Nearly six hundred warm blooded, art loving environmentalists pose nude on a shrinking Swiss glacier for American photographer Spencer Tunick. Hundreds of people posed naked on Switzerland's shrinking Aletsch glacier on Saturday for U.S. photographer Spencer Tunick as part of a Greenpeace campaign to raise awareness of global warming. Tunick directed nearly 600 people from all over Europe and photographed them on the glacier, which is the largest in the Alps, at more than 2,400 metres altitude. Receding glaciers are important indicators of climate changes, and their decline is said by experts to have accelerated at double speed in the past two decades. Environmental group Greenpeace, which organised the shoot, said the aim was to establish a symbolic relationship between the vulnerability of the melting glacier and the human body. "This is a human art work that has to do mostly with a reaction to what is happening, and hopefully a proactive stance against what could happen," Spencer Tunick said. The Aletsch glacier is 23 kilometres (75,463 ft - 14.29 miles) long, and covers a surface of 86 square kilometres (53 square miles), which makes it the longest stream of ice in Europe. It was designated a UNESCO world heritage site in 2001, in recognition of its unique position in the European Alps and of the wide diversity of ecosystems it features, including clues from the past from the retreat of glaciers resulting from climate change. Retreating by up to 50 metres (164 ft) a year, the Great Aletsch glacier has been dramatically affected by decline in recent years. Tunick said because of global warming and climate change there would be no drinking water from the Swiss glaciers in about fifty years. In forty years most of the Aletsch glacier would be gone. Although the receding of a glacier is not unusual, the speed of retreat observed in the past decades gives cause for concern, showing the strong mark of climate change. Here, the much-cited climate change is leaving its mark in quite significant proportions. There are more than 4,500 glaciers in the European Alps, and scientists estimate they have lost over 50% of their volumes since the 19th century.