 Antarctic glaciers are melting, Ban Ki-moon warned |
Mr Ban - the first UN chief to visit the continent - wanted to see for himself the effects of climate change on the world's largest wilderness.
After flying over melting glaciers, he told reporters that what he had seen had been both "extraordinarily beautiful" and "disturbing".
Mr Ban is preparing to host a climate conference in Indonesia in December.
The secretary general flew to Antarctica from southern Chile, and was briefed by experts about the impact of global warming on the frozen continent.
Antarctica is home to about 90% of the world's ice, but scientists say some parts are melting fast.
 |  "This is an emergency and for emergency situations we need emergency action" Ban Ki-moon |
Over the next century global warming could speed up the melting of the polar ice caps, causing major flooding of lowlands and changes in crop production, experts have warned.
Wrapped in thick clothing, Mr Ban was taken to see a glacier and visited a research station set up by South Korea, his home country.
He urged the world to do more to safeguard the future of the planet.
"This is an emergency and for emergency situations we need emergency action," he said.
Mr Ban has vowed to make climate change a priority.
The December conference in Bali, Indonesia, is aimed at launching talks on a deal to replace the Kyoto accord - which expires in 2012
