More than 100 nations on the U.N. climate panel agreed a final text after all-night disputes during which some scientists accused governments of watering down some of their findings in a draft 21-page summary.
"We have an approved report," Rajendra Pachauri, the chair of the Intergovernmental Panel on Climate Change (IPCC), told reporters on Friday morning after negotiations about the regional impact of climate change that began Monday. Pachauri added that he hoped the world would pay attention. (See also: ".")
The report says the poor will be hardest hit by changes including desertification, drought and rising sea levels.
The IPCC is made up of 2,500 scientists and is the top world authority on climate change. Its findings will guide policy in coming years on issues such as extending the U.N.'s Kyoto Protocol, the main U.N. plan for capping greenhouse gas emissions, beyond 2012.
"Conflict is a hard word; tension is a better word," Gary Yohe, one of scientists who was a lead author of the report, told Reuters of the mood at the talks. (CNET News.com recently interviewed another co-author,, about the report.)
He said China, Russia and Saudi Arabia had raised most objections during the night. Other participants also said the United States had toned down some passages.
Some scientists objected, for instance, after China tried to eliminate a note saying that there was "very high confidence" that climate change was already affecting "many natural systems, on all continents and in some oceans."
China, the second largest source of greenhouse gases after the United States and ahead of Russia, wanted no mention of the level of confidence.
Still, delegates sharpened other sections, including adding a warning that some African nations might have to spend 5 to 10 percent of gross domestic product on adapting to climate change.
Overall, the report is the strongest U.N. assessment yet of the threat of climate change, predicting water shortages that could affect billions of people and a rise in ocean levels that could go on for centuries.
It builds on a previous IPCC report in February saying that human greenhouse gas emissions, mostly from burning fossil fuels, are very likely to be the main cause of recent warming.
That report also forecast that temperatures could rise by 3.2 degrees to 7.2 degrees Fahrenheit this century.
Friday's study also says climate change could cause hunger for millions with a sharp fall in crop yields in Africa. It could rapidly thaw of Himalayan glaciers that feed rivers from India to China and bring heat waves for Europe and North America.
U.S. delegates rejected suggested wording that parts of North America may suffer "severe economic damage" from warming.
But it toughened some sections by saying "significant loss of biodiversity" was possible in parts of Australia such as the Great Barrier Reef by 2020.
The IPCC report said climate change is no longer a vague, distant threat.
"The whole of climate change is something actually here and now rather than something for the future," said Neil Adger, a British lead author of the report.