are more trees than 30 years ago, where wetlands have sprung back and where land degradation has been countered," Steiner said.

Among examples, the report showed that action to prevent over-grazing had helped a national park in south-eastern Tunisia. A project to expand wetlands in Mauritania was also helping to control flooding and improve livelihoods.