Next weekend, he is to attend the unveiling of the fourth Intergovernmental Panel on Climate Change (IPCC) report in Valencia, Spain.

The document is seen as a landmark reference paper for governments trying to tackle global warming -- and a key text that will be read ahead of a Bali conference in December on the issue that Ban will host.

"I hope that by this time the world leaders and the international community have fully understood the urgency and importance of this accelerating global warming phenomenon," he told AFP Tuesday on a flight back from Brazil's Amazon basin.

"Now I'm going to continue with my consultations and my role as a messenger of early warning on climate change until I go to Bali," he said.

"By the time we meet in Bali, I hope we will agree to launch on official negotiations" aimed at coming up with an international accord to succeed the Kyoto treaty, which expires in 2012.

Negotiators at the Valencia talks said there was wrangling over the final 2,500-page report, which is intended to be a neutral guide for decision-makers.

One negotiator described the talks as "difficult," with sharp exchanges over what the document should include.

The UN secretary general was not to get involved in that haggling.

Upon arrival in Madrid Wednesday he was to hold a meeting with Spanish Prime Minister Jose Luis Rodriguez Zapatero.

He was then to jet off to Tunisia to attend an international counter-terrorism conference, followed by a hastily-organized flight to Lebanon, before returning to Spain to attend the Valencia meeting.

The UN chief has declared tackling climate change one of his top priorities.

He said Tuesday, during a visit to the Amazon jungle, that he was "returning with a sense of great achievement" from what he had learned throughout his trip.

During his tour, he took in Argentina, Chile and the Antarctic before visiting Brazil for three days.

He met Brazilian President Luiz Inacio Lula da Silva on Monday and commended him on his ecological policies.

During his jungle visit, he also repeated to Brazilian officials and indigenous representatives: "I make my firm commitment that the United Nations will work with you and stand by you."

Brazilian Environment Minister Marina Silva, accompanying Ban and his wife up the Guama River in the Amazon basin to Combu Island, near Belem, said "the presence of the UN secretary general is a strong gesture" for Brazil's efforts to preserve the Amazon rainforest.

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