The Rongbuk glacier, the biggest glacier on Mount Everest's northern slopes. The photo above was taken in 1968 and the one below was taken this year (2007).
Photo: Chinese Academy of Sciences and Greenpeace

These two photographs - taken 40 years apart - show how one of the world's most spectacular ice formations, the field of ice towers ("serac forest") around Mount Everest, is shrinking. Environmental group Greenpeace, which released the photographs today, say this is global warming in action.

The photographs are of the Qinghai-Tibet plateau, which is called the world's "third pole" because it contains the biggest fields of ice outside of the Arctic and Antarctic. Its glaciers are the source of Asia's biggest rivers - Yangtze, Yellow, Indus and Ganges.

The melting of this glacier is also significant because the UN's Intergovernmental Panel on Climate Change reported last month that if current trends continue, 80 per cent of the Himalayan glaciers, the water source for a sixth of the world's population, could disappear in 30 years if the current rate of emissions is not reduced. Other reports have suggested that the impact would be lower, at about 30 per cent.

The original picture from 1968 was taken by the Chinese Academy of Sciences. Greenpeace has made three expeditions to the same area in the past two years.

The Greenpeace campaigners were unable to reach the same spot where they think the 1968 picture was taken because a smaller glacier that was there four decades ago has disappeared, making it impassable. The season in which the 1968 photograph was taken is also unknown, though there are really only two periods when the area is habitable by humans, which is April to May (spring) and September to October (autumn).