If there's one document on global warming policymakers might put in their briefcase, this would be it. On Monday, scientists and government officials gather in Valencia, Spain to put together the fourth and last U.N. report on the state of global warming and what it will mean to hundreds of millions of people whose lives are being dramatically altered.

Unlike the past three tomes, this one will have little new data. Instead, it will distill the previous work into a compact guide of roughly 30 pages that summarizes complex science into language politicians and bureaucrats can understand.

It will be the first point of reference for negotiators meeting next month in Bali, Indonesia, to decide the future course of the worldwide push to curb greenhouse gas emissions after the 2012 expiration of the first phase of the Kyoto Protocol, the landmark agreement that assigned binding reduction targets to 36 countries.

The last of four reports by the Intergovernmental Panel on Climate Change "integrates all the elements, the connections between them," said one of its authors, Bert Metz, of the Netherlands Environmental Assessment Agency.

U.N. officials delayed the Bali meeting by several months until after the report is released, expecting it would add political momentum to the conference.

Though the IPCC was created in 1988 to assess the science of global warming, its work gathered a momentum this year that has helped reshape opinion in the public and governments.

In the ultimate validation, the IPCC's warnings of man-induced climate change shared the Nobel Peace Prize with former Vice President Al Gore, the world's best-known global warming campaigner.

"The reactions that I heard from politicians around the world is that they were shocked by the reports and that they should be acted on," said Yvo de Boer, the U.N.'s top climate official.

The United States, Australia and many developing countries that shunned the Kyoto treaty are now ready to begin discussing a successor agreement at the Bali conference, De Boer said.

"There is a growing consensus that Bali needs to achieve a breakthrough to put negotiations in place, and that's very encouraging," he said. "But it's not going to be a piece of cake."

The studies issued earlier this year painted a dire picture of a planet in which unabated greenhouse gas emissions could drive average temperatures up as much as 11 degrees by 2100.

Even a 3.6-degree rise could subject up to 2 billion people to water shortages by 2050 and threaten extinction for 20 percent to 30 percent of the world's species, the IPCC said.

While some people will go thirsty from lack of rain, millions more will suffer devastating floods; diseases will proliferate; the food supply may at first increase in some areas, but will plummet later; countries that are now poor will grow still poorer.

The scientists set out a basket of technological options to keep the temperature rise to the minimum, with investments amounting to about 3 percent of the world's gross domestic product — far less than what the IPCC said it would cost later to fix the damage caused by higher temperature increases.

Campaigners are looking for the final "synthesis report" to emphasize the action governments can take, the consequences of inaction and the brief time remaining to put that action into gear.

"We would want to emphasize the urgency which comes from the science," said Stephanie Tunmore of the Greenpeace environmental group. "We know what's happening, we know what's causing it, and we know what we have to do about it."

A draft report of about 60 pages — distilling the previous three reports totaling more than 4,000 pages — has been circulating for months to governments, environmentalists and scientists for comment. The authors gathered in Valencia last week to incorporate some of the comments into the final draft.

Starting Monday, delegations from 145 countries meeting in this Spanish Mediterranean city will review the Summary for Policymakers, the critical document that becomes the single most important reference for nonscientists.

Each line must be adopted by consensus — and sometimes the use of a single word can be heatedly contested.

The final document is due to be released Saturday. U.N. Secretary-General Ban Ki-moon's presence at the unveiling is meant to underscore its importance.

"I expect some scuffling over the final language," especially over the urgency and the level of certainty of some predicted events, said Peter Altman, of the Washington-based lobby National Environmental Trust.

Despite the haggling, the political input into a scientific document is essential, because governments cannot later disown it.

"After the summary is approved, it becomes the property of the governments," said Metz, who was one of about 40 scientists working on the final draft. "It becomes difficult for them to ignore the conclusions that they were subscribing to."

By ARTHUR MAX –
The Associated Press