Bedevilled for years by bitter negotiations and a US walkout, Kyoto will take effect just under three months from now, after Russia, in a ceremony in Nairobi, handed the UN legal instruments declaring it had ratified the accord.

The handover makes it possible "for the protocol to enter into force... 90 days from tomorrow (Friday), on 16 February 2005," United Nations Secretary General Kofi Annan said, after he received the document.

"This is a historic step forward in the world's efforts to combat a truly global threat," he added.

The move comes nearly seven years after Kyoto's framework was agreed by the UN Framework Convention on Climate Change (UNFCCC) -- the offshoot of the 1992 Rio Summit designed to tackle Earth's worsening environmental crisis.

It took four further years of haggling to decide Kyoto's rulebook, a thick and complex volume that includes several revolutionary, but never-tested, ideas for combatting global warming.

During that time, Kyoto's political future was almost destroyed by US President George W. Bush.

In March 2001, in one of his first acts after taking office, Bush said his country, even though it had signed the 1997 framework agreement, would not ratify the outcome.

He said the cost of meeting Kyoto's commitments would be too high for the US economy, dependent on the oil, gas and coal whose burning releases carbon dioxide gas, causing a "greenhouse effect" that is causing the atmosphere to warm.

Bush also branded Kyoto as unfair, because only industrialised nations -- and not fast-growing developing ones such as India and China which are now big polluters -- have to make targeted emissions cuts under the pact's timeframe.

Developing countries are being given financial help to avoid joining the path of fossil pollution and to help cope with the effects of climate change.

US abandonment stripped Kyoto of the world's biggest producer of greenhouse gases, accounting by itself for a quarter of the global total.

Only adroit action by the EU saved the treaty, but even so, Russia's ratification remained necessary for Kyoto to take effect.

Its clauses require a minimum threshold of ratification by polluting industrial signatories for it to be transformed from a draft agreement into a full-fledged treaty.

Only four industrialised countries -- the microstates Liechtenstein and Monaco, plus Australia and United States -- now remain outside Kyoto.

The 30 industrialised countries that have ratified it will now be legally bound to meet specific targets of reducing or limiting emissions of six carbon gases by a timeframe of 2008-12.

Joke Waller-Hunter, executive secretary of the UNFCCC's secretariat, said that Russia's ratification means "a period of uncertainty has closed."

"Climate change is ready to take its place at the top of the global agenda," she said in a statement released by the UNFCCC in Bonn.

But she called on the US "and other major emitters without Kyoto targets" to join the fight against global warming.

"The most up-to-date scientific research suggests that humanity's emissions of carbon dioxide and other greenhouse gases will raise global average temperatures by 1.4-5.8 C (2.5-10.4 F) by the end of the century," Waller-Hunter said.

"They will also affect weather patterns, water resources, the cycling of the seasons, ecosystems and extreme climate events."

If the 30 countries all achieve their goals, the industrialised world's carbon pollution will be reduced only by a couple of percentage points by 2008-2012, compared with the 1990 benchmark, according to some estimates.

In the meantime, big developing countries, which are not committed to any cuts, have continued to see huge rises in pollution.

Scientists say a 60-percent cut is needed by the middle of this century -- a task that, without a technological revolution, can only be addressed by post-Kyoto deals beyond 2012.

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