By Environment Correspondent Alister Doyle
STOCKHOLM (Reuters) - A U.N. panel of global climate scientists were set to work through Thursday night to ensure that their strongest case yet for man-made global warming would make sense to the widest possible audience.
Drafts show that the Intergovernmental Panel on Climate Change (IPCC) is set to pronounce that most of the warming of the Earth's surface since the 1950s is "extremely likely" -- at least 95 percent probable -- to be man-made. At its last meeting in 2007, it put the probability at 90 percent, and in 2001 it was 66 percent.
The 30-page summary that the IPCC produces, the first of four about global warming in the coming year, is intended to be the main point of reference on the science of climate change for governments trying to develop their response to global warming.
Delegates said the tone was constructive, with countries urging better explanation of scientific findings, not challenging them as the basis for cuts in greenhouse gas emissions.
Most of the discussions were about how best to describe a world set to suffer more heatwaves, downpours and floods as well as higher sea levels as temperatures rose, they said.
"The tone is surprisingly good," one delegate said, speaking on condition of anonymity since the meeting is behind closed doors. "It's all about: 'Can't we write this sentence more clearly?'."
The document, which will also seek to explain a slowdown in the pace of warming this century, is meant to be presented in Stockholm on Friday at 10 a.m. (0400 ET).
At one point on Thursday, originally meant to be the fourth and final day of the negotiations, a display at the meeting showed that 85 percent of the time had elapsed but only 55 percent of the work had been done, one delegate said.
Some countries also wanted to stress that it was also "virtually certain", or at least 99 percent probable, that natural variations in the climate were not the sole cause.
Still, skeptics have said a slowing of the pace of warming this century, after fast gains in the 1980s and 1990s, is a sign that global warming may not be as urgent a problem as previously believed. The IPCC report slightly cuts the likely warming impact of a build-up of carbon dioxide on the atmosphere.
Scenarios in the drafts predict the hiatus will not last, however, and that temperatures will rise by between 0.3 C (0.5F) and 4.8 degrees Celsius (8.6 Fahrenheit) this century. The lower end of the range will only be possible with emissions cuts deeper than anything that major economies have said they are prepared to tolerate.
The report will face extra scrutiny after the IPCC made errors in its 2007 report, including an exaggeration of the melt rate of Himalayan glaciers. An outside review of the IPCC found that the mistake did not affect its main conclusions.
Almost 200 governments have agreed in principle to limit global warming to a maximum rise of 2 degrees C (3.6F) above pre-industrial times and have promised to work out a U.N. deal to limit their emissions accordingly by the end of 2015.
Separately, an academic study said people reacted best to the challenge of climate change if it was not presented as doom and gloom.
"The best way to encourage environmentally friendly behavior is to emphasize the long life expectancy of a nation, not its imminent downfall," according to the study of 131 nations led by NYU Stern Professor Hal Hershfield.
Over the next year, the IPCC will issue three more reports, about the impacts of climate change around the world, the possible solutions, and finally a summary of all the findings.
(Reporting By Alister Doyle)