Many experts said that time to slow a rise in temperatures widely blamed on burning fossil fuels was running out. A British report said the nation might resemble the tropics by 3000, with rising seas from melting ice swamping the coasts.
The United Nations, the European Commission and many environmental groups all urged tougher action beyond Kyoto, which entered into force on February 16, 2005 and runs to 2012.
"We need the full participation of all major emitting countries -- such as the United States, the world's leading economy, but also the world's leading polluter," European Commissioner Stavros Dimas said in marking the anniversary.
He warned that the world needed to strengthen action to contain global warming or would "run out of time to contain climate change." Most scientists say warming will bring a more chaotic climate with more heatwaves, droughts and floods.
NASA has said that 2005 was the warmest year at the earth's surface since records began in the 1860s. Another recent study showed that concentrations of greenhouse gases were at the highest in 650,000 years.
President George W. Bush pulled out of Kyoto in 2001, saying it would cost U.S. jobs and wrongly excluded developing nations from an overall goal of cutting industrialized nations' emissions by 5.2 percent below 1990 levels by 2008-12.
U.S. emissions of greenhouse gases, released mainly by burning fossil fuels, were about 16 percent above 1990 levels in 2004. But Kyoto signatories Spain, Portugal, Greece, Ireland and Canada are all doing even worse.
NOT ON TRACK
"Countries are not on track to reach even their modest Kyoto targets, despite growing recognition that we are already facing dramatic consequences as a result of climate change," said Catherine Pearce at environmental group Friends of the Earth.
Washington agreed at U.N. talks in Montreal, Canada, in December to take part in a non-binding world dialogue about new ways to combat climate change. And Kyoto's backers agreed to talks about what to do after a first period runs out in 2012.
The U.N. climate change office said this week that Kyoto nations were on target to cut emissions by 3.5 percent compared with 1990 levels by 2012 and could reach the 5.2 percent goal by introducing extra measures.
On Thursday, the British Environmental Agency released a report saying decisions in the next 25 years would be critical.
"We are running out of road on decision making -- unless we dramatically change the use of fossil fuels we will be committing future generations to the most severe impacts of climate change," said Barbara Young, head of the agency.
By 3000, it said historically chilly Britain could resemble the tropics. Seas could be 11.4 meters higher due to melting polar ice, swamping cities like London.
After snubbing Kyoto, Bush has stressed promoting new technologies, such as wind and solar power, to break what he has called a U.S. addiction to oil.
Some experts say Bush's plan lacks a spur to force industry to cut down and say that markets for trading carbon dioxide, the main greenhouse gas, are the best way to encourage cuts.
In the European Union, carbon dioxide in a market for industrial pollution allowances traded at 26.9 euros ($31.96) per tonne, reflecting growing belief in the scheme, and up from about 7 euros a year ago.