"People who have sent their delegates here want real progress," insisted Canadian Environment Minister Stephane Dion. "That's why here in Montreal, we have to get results."

The 12-day gathering of the UN Framework Convention on Climate Change (UNFCCC) is expected to draw between 8,000 and 10,000 participants from governments, businesses, science and green groups.

Its challenge will be to frame the first steps for crafting pledges on greenhouse-gas pollution after the present "commitment period" of the Kyoto Protocol runs out in 2012.

Sources close to the meeting expected the United States to take a hard line, pushing ahead with its demands for the gases to tackled by a voluntary approach, rather than by a legal cap, as is the case with Kyoto's present format.

The US delegation is expected notably to fight demands to spur negotiations for the post-2012 period.

Meanwhile, Lord May, the president of Britain's leading scientific body, the Royal Society, warned that global warming was an apocalyptic peril whose effects are already visible.

"The impacts of global warming are many and serious," May said in an advance copy of his speech released Monday, adding that the environmental problems wrought by greenhouse gases "invite comparison with weapons of mass destruction."

The environmental groups Greenpeace and Friends of the Earth warned that the window of opportunity was closing fast.

"Extreme weather events, drought and rising sea levels threaten the lives and livelihoods of millions of people around the world. Negotiators must remember this as they enter these talks," said Catherine Pearce of Friends of the Earth International.

Greenpeace campaigner Steve Sawyer said the meeting urgently had to give a sign that binding caps would remain post-2012, otherwise the world's fledgling market in carbon dioxide (CO2) emissions could be wrecked.

UN representative Richard Kinley urged industrialized nations to reduce their greenhouse gas emissions that are contributing to global warming.

But experts pointed out that developing countries like China and India will now have to contribute to anti-pollution controls.

The Montreal meeting is the first by the convention since the Kyoto Protocol, signed by 156 countries, took effect in February.

The pact commits industrialised nations to making specific cuts in carbon dioxide and five other greenhouse gases that trap solar heat, thus warming the planet's surface and disrupting its delicate climate system.

But the present commitment period does not include the planet's worst polluter, the United States, which walked away from the protocol in 2001 because of the high cost of meeting its Kyoto targets.

Nor does it include fast-growing developing countries, such as China and India, in its pledge on targeted reductions.

The present Kyoto period is only just a tiny first step towards tackling greenhouse gases that have increased dramatically in recent decades as fossil fuels are burned to power economic growth.

Atmospheric CO2 levels are now at the highest in 650,000 years, scientists say, and 2005 is likely to go into history books as the warmest year on record.

For post-2012 Kyoto to make serious inroads into this pollution, it would have to include the United States and big developing countries.

But finding a format that bridges this gulf of interests is a huge task. Negotiations are expected to last several years.

Canada is hosting the meeting amid domestic political upheaval, with Prime Minister Paul Martin's embattled minority government set to be ousted by a no-confidence vote in Parliament after months of acrimonious corruption allegations.

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