The summit is expected to discuss a new agreement to curb carbon emissions after the Kyoto Protocol expires in 2012.

  

Ban flew over melting ice fields and witnessed vast chunks of ice the size of six-storey buildings floating off the coast after breaking away from ice shelves.

"All we have seen has been very impressive and beautiful, extraordinarily beautiful," he said.

 

"But at the same time it's disturbing. We have seen ... the melting of glaciers."

 

Andean glaciers

 

Ban is expected to continue his South American tour by visiting Torres Del Paine, Chile's national park, where the Andean glaciers are suffering from global warming.

  

He will then visit Brazil, a leading force in developing bio-fuels from crops as an alternative to fossil fuels.

 

Fears about climate change have fuelled a boom in bio-fuels.

   

Despite the controversy over diverting food crops into fuel production, Ban has said alternative energy sources are vital to addressing climate change.

 

Thinning sheet   

 

Temperatures in Antarctica are the highest they have ever been in about 1,800 years.       

 

Antarctica's ice sheets are nearly 2.5km thick on average - five times the height of the Taipei 101 tower, the world's tallest building.

 

But scientists say they are already showing signs of the impact of climate change.

   

Satellite images show the West Antarctic ice sheet is thinning and may even collapse in the future, causing sea levels to rise.

   

Antarctica - a continent of only 80,000 temporary residents - is 25 per cent bigger than Europe and its ice sheets hold some 90 per cent of the fresh water on the Earth's surface.