(CNN) -- Climate change is "severe and so sweeping that only urgent, global action" can head it off, a United Nations scientific panel said in a report on global warming issued Saturday.
Exposed mud banks at a reservoir in Spain, November 2007.
The report produced by the Nobel prize-winning panel warns of the devastating impact for developing countries and the threat of species extinction posed by the climate crisis.
U.N. Secretary-General Ban Ki-moon, presenting the Intergovernmental Panel on Climate Change report in Valencia, Spain, warned that some of the effects of rising levels of greenhouse gases may already be irreversible.
The U.N. head said the situation was already "so severe and so sweeping that only urgent, global action" could head off the crisis.
The report warns that in spite of the protocols adopted by many Western countries after Kyoto, greenhouse gas emissions will continue to rise by between 25 and 90 per cent by 2030.
The Kyoto treaty was a global effort to reduce emissions of greenhouse gases. The United States is one of only a few nations not to have signed the protocol, which expires in 2012.
The report also predicts a rise in global warming of around 0.2 degrees Celsius per decade.
Scientists say up to an 85 percent cut in carbon dioxide emissions is needed to head off potential catastrophic changes that could lead to more floods and famine.
Ban Ki-moon told the panel he was hopeful that the report's findings could help bring about "a real breakthrough" in climate change negotiations in Bali, Indonesia, next month.
The climate change panel was delivering its fourth and final report on the science of climate change and the impact of human-produced greenhouse gases at a conference in Valencia.
The Bali talks will set the groundwork for the successor to the Kyoto treaty.
They will also guide global climate policy for at least the next decade, and dictate the types of long-term investment decisions made by big industries and utilities.
Written by more than 2,500 top government-appointed scientists, Saturday's report contains a summary for policymakers attending the Bali talks, outlining the scientific evidence for global warming and ways to deal with it.
However, panel member Achim Steiner, executive director of United Nations environment program, said the report was also meant to serve as a "civilian's guide" to dealing with climate change. He said he hoped individuals could use the information contained in the report to take practical steps to curbing gas emissions.
The U.N. panel -- the recent recipient of the Nobel Peace Prize with former U.S. Vice President Al Gore -- was asked if goals of reducing emissions could be achieved without the contribution of China and especially the United States, which was one of only a few countries that did not sign up to the Kyoto treaty.
Ban Ki-moon said he had "high expectations" that both countries would play a "constructive role" at the upcoming talks.
"Both countries I think can and should lead each in its own way," he said.
The disagreement over how the cuts in carbon dioxide emissions should be managed may well stall the Bali talks.
Some countries are thought to be in favor of mandatory caps on emissions, which could hit the industrial output of major carbon dioxide producers such as the United States.
Mandatory caps are also unlikely to be supported by developing countries, who fear they could be a barrier to growth.
Opponents of the caps -- thought to include the Bush administration -- favor voluntary restrictions and suggest postponing mandatory caps until the richer world is better able to pay for it, and cleaner energy technologies are more developed.
Writing in the International Herald Tribune on Friday, the U.N. head said the world was "on the verge of a catastrophe if we do not act."
However, he insisted that he remained optimistic that international cooperation could still help reverse the damage caused by unchecked temperature rises.
"The overarching message: We can beat this. There are real and affordable ways to deal with climate change," he said in the column. E-mail to a friend
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