VALENCIA, Spain (AP) -- Climate negotiators from 145 countries and leading scientists opened a weeklong conference Monday to complete a concise guide on the state of global warming and what can be done to stop the Earth from overheating.

Environmentalists and authors of the report expected tense discussions on what should be included and what is being left out of the last of four UN reports to be issued this year by the Intergovernmental Panel on Climate Change, co-winner of this year's Nobel Peace prize.
The document to be issued Saturday sums up in a few dozen pages the scientific consensus on how rapidly the Earth is warming and the effects already observed, the impact it could have for billions of people and what steps can be taken to keep the planet's temperature from rising to disastrous levels.
The summary will be negotiated line-by-line this week, then adopted by consensus.
UN Secretary General Ban Ki-moon was to attend the launch of the report, which will provide the factual underpinning for a crucial meeting next month in Bali, Indonesia. That conference will begin exploring a new global strategy 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.
Janos Pasztor, of the UN Environmental Program, a parent body of the IPCC, said this week's report will be the one document that the thousands of delegates at Bali ""will be packing in their suitcases and carrying in their back pockets.""
This week's report will be the first to include a brief chapter on ""robust findings and key uncertainties,"" in which the authors pick out what they believe are the most relevant certainties and doubts about climate change.
""We summarize which kind of things we are very confident in and what is much less certain. That can be quite a complex discussion,"" said Bert Metz, one of some 40 authors. Some delegations want to stress certain points that others would prefer to avoid, he said.
Among the uncertainties cited in an early draft obtained by The Associated Press: the lack of data from key areas of the world, conflicting studies on the effects of cloud cover and carbon soaked up by oceans, and projections on how planners in developing countries will factor climate change into their decisions.
The IPCC already is under criticism for the selectivity and language of the policy summaries, which have been softened on several points because of objections by countries such as the United States, China and some big oil-producing nations like Saudi Arabia.
On Monday, WWF, one of several environmental groups invited to observe the process, said ""governments cut vital facts and important information"" during the negotiations.
Without naming them, the WWF accused governments with ""politically inspired trimming"" of facts from the summaries, which it said diluted the urgency to make deep cuts in emissions of carbon dioxide and other greenhouse gases.
Scientists say the full reports on which the summaries are based — each comprising more than 1,000 pages — remain valid, and that their own presence during the discussions ensures the scientific integrity of the summaries.
Yvo de Boer, the U.N.'s top climate official, said getting governments to sign off on the summaries is a critical element of the IPCC's value.
""Because those reports are adopted by governments, there is no government that can now stand up and say, 'I don't accept what's in the IPCC report.' That means that you have a common scientific base,"" he said in an interview Friday.
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. ___