Series of before and after panoramas of Imja glacier taken five decades apart highlights dramatic reduction of Himalayan ice

When Fritz Müller and Erwin Schneider battled ice storms, altitude sickness and snow blindness in the 1950s to map, measure and photograph the Imja glacier in the Himalayas, they could never have foreseen that the gigantic tongue of millennia-old glacial ice would be reduced to a lake within 50 years.

But half a century later, American mountain geographer Alton Byers returned to the precise locations of the original pictures and replicated 40 panoramas taken by explorers Müller and Schneider. Placed together, the juxtaposed images are not only visually stunning but also of significant scientific value.

The photos have now been united for the first time in an exhibition organised by the International Centre for Integrated Mountain Development (Icimod) and are printed here for the first time in Britain.

The Himalaya – Changing Landscapes exhibition opened in Bonn this week as delegates gathered ifor the next round of UN talks aimed at delivering a global deal on tackling global warming. The series of pictures tell a story not only about the dramatic reductions in glacial ice in the Himalayas, but also the effects of climate change on the people who live there.

"Only five decades have passed between the old and the new photographs and the changes are dramatic," says Byers. "Many small glaciers at low altitudes have disappeared entirely and many larger ones have lost around half of their volume. Some have formed huge glacial lakes at the foot of the glacier, threatening downstream communities in case of an outburst."

His scientific results were published in the Himalayan Journal of Sciences and he is now in the Cordillera Blanca mountains in Peru where he will replicate Schneider's 1930 photos of glaciers.

"Much remains uncertain about the melting of glaciers and future water supplies," he said. "But what is certain is that by promoting the conservation and restoration of mountain watersheds we can counter many of the impacts of warming trends, by creating cooler environments, saving biodiversity and protecting water supplies."

The effects of climate change are dramatically illustrated at the world's "third pole", so-called because the mountain range locks away the highest volume of frozen water after the north and south poles.

The 1956 photograph of the Imja glacier, then one of the largest glaciers at an altitude of around 5,000m, shows a layer of thick ice with small meltwater ponds. But by the time Byers took his shot in 2007, much of the glacier had melted into a vast but stunning blue lake. Today, the Imja glacier, which is just 6km from Everest, continues to recede at a rate of 74m a year - the fastest rate of all the Himayalan glaciers.

Nepal's average temperature has increased by 1.5C since 1975 . A major UN Environment Programme report last year warned that at current rates of global warming, the Himalayan glaciers could shrink from 500,000 square kilometres to 100,000 square kilometres by the 2030s - a prediction supported by the rate of retreat seen in Byers' pictures.

Imja is one of 27 glacial lakes in Nepal classified as potentially dangerous. If the moraines which dam the lake are breached, thousands of lives in the most densely populated Sherpa valley in Nepal are at risk from flooding and landslides.

Himalayan glaciers also feed into major Asian river systems including the Ganges, Indus, Mekong and Yangtze. If glacial meltwaters turn to a trickle, widespread droughts will threaten the 1.3 billion people that depend on water flowing in those rivers .

Andreas Schild, the director general of Icimod, said the photographs reveal just "the tip of the iceberg".

"Scientific evidence shows that the effects of globalisation and climate change are being felt in even the most remote Himalayan environments," he said. "While climate change is mostly caused by the highly industrialised parts of the world, the effects are taking their toll in the sensitive mountain areas. The signs are visible, but the in-depth knowledge and data from the Himalayan region is largely missing. What happens in this remote mountain region is a serious concern for the whole world."