VALENCIA, Spain - Delegates from more than 140 countries agreed Friday on a scientific “instant guide” for policy makers, stating more forcefully than ever that climate change has begun and threatens to irreversibly alter the planet.

The document, summarizing the scientific consensus on human-induced climate change, will be distributed to delegates at a crucial meeting in Indonesia next month that is intended to launch a political process on international cooperation to control global warming.

Five days of sometimes tense negotiations ended before dawn with the approval of a 20-page summary of thousands of pages of data and computer projections compiled over the last six years by the Nobel Peace prize-winning Intergovernmental Panel on Climate Change.

The report does not commit participating governments to any course of action but it is important because it is adopted by consensus, meaning those countries accept the underlying science and cannot disavow its conclusions. It provides a common scientific base line for the political talks.

“This is a groundbreaking document that will pave the way for deep emissions cuts by developing countries,” said Stephan Singer, a climate specialist for the World Wide Fund for Nature.

The report describes how climate systems are changing and why, the effects it is having on mankind and ecosystems, and various scenarios of future impacts, depending on how quickly action is taken to slow the trend.

The summary and a longer “synthesis report” were expected to be formally adopted after proofreading. They will be released Saturday at a news conference attended by U.N. Secretary-General Ban Ki-moon.

“Warming of the climate system is unequivocal,” the summary begins, in a statement meant to dispel any skepticism about the reality of climate change, said participants in the meeting.

In a startling and much-debated conclusion, the document warns that human activity risks causing “abrupt or irreversible changes” on Earth, including the widespread extinction of species and a dramatic rise in sea levels before the end of this century, they said on condition of anonymity because the details are supposed to remain confidential until today.

“I think overall it is a good and balanced document,” said Bert Metz, an eminent Dutch scientist and one of the 40 authors of the draft. “In the end, a lot of people had to compromise,” he said.

Though it contains no previously unpublished material, the summary pulls together the central elements of three lengthy reports the IPCC released earlier this year. Boiling down the 3,000 pages into about 20 was “quite a challenge,” said Metz.

The agreement was seen as a personal triumph for the IPCC chairman, Rajendra Pachauri of India, who presided with no-nonsense efficiency and bulldozed through compromise language. Pachauri, who will accept the IPCC’s Nobel Peace prize in Oslo on Dec. 10 along with former U.S. Vice President Al Gore, is expected to stand for re-election as head of the IPCC next year, delegates said.

Delegates said the talks this week were difficult, and sometimes bogged down for hours over a brief phrase.

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 five years. Kyoto obliges 36 industrial countries to radically reduce their carbon emissions by 2012, but has no clear plan for what happens after that date.

Organizers say the new “road map” emerging from Bali should draw in the United States, which rejected the Kyoto accord and has tried to enlist other countries in voluntary schemes to reduce emissions of greenhouse gases and invest in technology research.

Participants in the Valencia meeting said the U.S. delegation questioned the most hard-hitting statements in the summary that implied the urgency of reining in carbon emissions. But the final text retained key language, they said.