The hundreds of atmospheric scientists, oceanographers, ice specialists, economists, sociologists and myriad other experts who make up the IPCC are tasked with being neutral and balanced.

They are required to draw conclusions only on what is known and proven, and to be open and honest about areas where there is doubt, ignorance or debate.

Almost unknown to the general public, the IPCC has issued only three of these "assessment reports" since its inception -- but each has had huge repercussions.

These effects might take months or even several years to happen.

But what starts with an anonymous panel of scientists cascades across society.

It shapes government policies, influences corporate strategies and lifestyle decisions by individuals -- and gives the political cauldron a powerful stir.

The IPCC comprises three working groups of men and women, nominated by governments and international organisations, who are experts in their particular field.

They trawl through peer-reviewed and published literature and summarise these findings; the IPCC does not conduct research of its own.

Working Group 1 -- whose report will be unveiled in Paris on February 2, after a four-day plenary meeting -- updates knowledge about the scientific basis for climate change.

Working Group 2 deals with the likely impacts of climate change; its members meet in Brussels from April 2-5. Working Group 3 looks at efforts to lessen carbon pollution and adapt to climate change; it meets in Bangkok from April 30 to May 3.

Each group may assess thousands of studies.

Their summary draft undergoes a two-stage review by outside assessors and governments before being submitted to a plenary, when it can be vetted line by line or even word by word before the final version is approved by consensus.

This exhaustive approach by the finest minds, the weighing of the facts and quest for balance are what gives the IPCC its clout.

Each Working Group report comprises two main sections -- a lengthy scientific-technical resume plus a "summary for policymakers" of about 50 pages. The process is rounded off in a synthesis report, to be agreed this year at a meeting in Valencia, Spain, from November 12-16.

Despite its strong reputation, the IPCC's brief history has not been without controversy.

Robert Watson, a leading British-American scientist who was frequently outspoken about climate change, was ousted as its chairman in 2002 after only one term.

Sources at the time said pressure from the Bush administration forced Watson out. Watson was replaced by a vice chairman, Rajendra Pachauri, a respected Indian science administrator.

The IPCC has a small secretariat, hosted at the WMO in Geneva.

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