Protesters have marched in London in support of the Kyoto Protocol, the international agreement on emissions coming into force on Wednesday.
The US - the world's biggest polluter - pulled out of Kyoto 2001
Police said about 500 people had marched to the United States embassy, carrying flags of the 136 countries that have ratified the treaty.
The US, the world's largest polluter, withdrew from the treaty in 2001, citing economic concerns.
The protocol, agreed in 1997, sets legally-binding emissions reductions.
Nearly 180 nations have signed up, but some have not yet formally ratified it.
It binds industrialised nations to reduce worldwide emissions of greenhouse gases by an average of 5.2% below their 1990 levels over the next decade.
The treaty nearly stalled after the US, which created 36% of emissions in 1990, pulled out.
The protocol needed to be ratified by countries who were responsible for at least 55% of the world's carbon emissions in 1990 to come into force. However, in 2004 Russia agreed to sign up, allowing that requirement to be met.
Phil Thornhill, of the Campaign Against Climate Change, which organised the march, said: "We want to express just how aghast we are the US is not joining the rest of the world.
"Scientists say we have about 10 years to save the environment, we really have to change the rate at which we act."
Green MEP Caroline Lucas said it was time to get tough with Washington.
"By refusing to sign up to Kyoto, the US is demonstrating - yet again - that it is a rogue state pursuing its perceived national self-interest to the exclusion of the peoples of the rest of the world.
"This is unacceptable and the world community must now look at ways of holding the US accountable for damage its isolationist policies are inflicting on the rest of the world," she added.
Friends of the Earth director Tony Juniper said: "We are here to protest against the Bush administration and celebrate the fact Kyoto will come into force this week, despite the Bush administration trying its hardest to kill it."
Lib Dems environment spokesman Norman Baker told the crowd it was "appalling" only 3% of energy in the UK came from renewable sources.
But Kendra Okonski of the International Policy Network, said the US was taking the right route.
"Kyoto is a very bad investment, because it is very costly today and only brings benefits far in the future.
"The US is correct in its decision of continuing to innovate and invest in new technologies that can bring us to a cleaner and more efficient future, for the whole world not just for the US or Europe."
In Edinburgh, campaigners held a "climate carnival" to highlight the effects of global warming.
Police said about 25 protesters turned out.
Some were dressed as mosquitoes, which they say are being found further north as climate change takes effect.