Governments must do more to fight global warming, spurred by a new U.N. scientific report and damage to nature that is already as frightening as science fiction, U.N. Secretary-General Ban Ki-moon said on Saturday.

This report will be formally presented to the (U.N. Climate Change) Conference in Bali, Ban told delegates from more than 130 nations in Valencia and praised them for agreeing an authoritative guide to the risks of climate change on Friday.

Already, it has set the stage for a real breakthrough -- an agreement to launch negotiations for a comprehensive climate change deal that all nations can embrace, he said.

Ban singled out the United States and China, the world's top two emitters of greenhouse gases, which have no binding goals for curbs, as key countries in the process. He welcomed initiatives by both and urged them to do more.

I look forward to seeing the U.S. and China playing a more constructive role starting from the Bali conference, Ban told a news conference. Both countries can lead in their own way.

Ban said he had just been to see ice shelves breaking up in Antarctica and the melting Torres del Paine glaciers in Chile. He also visited the Amazon rainforest, which he said was being suffocated by global warming.

I come to you humbled after seeing some of the most precious treasures of our planet -- treasures that are being threatened by humanity's own hand, he said.

These scenes are as frightening as a science fiction movie, Ban said. But they are even more terrifying, because they are real.

Delegates at U.N. climate change talks reached agreement on the 26-page document about the risks of warming, blamed mainly on human burning of fossil fuels, after several days of talks.

The document, which summarizes the latest scientific knowledge on the causes and effects of climate change, will be put before environment ministers in Bali, Indonesia, next month -- a meeting likely to agree a two-year strategy to negotiate a successor to the Kyoto Protocol whose first period ends in 2012.

The summary says human activity is causing rising temperatures and that deep cuts in greenhouse gas emissions, mainly from burning fossil fuels, are needed quickly to avert more heat waves, melting glaciers and rising sea levels.

BALI MEETING

Scientists and government officials from the 130-state Intergovernmental Panel on Climate Change (IPCC) have boiled down the findings of three reports of more than 3,000 pages issued this year on the risks of warming.

Delegates from the environmental movement appeared relatively happy the synthesis had not watered down the message from the scientific advisers, as they had feared it might.

The strong message of the IPCC can't be watered down - the science is crystal clear. The hard fact is we have caused climate change, and it's also clear that we hold the solution ... in our hands, said Hans Verolme, Director of environmental group WWF's Global Climate Change Program.

Delegates said the U.S. delegation had been at the centre of some of the fiercest debate this week.

Sources close to the discussions said the U.S. had tried to change or even remove a key section of the report which lists five main reasons for concern about the effects of warming.

This has been a very tough week and we've had to debate and defend everything we wanted but the draft report that we submitted has remained intact and has even had additions made in terms of emphasis and even facts that have come to light, IPCC Chairman Rajendra Pachauri told Reuters.

When you're on strong scientific ground, you don't yield any ground. We have to make sure that scientific truth is not suppressed.

The Kyoto treaty obliges 36 industrial nations to cut emissions by at least 5 percent below 1990 levels by 2008-12. A new deal would aim to involve outsiders led by the United States and China, which have no Kyoto goals.

(Additional reporting by Alister Doyle in Oslo; editing by Tim Pearce)

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