Lord Robert May, president of the Royal Society, issued the warning as the UN meeting got underway in Montreal.
"The impacts of global warming are many and serious: sea-level rise ... changes in availability of fresh water ... and the increasing incidence of extreme events -- floods, droughts, and hurricanes,” Lord May said.
“The serious consequences of which are rising to levels which invite comparison with weapons of mass destruction," Lord May added, in an advance copy of his speech released to coincide with the UN conference.
Kyoto’s fate
It’s the first meeting since the Kyoto Protocol, the UN’s treaty for curbing greenhouse gases, took effect on January 16.
The 12 day talks will decide the fate of the protocol, signed by 156 countries.
But the agreement does not include fast-growing developing countries, such as China and India.
And Australia and the world’s worst polluter, the United States, are another two notable non- signatories.
US President George W Bush argues Kyoto penalises the oil-dependent US economy.
Host Canada has expressed hopes of easing a dispute between the US and Australia, and other countries on ways to combat global warming.
But Harlan Watson, the chief American negotiator at the climate change talks, says the Canadian approach, so far, is unacceptable.
“We're going to resist it absolutely and we've made that clear on a number of levels to the Canadian government. We feel very strongly, it's not appropriate. The ground is not there yet.
“There are many, many different ideas. People are not yet ready to move ahead under the convention. Kyoto parties though ought to be able to move ahead under the protocol,” he said.
Greenpeace spokesman, Steven Tindale, says the talks must not be stalled because of two countries.
“The important thing is that those countries that have ratified the Kyoto protocol which is most of the world minus the United States and Australia that those countries do move ahead with a regime of binding targets beyond 2012.”
“If the Canadians then outside of that process want to talk to the Americans and the Australians then fair enough, there's nothing to be lost in that, as long as it's not allowed to hold up progress,” he said.
Help to curb emissions
Up to 10,000 delegates from 189 nations will look at ways to help big developing nations like China and India curb their emissions.
"Everybody understands the problem but there are big differences on the solutions," Canadian Environment Minister Stephane Dion said of global warming.
Friends of the Earth has warned that the window of opportunity to act 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.
Observers are gloomy about the prospects of the Montreal talks of coming up with a post-2012 deal, that satisfies everybody.
But Lord May said the convention could help by agreeing to a pollution analysis that calculates the potential costs of corrective action - and the fallout if nothing was done.
"We need countries to initiate a study into the consequences of stabilising greenhouse gas concentrations at, below, or above twice pre-industrial levels, so that the international community can assess the potential costs of their actions or lack of them,” he said.
"Such an analysis could focus the minds of political leaders, currently worried more about the costs to them of acting now than they are by the consequences for the planet of acting too little, too late," Lord May said.
Regions uninhabitable
Lord May pointed to Hurricane Katrina, which devastated the US city of New Orleans in August, as an example of what could happen more often if global warming wasn’t tackled.
“Studies undertaken before the storm suggested rising sea temperatures would mean more severe hurricanes,” Lord May said.
"The estimated damage inflicted by Katrina is equivalent to 1.7 per cent of US GDP this year, and it is conceivable that the Gulf Coast of the US could be effectively uninhabitable by the end of the century," he said.
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.