Running well behind schedule, top global warming experts huddled Thursday for a last day of talks with bureaucrats from more than 100 countries on a closely watched report that could influence government and business policy worldwide.
The scientists and government officials worked behind closed doors until well past midnight Wednesday and planned another late night session Thursday to finish the report in time for its Friday morning release.
Some expressed concern that the 12- to 15-page document would be too cautious, since participants must reach consensus on each word.
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The report from the Intergovernmental Panel on Climate Change will warn the world that global warming is here and worsening, using its bluntest language yet. It is the fourth such report since 1990.
According to drafts and participants, the document says it is "very likely" — which means at least 90 percent certain — that climate change is caused by humans burning fossil fuels, and will result in a temperature increase of between 2.5-10.4 F by the year 2100.
Some participants apparently want to change that wording to "virtually certain," which connotes a 99 percent likelihood.
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"People seem to be feeling, let's make sure that the text actually means something and makes sense to the people it's intended for," Catherine Pearce of Friends of the Earth, who is observing the talks, said Wednesday night.
"Some are saying there's no point in having texts that ... don't say anything, that are so watered down," she said.
The talks were far behind schedule, held up by debate over nuances of language, delegates told The Associated Press on Wednesday. That was before the group delved into the most contentious questions, including predictions of how much sea levels will rise.
A Russian participant, who did not want to be named because the talks are confidential, said the sea level discussions were complex and had not reached a conclusion by Wednesday evening.
Scientists are trying to incorporate concerns that their early drafts underestimate how much the sea will rise by 2100 because they cannot predict how much ice will melt from Greenland and Antarctica.
In early drafts, scientists predicted a sea level rise of no more than 23 inches by 2100, but that does not include the ice sheet melts.
Also, for the first time, the climate panel says stronger hurricanes and cyclones since 1970 are "more likely than not" linked to global warming, according to a draft. That could change, however, since the issue is hotly debated in scientific circles.
One participant, who asked not to be identified, said there was a noticeable change in the U.S. delegation, which some accused of hanging up the 2001 talks: "The U.S. is much more constructive."
Negotiators are staring at a countdown clock showing them how far behind they are. The report is being edited in English, then must be translated into five other languages.
Later Thursday, Paris monuments including the Eiffel Tower and concerned citizens in several European countries were expected to switch off their lights for five minutes to call attention to energy conservation, heeding a call by French environmental campaigners.
Some experts said that while well-intentioned, the lights-out could actually consume more energy than it would conserve by requiring a power spike when the lights turn back on — possibly causing brownouts or even blackouts.