Tens of thousands of people are expected to join in demonstrations calling for action on climate change ahead of crunch UN talks.
World leaders will meet next week in Copenhagen with the aim of securing a new deal to tackle rising temperatures.
Environmental campaigners, aid agencies, trade unions and organisations including the Women's Institute are travelling to London from across the country to take part in "The Wave" to demand a strong deal on climate change.
Similar protests - all organised by the Stop Climate Chaos coalition - will also be taking place in Dublin, Belfast and Glasgow.
In London, an ecumenical service with an address by Archbishop of Canterbury Dr Rowan Williams will take place in Westminster Central Hall, before campaigners march from Grosvenor Square to Big Ben.
Meanwhile, there is a "climate emergency" bike ride being planned from Lincoln's Inn Fields. Hundreds of students will perform a "splash dance". Elsewhere, members of the Camp for Climate Action are planning to camp out at an as-yet secret location in the capital.
The march on Parliament will be led by an open-topped double decker bus, and will feature a ukulele-playing trapeze artist, cycling bishops, an 18ft long blue dragon and a coal monster. The Co-operative is supporting the protest and has chartered two trains from Manchester to London and one from West Yorkshire for its members to travel to the event, along with scores of buses from other locations.
The event, in which people are being asked to dress in blue, is being supported by pop group Blue's singer Antony Costa, who said: "Climate Change is the most important issue facing us all and so the politicians must get it right in Copenhagen."
The Stop Climate Chaos coalition, which includes groups such as Oxfam, Greenpeace, Friends of the Earth and WWF, is demanding the UK government increases its targets for EU-wide efforts to cut emissions.
Hundreds of nurses, hospital porters, social workers and home carers will join climate campaigners today to march on the Houses of Parliament to demand action to stop global warming.
Prior to next week’s crucial UN climate summit in Copenhagen, tens of thousands of people from all walks of life will march through the streets of London to demonstrate their support for a safe climate future.
The Wave march will call on world leaders to take urgent action to secure a fair international deal to stop global warming exceeding the danger threshold of 2?C.
Public-sector union Unison is calling for an official recognition of the role trade unions can play in fighting climate change.
“Key to helping countries cope with the worst effects of climate change will be increasing investment in their public sector,” a spokeswoman said.
Unison head of business and environment Mike Jeram explained that it was only right that world leaders commit to a “just transition” when they meet in Copenhagen.
“This must include green policies that are worker-friendly, including good green jobs and training,” he said.
“Key to tackling climate change is making sure people change their behaviour at work.
“Unions have a network of branches, reaching into workplaces all over the world. Using this network to promote efficient green practise would be a good place to start. Unison thinks this role should be officially recognised.”
He added: “Some countries will be hard hit by the effects of climate change. As a public-sector union, we know that these regions will need to step up their investment in public services such as disaster prevention, energy efficiency, healthcare and water management.
“We hope that world leaders will help make this possible in their negotiations.”
Join me and friends who are at the climate change demonstration as this one of the biggest event in the world followed by millions of people.
In an unprecedented move, 56 newspapers from around the world have today published a common editorial - "14 days to seal history's judgement on this generation" - aiming to speak with one voice to the leaders negotiating a deal at Copenhagen this week.
The papers signing up to the editorial include The Guardian, El Pais, The Miami Herald, Le Monde, The Toronto Star, The Brunei Times and 50 others from countries including Rwanda, Tanzania and Bangladesh.
Ian Katz of the Guardian, who largely coordinated the editorial, says the purpose of the joint editorial is to show:
"if all of us who disagree about so much can agree on what must be done, then surely you can too...If the editorial lacks the detail that will have to be cracked over the next 14 days in Copenhagen, it should be a source of encouragement that such a diverse coalition was able to agree about so much - not least the precariousness of our situation, and the need for Copenhagen to deliver a full treaty by summer 2010 at the latest."
The editorial says:
"Climate change has been caused over centuries, has consequences that will endure for all time and our prospects of taming it will be determined in the next 14 days. We call on the representatives of the 192 countries gathered in Copenhagen not to hesitate, not to fall into dispute, not to blame each other but to seize opportunity from the greatest modern failure of politics. This should not be a fight between the rich world and the poor world, or between east and west. Climate change affects everyone, and must be solved by everyone.
The science is complex but the facts are clear. The world needs to take steps to limit temperature rises to 2C, an aim that will require global emissions to peak and begin falling within the next 5-10 years. A bigger rise of 3-4C — the smallest increase we can prudently expect to follow inaction — would parch continents, turning farmland into desert. Half of all species could become extinct, untold millions of people would be displaced, whole nations drowned by the sea. The controversy over emails by British researchers that suggest they tried to suppress inconvenient data has muddied the waters but failed to dent the mass of evidence on which these predictions are based."
It continues:
"Social justice demands that the industrialised world digs deep into its pockets and pledges cash to help poorer countries adapt to climate change, and clean technologies to enable them to grow economically without growing their emissions...The transformation will be costly, but many times less than the bill for bailing out global finance — and far less costly than the consequences of doing nothing."
