It will be the first knowledge review by the UN's Intergovernmental Panel on Climate Change (IPCC) since 2001 -- and the phone-book-sized report will convey an unvarnished message that will be bleak and quite possibly terrifying.

Those close to the IPCC say it will not only confirm the grim warnings of the past but also amplify them. It will declare that climate change is already on the march -- and newly-discovered mechanisms in the complex climate system could worsen the threat.

"The [temperature] trends that were expected will be unchanged," says Herve Le Treut, director of research at France's National Centre for Scientific Research (CNRS).

"But one can add positive feedbacks that weren't measured a few years ago. The range of possible risks and awareness of them has widened."

In its 2001 report, the IPCC projected that global mean temperatures would rise by between 1.4 and 5.8 C (2.5-10.4 F) by 2100 compared with their 1990 level, depending on the atmospheric levels of carbon pollution, which traps heat from the Sun.

That estimated temperature range will not change, if Le Treut's rough forecast of the IPCC findings is correct. However, the report will also warn of newly-found "positive feedbacks" -- in ordinary language, vicious circles -- that could accelerate and possibly worsen the effects of climate change.

These include the loss of polar ice and alpine snow cover, which drives up temperatures because of the loss of whiteness which reflects sunlight, and the gradual melting of Siberian permafrost, releasing gigatonnes of carbon that had been stored for millennia in the frozen soil.

The IPCC's 4th Assessment Report "is going to shock a lot of people," says Hans Verolme of the green group WWF.

The long-awaited document comes on the heels of a string of studies in the world's science journals in 2006 that pointed to Greenland's shrivelling icesheet, loss of Antarctic glaciers, acidification of the ocean by absorption of CO2 and hammer blows to biodiversity as species habitat shifts or is destroyed.

Added to that was the report by British economist Sir Nicholas Stern, which highlighted the cost of failing to tackle greenhouse gas pollution.

If no action is taken on emissions, there is a more than a 75-percent chance that global temperatures will rise by between two and three degrees Celsius (3.6-5.4 F) over the next half century, an increase that would slash global economic output by three percent, the Stern Report said.

Overall, public awareness about climate change is rising all the time -- but this contrasts starkly with the action being taken by politicians.

The annual conference of the UN Framework Convention on Climate Change (UNFCCC), which took place in Nairobi in November, was a dreary circus of showy rhetoric.

The meeting, as expected, stood by the Kyoto Protocol for curbing greenhouse gases.

But it did almost nothing concrete for determining how this treaty -- burdened by its own complexities, weakened by a US walkout -- could deliver much faster, far deeper pollution cuts for the future.

That goes to the core of the problem.

Scrapping or modifying dirty carbon-spewing power stations and vehicles costs money, and people are loth to make sacrifices if they suspect competitors are getting a free ride.

Despite this, 2006 also saw the undercurrent of coming political change, most notably in the United States, the world's No. 1 polluter.

California vowed to cap its carbon emissions by 2020 in line with Kyoto's 1990 benchmark and sued automakers for damage to the state's climate system.

And, after their crushing victory in the US Congressional elections in November, the Democrats vowed to initiate climate-change legislation early next year.

Vicki Arroyo, director of policy analysis at a US think tank, the Pew Center on Global Climate Change, cautions that the incoming two-year Congress is relatively moderate.

It is likelier to go for a gradualist approach, implementing "climate-friendly" laws that nibble at President George W. Bush's voluntary approach on carbon emissions rather than bulldoze it away completely, she predicts.

"It may not be as sweeping as, for example, the EU [carbon] trading system -- yet," she said. "But it could lay the groundwork for a trading system, for example by requiring mandatory reporting of greenhouse gas emissions."

Other action could be new laws covering emissions by utilities or road transport, both of which would be sellable to the US public on the grounds that they save energy and thus reduce US dependence on imported oil, says Arroyo.

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