The first worldwide demonstration on climate change will coincide with the opening of a key United Nations conference to set out the basis for the reduction of greenhouse gases after the Kyoto treaty expires in 2012.
Organisers of the protests warned that the world's leading industrialised nations had failed to make an impact on climate change and some, in particular Britain, were backsliding on their environmental commitments.
The UN meeting in Montreal, which will be attended by representatives of 189 countries, is set to be dominated by efforts to persuade America - the world's largest carbon emissions producer - to join future UN-led talks on ways to curb rising temperatures and sea levels.
The Bush administration has refused to ratify the Kyoto agreement, which pledges the 35 leading industrialised nations to cut carbon dioxide levels to 5.2 per cent below 1990 levels between 2008 and 2012 - an undertaking they are struggling to meet.
In the context of Washington's steadfast refusal to contemplate any "binding" climate change commitments and signs that Kyoto is failing to cut greenhouse emissions, environmentalists believe a show of mass public discontent will send a powerful signal to the climate talks.
Phil Thornhill, of the London-based Campaign Against Climate Change, who originated the idea for the demonstrations, said: "It is a massive opportunity for ordinary people to show that urgent action is needed if we are to prevent a catastrophic destabilisation of the climate. We are in a race against time and, if anything, world leaders seem to be going backwards. These protests must send the message that this is the very last thing we need. Never before have we been able to do that with a single worldwide voice."
The centrepiece of the International Day of Climate Protest will be a mass protest in Montreal, where at least 15,000 people are expected to lobby delegates, including Britain's Environment Secretary, Margaret Beckett, for a globally binding climate agreement after 2012.
The protest in London, which is expected to draw similar numbers, will pass the offices of the American oil giant Exxon Mobil and the embassy of Australia, which has also refused to ratify Kyoto, before ending with a rally outside the American embassy in Grosvenor Square.
Across the world similar protests will be held in locations from Helsinki to Seoul. In Washington, drivers of fuel-efficient hybrid cars will rally around the White House while in New Orleans - devastated by Hurricane Katrina in August - there will be a "Stop Global Warming" street party in the French Quarter.
But despite the worldwide show of popular unity, there is pessimism that the 10-day UN meeting will break new ground in achieving a successor to the Kyoto treaty which will also include developing nations and the two countries expected to become the world's two biggest producers of carbon emissions by 2050 - China and India.
Ms Beckett this week showed the level of governmental expectation by describing those expecting new Kyoto-style targets to be agreed as "living in cloud-cuckoo-land". Even the original Kyoto agreement is failing to meet expectations. In 11 European Union countries emissions have grown, not shrunk. In Japan, emissions are nearly 18 per cent above target while in Canada - host of this week's meeting - the gap is almost 30 per cent.
Despite hopes among the Canadian and EU delegations, led by the British presidency, that the Bush administration can still be coaxed into the talks process, Washington has already bluntly ruled out any new commitments - pointing instead to a voluntary undertaking to cut greenhouse emissions by 18 per cent by 2012.
Instead the only proposal creating a buzz around the conference building this week was the idea, championed by Papua New Guinea, for wealthy countries to pay developing nations to preserve rainforests by not cutting down trees. The loss of tropical forest accounts for 20 per cent of carbon emissions by reducing the amount of carbon dioxide filtered from the air.
While such a scheme would represent progress, activists warn that the big picture - binding targets to achieve a net reduction in greenhouse gases which will include the US, China and India - is in danger of slipping away. Mr Blair was last month accused of moving away from the Kyoto model towards the stance of his key ally George Bush when he called for a focus on technology - from renewable energies to nuclear power - to reduce emissions.
George Monbiot, the academic and leading environmental commentator, who will address the London rally, said: "There is probably very little we can expect [from Montreal] because we are doing nothing to keep fossil fuel in the ground. All these techno-fixes are a waste of time if we continue to burn fossil fuel at the same rate.
"There is a lot of cynicism about what the British government is doing. Tony Blair has promised much and persuaded many that he will deliver but it has turned out to be rubbish. Blair had no intention of doing anything on climate change other than talk about it.
"But this weekend's protests are taking place in a changed context - the media are listening and finally we have to make the politicians listen."
* LONDON Midday - 3.30pm
Depart Lincoln's Inn Field, passing ExxonMobil offices, Australian embassy, and Downing Street - where a letter will be delivered demanding assurances that Britain will adhere to Kyoto-style targets. A rally will be held in Grosvenor Square, outside the American embassy. Speakers include Michael Meacher, former environment secretary, and George Monbiot.
* OTHER COUNTRIES
Australia, Bangladesh, Brazil, Bulgaria, Canada, Chile, Croatia, Democratic Republic of Congo, Finland, France, Germany, Greece, Indonesia, Republic of Ireland, Italy, Japan, Mexico, New Zealand, Nicaragua, Norway, Peru, Phillipines, Portugal, Romania, Russia, South Africa, South Korea, Spain, Turkey, Uganda, United States, Venezuela.Reuse content