A U.N. climate panel will project wrenching disruptions to nature by 2100 in a report next week blaming human use of fossil fuels more clearly than ever for global warming, scientific sources said.
A draft report based on work by 2,500 scientists and due for release on February 2 in Paris, draws on research showing greenhouse gases at their highest levels for 650,000 years, fuelling a warming likely to bring more droughts, floods and rising seas.
The report by the Intergovernmental Panel on Climate Change (IPCC) may have some good news, however, by toning down chances of the biggest temperature and sea level rises projected in the IPCC's previous 2001 study, the sources said.
But it will also revise up its lowest projections.
"The main good news is that we have a clearer idea of what we are up against," one source said. The report will set the tone for work in extending the U.N.'s Kyoto Protocol, the main international plan for curbing global warming, beyond 2012.
The IPCC will say it is at least 90 percent sure that human activities, led by burning fossil fuels, are to blame for a warming over the past 50 years.
The draft conclusion that the link is "very likely" would mark a strengthening from "likely" in the 2001 report -- a probability of 66-90 percent.
"Quite often much of the debate is 'what level of certainty do we have around some of these phrases?'," said Robert Watson, World Bank chief scientist who chaired the previous 2001 report.
Scientists and representatives of governments will meet in Paris from January 29 to review the draft and approve a text. Watson declined to predict any of the 2007 conclusions.
But the sources said the new report is likely to foresee a rise in temperatures of 2 to 4.5 Celsius (3.6-8.1 Fahrenheit) this century, with about 3 Celsius (5.4F) most likely.
The 2001 report said temperatures could rise by 1.4 to 5.8C (2.5-10.4F) by 2100 -- but did not say which end of the range was most likely. The IPCC would also narrow the 2001 forecast range of sea level rise of 9-88 cms (3.5-34.7 inches) by 2100.
Bjorn Lomborg, the Danish author of "The Skeptical Environmentalist", said the IPCC would discredit "the rhetoric of catastrophe" that he accused some governments of adopting.
"Yes, climate change is a problem but it's not this over-arching, civilization-destroying thing that the rhetoric of today is telling us," he said.
Even so, the European Union says any temperature rise above 2C (3.6F) will cause "dangerous" change, for instance with more heatwaves like in Europe in 2003 that killed 35,000 people.
"Even the minimum predicted shifts in climate for the 21st century are likely to be significant and disruptive," the U.N. Climate Secretariat says of the 2001 projection of a minimum 1.4C rise. It says the top of the range would be "catastrophic".
Temperatures have risen 0.6C (1.1 F) since 1900 and the 10 warmest years since records began in the 1850s have been since 1994. The world has warmed about 5C (9F) since the last Ice Age.
Benjamin Santer, a climate scientist at the U.S. Lawrence Livermore National Laboratory, said research in the last decade had expanded from studying surface temperatures to everything from ocean heat content to glacial retreat.
"The system is telling us an internally consistent story -- you can't explain the observed changes ... in the climate system over the second half of the 20th century by invoking natural causes," he said. He said he did not know the IPCC view.
© Reuters 2007.