By Gideon Long
BBC News, Chile
United Nations Secretary General Ban Ki-moon has described his alarm at the pace of climate change after wrapping up a two-day fact-finding trip to southern Chile.
The UN chief saw first hand scientific evidence of global warming
Mr Ban, who has vowed to make the fight against global warming a key issue during his tenure at the UN, went to Antarctica on Friday where he heard from scientists how rising temperatures have caused huge ice shelves to collapse into the sea.
He was the first head of the UN ever to visit the frozen continent.
On Saturday the secretary general visited the majestic mountains of the Torres del Paine national park, one of Chile's top tourist attractions.
He flew over the Grey glacier, the facade of which is covered in cracks, which experts blame on changes in the weather.
Mr Ban is gathering information to take to a major UN conference on climate change next month on the Indonesian island of Bali.
Among the scientists who briefed him was Gino Casassa, one of Chile's leading experts on climate change and a member of the UN's Intergovernmental Panel on Climate Change (IPCC), which won this year's Nobel Peace Prize for its work on the issue.
"The Antarctic peninsula is one of the three [climate change] hotspots on earth and the temperature increase here over the last 50 years has been up to 10 times the global average," Mr Casassa said, as he stood in thick snow at one of two permanent Chilean bases on the continent.
"These are really astonishing changes, and nobody thought they would happen so fast.
"The heat is migrating south, warming up the ice and melting it. And as it does the ice just collapses into the ocean.
"We are having to reshape the whole glacialogical theory thanks to what we've been witnessing on this peninsula."
Speaking to reporters who accompanied him to Antarctica, the UN secretary general said the world had to do more to safeguard the future of the planet.
"I'm not here to frighten you, I'm not scaremongering," he said. "But the world is changing, the glaciers are melting ... the change is now progressing much faster than I had thought. It's alarming."
During his trip to Antarctica, Mr Ban dropped in on his compatriots at South Korea's King Sejong research station, also on the Antarctic peninsula.
Mr Ban will attend a major UN climate summit next month in Bali
There, scientists have monitored the impact of global warming on a glacier which has retreated over 1km (0.62 miles) in the past half century.
"Very, very serious global warming is taking place," said the head of the base, Sang Hoon Lee.
For years, many scientists cast doubt on the existence of global warming but these days the sceptics are dwindling in number.
"Even when I was studying for my PhD I didn't think there was enough evidence," Mr Casassa said. "It was less than 10 years ago that I was converted."
From Chile, Mr Ban flew to Brazil, where he is due to visit an ethanol plant and see how the burning of fossil fuels has affected the Amazon rainforest.
When he travels to Bali next month his main priority will be to kick-start negotiations aimed at agreeing a follow-up to the 1997 Kyoto Protocol on cutting greenhouse emissions.