By Barbara Plett
BBC News, northern Norway
Mr Ban travelled north to the Arctic on a Norwegian coast guard vessel
UN Secretary-General Ban Ki-moon is visiting the Arctic Circle in Norway to draw attention to the need for action at climate change talks in December.
Mr Ban said it was "absolutely crucial" that world leaders took united action.
In December, leaders must agree on a successor to the Kyoto Protocol for cutting carbon emissions, which are believed to cause global warming.
Scientists warn that the results of climate change could be catastrophic if greenhouse gas production is unchecked.
Mr Ban began his trip to the Arctic Circle by saying he wanted to see for himself the melting polar ice cap.
But a planned visit to the North Pole was later delayed because of bad weather, and it is not yet clear when he will be able to travel there.
After boarding a Norwegian coast guard vessel, he told journalists he was trying to inject some urgency into current negotiations for a global treaty to cut carbon emissions.
Mr Ban says climate change could cause the polar ice caps to melt
Scientists warn that greenhouse gasses have caused Arctic ice to melt even faster than predicted, something the UN chief said was deeply disturbing.
"If this trend is not stopped, we may have a virtually ice-free Arctic within 30 years," said Mr Ban.
"This is quite alarming, therefore it is absolutely crucial that world leaders are united to take urgent action. This is my commitment, that is why I'm going to the Arctic."
The treaty is set to be finalised in Copenhagen by the end of the year, but negotiations have been plagued by disputes over which countries should make emissions cuts and by how much.
Mr Ban said he was strongly encouraged by the campaign promises of Japan's newly-elected leader, Yukio Hatoyama, who pledged a 25% emissions reduction by 2020.
The secretary general said he hoped other developed nations would follow suit.
Earlier he defended himself against charges that he was a weak leader who lacked charisma, a criticism leaked from an internal memo drawn up by a senior Norwegian diplomat.
Mr Ban has been a strong advocate of action to stop climate change, and is convening his own summit on 22 September to build political momentum for the Copenhagen meeting.