U.N. Report: Global Warming Could Be 'Abrupt, Irreversible'

Climate change is here, and it's getting worse, the year's final report by a U.N. panel will say when it's officially released Saturday.

"Warming of the climate system is unequivocal," the Intergovernmental Panel on Climate Change's Summary for Policymakers begins in a statement meant to dispel any skepticism about climate change.

It goes on to say that global warming could lead to "abrupt and irreversible" results, such as the widespread extinction of species, according to persons familiar with the final draft who requested anonymity because the summary was not yet public.

• Click here to visit FOXNews.com's Natural Science Center.

Working until dawn Friday, negotiators hashed out week-long disputes on the language, one of its authors said.

Provisional agreement on the text — which is about 20 pages and summarizes thousands of pages of data and projections — required compromises among the more than 140 delegations, but resulted in a "good and balanced document," said Bert Metz, a Dutch scientist who helped draft the report.

The brief Summary for Policymakers is expected to get final approval later Friday after a longer version of about 70 pages is reviewed and adopted.

It is to be released at 11 a.m. Spanish time Saturday — 5 a.m. EST — by U.N. Secretary-General Ban Ki-moon. Until then, the text is supposed to remain confidential.

The paper will be an "instant guide" to policymakers at a critical meeting next month in Indonesia, which could launch a round of complex talks on a new international accord for controlling carbon emissions and other human activity that is heating the planet.

Though it contains no previously unpublished material, the summary pulls together the central elements of three lengthy reports released earlier this year by the IPCC.

They describe observations of the changing climate, the potentially disastrous impacts of global warming and the tools available to slow the warming trend.

The document "is a clear message to policymakers," said Hans Verolme, of the World Wide Fund for Nature, one of the environmental groups acting as observers. "The scientists have done their job. They certainly deserved the Nobel Prize. Now the question is, what are the policymakers going to do with it?"

The panel shared this year's Nobel Peace Prize with Vice President Al Gore.

The meeting in the Indonesian resort of Bali starting Dec. 3 will discuss the next step in combating climate change after the measures adopted in the Kyoto Protocol expire in 2012.

The Kyoto accord, negotiated in 1997, obliges 36 industrial countries to radically reduce their carbon emissions by 2012, but has no clear plan for what happens after that date.

Though the United States rejected the Kyoto accord, it will attend the Bali meeting.

Participants in the Valencia meeting said the U.S. delegation questioned the most hard-hitting statements in the summary. But key language remained.

Delegates fought long and hard for the inclusion of issues of special interest to them: mountainous countries wanted a reference to melting glaciers; island states wanted to include warnings that oceans are becoming more acidic; poor countries insisted on firm language on "adaptation," implying international funding to help them cope with the effects of global warming.

The IPCC reports draw on the research of thousands of scientists and is reviewed by about 2,500 experts, then distilled and drafted by several hundred authors.

Metz said the discussions that began Monday were "contentious in a number of places," and required compromise language. "If I had written it myself, I might have done it a bit different," he said, though he added he was satisfied with the outcome.

"It says in crisp language: This is the problem, and this is what we can do to stop it," said Verolme, the WWF campaigner.

The Associated Press contributed to this report.