Thousands of climate change campaigners have attended a rally in London, calling for world leaders to act urgently on the issue.
Organisers believed it would be the UK's biggest environment rally
The action included a march from the US embassy to Trafalgar Square, where celebrities joined a demonstration.
Some 22,500 people attended the rally, said the police while organisers said 25,000. There were no arrests.
Ashok Sinha, director of Stop Climate Chaos, said climate change was "the biggest threat the planet faces".
The rally comes ahead of UN climate change talks in Nairobi on Monday.
It also follows the publication of the Stern Review which suggested global warming could shrink the global economy by 20%.
Mr Sinha said: "I think people have realised that climate change is a humanitarian, a peace and security issue, an economic issue as much as it is a green issue and that's why we have such a diverse range of voices here today.
"It's a moral issue in the end and that's what I think is bringing people together."
He said the issue had brought together a broad coalition of groups, including traditional green activists, development organisations and charities.
Speakers at Trafalgar Square urged the government to push for a global treaty to cap global warming at 2C or less, as well as helping developing countries to adapt to climate change.
As the Stern Review was published last week, Chancellor Gordon Brown promised the UK would lead the international response to tackle climate change.
And Environment Secretary David Miliband said the Queen's Speech would feature a climate bill to establish an independent Carbon Committee to work with the government to reduce harmful emissions.
Musicians Razorlight and KT Tunstall and comedian Simon Amstell were among the celebrity names at Saturday's "I Count" campaign event.
Tunstall told the crowd she was very concerned about what was happening to the environment.
"We are screwing it up, we are making a real mess," she said. "Today is about raising awareness that we need to change our behaviour."
Joan Durran, 72, from Dorset, said she had joined the rally because she felt strongly about the issue.
"Climate change affects everybody," she said. "We're causing massive destruction and once something's lost you can't go back. "I'm here for my grandchildren because they're the ones who will really feel the effect."
The events were kicked off by cyclists who went on a "protest bike ride" to hand a petition into Downing Street calling for a tightening of annual emission targets.
But one of the UK's top climate scientists warned in a BBC News website article that, although climate change was "a reality", the language being used by some campaigners was becoming exaggerated and could weaken the arguments for policy change.
Mike Hulme, of the Tyndall Centre for Climate Change Research, also said he was concerned over the phenomenon of "catastrophic" climate change.
"That type of language is actually self defeating," he said. "What it does it disempowers - the language of fear and of terror and of anguish - it disempowers people."
But scientist and broadcaster Adam Hart-Davis told BBC Radio 4's Today programme that although the issue of global warming was raised more than 10 years ago, politicians had not acted.
"It may need this sort of hype and this type of meeting today to get the politicians off their backsides to actually do something," he said.
The United Nations Climate Change Conference will take place in Nairobi, Kenya, for two weeks from Monday.
The summit will look at what progress has been made by the Kyoto Protocol that requires industrial nations to cut their emissions.