Scientists welcomed Ban Ki Moon to Antarctica with a glass of Johnny Walker Black Label served “on the rocks” with 40,000-year-old polar ice. But the researchers delivered an alarming message to the UN Secretary-General about a potential environmental catastrophe that could raise sea levels by six metres if an ice sheet covering a fifth of the continent crumbles.

The polar experts, studying the effects of global warming on the icy continent that is devoted to science, fear a repeat of the 2002 collapse of the Larsen B ice shelf. The 12,000-year-old shelf was 220 metres (720ft) thick and almost the size of Yorkshire.

“I was told by scientists that the entire Western Antarctica is now floating. That is a fifth of the continent. If it broke up, sea levels may rise as much as six metres,” Mr Ban said after being briefed at the Chilean, Uruguayan and South Korean bases during a day trip to King George Island, at the tip of the Antarctic Peninsula.

For Mr Ban, a media-shy former South Korean Foreign Minister, to travel to Antarctica was a dramatic gesture aimed at highlighting his personal concern over global warming. Accompanying the UN chief was his wife, Yoo Soon Taek. The meticulously dressed couple had to don padded polar trousers and anoraks in the hold of a Chilean military transport aircraft during the 2½hour flight from Punta Arenas, southern Chile.

Mr Ban skipped a three-course lunch that the Chilean Air Force had prepared so that he could land by ski-plane on the retreating Collins glacier. “What we have seen is very impressive and beautiful,” he said. “But at the same time it can be disturbing too.”

Eduardo Frei Montalva Air Force Base, a year-round settlement of corrugated-iron cabins belonging to Chile, lies in one of the world’s worst “hot spots” – temperatures have been rising 0.5C (0.9F) a decade since the 1940s. The base is still coated in thick snow and the bay still frozen because of an unusually harsh Antarctic winter. The temperature for the UN chief’s visit was a tolerable minus 4C (25F). The arrival of the austral summer would normally have turned the ground to mud by this time of year. Yet scientists say that what matters for the polar ice is not how cold it gets in winter but how hot it gets in summer. And they are alarmed at the extremes of temperature.

Sang Hoon Lee, the chief of the South Korean research station, said: “The most evident change is the retreat of the glacier in front of the Korean station, which has been more than one kilometre in the past 50 years. That means very, very serious global warming is taking place.”

Gino Casassa, a Chilean member of the Nobel Peace Prize-winning Intergovernmental Panel on Climate Change, said: “The climate change here in the past ten years has been up to ten times the global average.”

The change was predicted by John Mercer, a glaciologist, he said. The late Dr Mercer, who worked at Ohio State University, theorised that the collapse of ice shelves along the Antarctic Peninsula could be a harbinger of the disintegration of the much larger West Antarctic Ice Sheet, which would raise global sea levels by six metres over the course of a century.

His warning was first published in the journal of the International Association of Scientific Hydrology in 1968, but attracted little attention until it was published in Nature magazine a decade later. Now it has the UN Secretary-General’s attention as he prepares for a UN climate change conference in Bali next month aimed at trying to agree limits on “greenhouse gas” emissions once the restrictions specified by the Kyoto Protocol expire in 2012. Before that Mr Ban will go to Valencia, in Spain, for the launch on Saturday of a fourth and final report by the Intergovernmental Panel on Climate Change, summing up the findings of the panel’s 2,500 scientists.

The panel’s last major report, in 2001, predicted that the Antarctic ice cap would grow in size in the 21st century before shrinking and adding “several metres” to global sea level “over the next 1,000 years” – a finding that the panel is now expected to reassess.

“This is an emergency. For an emergency situation we need an emergency act,” Mr Ban said before his flight back to Chile. “We have resources. We have financing. Only lacking is political will.”

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