Canadian Prime Minister Paul Martin declared that climate change already gripped his country's far north, blasted skeptics who brush off global warming and told the United States to respect the "global conscience" on this issue.

"High in the Arctic, in our interior and along our coasts, the country we know is being transformed," Martin told the conference, which his country is hosting.

"Winters are growing milder, summers hotter and more severe, there is plant life where before there was none; there is water where before there was ice. Our permafrost is thawing, and releasing methane gas into the atmosphere."

He added: "Within short decades, the Northwest passage, the famously unnavigable thoroughfare of history, may be passable -- a striking and unsettling example of our delicate balance succumbing to untenable strain."

French President Jacques Chirac, in a video address, branded climate change "a brutal and urgent reality, the most serious threat weighing on the future of humanity."

"Even if scientific uncertainties remain, the accumulation of evidence, the visible changes to the environment, the multiplication of extreme (weather) events bear witness to a phenomenon that no-one can seriously contest any longer."

Ministers or their stand-ins from 189 countries and entities are meeting for three days, ending Friday, at the climax to a 12-day gathering focused on the Kyoto Protocol, the troubled UN pact on curbing greenhouse gases.

They are under mounting pressure to come up with a commitment for making deeper emissions cuts when the treaty's present pledges run out in 2012.

The conference is taking place under the UN Framework Convention on Climate Change (UNFCCC), the fruit of the 1992 Rio Summit.

Kyoto, its key offshoot, sets targets for industrialised countries to reduce carbon-based gases that act like an invisible blanket, trapping the Sun's heat and driving up the planet's surface temperature.

The protocol took effect last February after a long and agonising gestation marked notably by the walkout of the United States in 2001.

But the absence of the world's No. 1 polluter is not the only problem dogging Kyoto.

Under the present commitment period, only developed countries are required to cut pollutions as compared to a 1990 benchmark.

Big, fast-growing developing countries such as China and India are exempt, even though they are becoming huge polluters in their own right.

As a result, Kyoto in its current format makes only the tiniest dent in a problem that is swelling by the year and desperately needs urgent redress.

Sources at the conference said there seemed widespread backing for a Canadian proposal to start two years of negotiations for a deal on how to achieve these deeper, long-range cuts and for action to be as wide as possible.

But exactly how to achieve these cuts and who would make them constitute a diplomatic minefield and are skirted in the proposal.

All the same, the United States bluntly voiced its objections to starting the talks and stood by its stance that goodwill and innovative clean technology would roll back greenhouse gases.

"It is our belief that progress cannot be made through these formalised discussions," Paula Dobriansky, US Under Secretary for Democracy and Global Affairs told a press conference.

"We believe that the best approach and the best way forward is one that takes into account diversified approaches and differing opinions. One size does not fit all."

In contrast to the US emphasis on a voluntary approach and bilateral "partnerships" with developing countries, many ministers emphasised that global warming required a global response and defended the UN framework for achieving it.

Developing countries, gathered in a 132-nation group, said responsibility for fixing global warming lay primarily with the rich countries that had caused it by their reckless burning of fossil fuels.

"We should all make a contribution, depending on our respective economic capacities," said European Environment Commissioner Stavros Dimas, adding however "there must be a role" for developing countries.

Many scientists say the first effects of climate change are already kicking in, with the melting of Alpine and Himalayan glaciers and erosion of Arctic and Antarctic icesheets.

They also speculate that this year's unprecedented season of Atlantic storms, spearheaded by Hurricane Katrina which devastated New Orleans, was caused by global warming.

Tackling the pollution is a big headache because of the economic cost in requiring greater fuel efficiency and switching to cleaner energy sources.

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