The most important report on the science of climate change for six years is set for release on Friday 2 February, and leaks suggest it will be an alarming read.

The minimum predicted temperature and sea level rises will jump, according to media reports, while the blame will be pinned firmly on greenhouse gas emissions from human activities. Its leading line is expected to be "there is a 90% chance humans are responsible for climate change", mostly due to the burning of fossil fuels.

That contrasts with the last version of the Intergovernmental Panel on Climate Change's report, issued in 2001, which concluded there was a 66% chance that humans were responsible for rising temperatures.

The new IPCC report is expected to predict that temperatures will rise by 2.0°C to 4.5°C by 2100. The 2001 report gave a range of 1.4°C and 5.8°C - a wider range and a lower minimum rise.

Similarly, the new report is believed to predict that sea-levels will rise by between 28 centimetres and 43 cm by 2100, compared with the 2001 prediction of between 9 cm and 88 cm (2.54 cm = 1 inch).

But even these changes are regarded by some as a conservative estimates arrived at by consensus. "If the IPCC comes out with significantly less than 100 cm of sea level rise, there will be people in the science community saying we don't think that's a fair reflection of what we know," said Bob Corell, chairman of the Arctic Climate Impact Assessment, speaking to Associated Press.
Gold standard

The IPCC draws together hundreds of the world's leading experts on climate science, under the auspices of the World Meteorology Organization and the UN Environment Programme, to review and assess all available research.

The result of their assessment, which is done every five to six years, establishes what is considered the gold standard of consensus on climate change science.

The new IPCC report was written by 1250 experts and reviewed by a further 2500. It is being released in stages during 2007. The first chapter, due on 2 February, deals with the scientific basis for climate change. This includes, for example, how the atmosphere responds to increasing levels of greenhouse gases, how the gases cycle through the environment, and changes in water temperature and sea-levels.

The final amendments to the drafts will be made at a meeting in Paris, France, starting on Monday. For four days, government officials will work line by line through a summary aimed at policymakers before they release it to the public on the morning of 2 February.
Melting fast

"I hope this report will shock people and governments into taking more serious action as you really can't get a more authentic and a more credible piece of scientific work. So I hope this will be taken for what it's worth," said the IPCC chairman, R K Pachauri.

Pachauri told Reuters that the report's findings will be "far more serious and much more a matter of concern" than in previous reports.

For instance, it was previously thought that it would take hundreds of years for the Greenland ice sheet to melt right the way through. But research published in 2002 showed that how the Greenland ice sheet was melting had been poorly understood. In 2006, satellite data suggested the ice sheet was disappearing three times faster than previously thought.

It is not yet known how much weight results like this will be given in new IPCC report. However, it is certain that a great number of high-profile scientific studies have painted a bleaker picture of human-induced climate change in the past six years.
Mitigating impact

One notable study came in December 2004. It looked at how human greenhouse gas emissions had affected the probability of a devastating heat wave in Europe in the summer of 2003 (estimated to have killed at least 35,000 people.) The study found that emissions from human activities at least doubled the risk of such an event.

The next two parts of the IPCC's 2007 assessment, plus a synthesis, will be released throughout the year. Part 2, dealing with the impacts of climate change and our vulnerability to those impacts, will be released in April. Part 3, to be released in May, deals with how we can mitigate these impacts.