By Alex Kirby
BBC News Online environment correspondent
The UK is to make swingeing cuts in emissions of gases thought to cause climate change, the government says.
Coal use has crept up recently
The Environment Secretary, Margaret Beckett, held out the prospect of a 60% cut in carbon dioxide emissions by 2050.
The UK has already made deeper cuts in six gases than it promised to achieve.
But emissions by the US are projected to rise massively on present trends.
Mrs Beckett was speaking at the launch of a United Nations report on the UK's performance in cutting emissions.
The report, by the UN's Framework Convention on Climate Change (UNFCCC), said the UK had reduced its greenhouse gases by 12.8% between 1990 and 2000, successfully uncoupling economic growth from energy and emissions intensity.
Onward and upward
Under the Kyoto Protocol, the international agreement on tackling climate change, the UK is committed to cuts of 12.5% in the 1990 levels of the six main greenhouse gases by between 2008 and 2012.
The government has also promised to cut emissions of carbon dioxide (CO2), the main greenhouse gas produced by human activities, to 20% below 1990 levels by 2010.
Road traffic is rising
Mrs Beckett said: "We have made significant reductions in emissions and now aim to go much further to get us on the path of a 60% cut in CO2 emissions by 2050.
"And on the path to that, we remain committed to our domestic goal of carbon emissions going down by 20% by 2010."
Many scientists say CO2 cuts of about 60% by mid-century will be needed to reduce the human impact on the climate to tolerable levels.
A government advisory body, the Sustainable Development Commission, said in February it thought the UK would "fall well short" of cutting CO2 by 20% by 2010.
The commission, which is chaired by the environmental campaigner Jonathon Porritt, said: "The UK is unlikely to achieve even two-thirds of that reduction, and maybe less than half."
Huge rise ahead
The UNFCCC says the UK has "succeeded remarkably" in cutting emissions by 12.8% already, and has made "commendable progress".
But it released projections for the probable emissions by 2010, on present trends, by 30 Kyoto signatories.
Nuclear power's future remains "uncertain"
Only 12, it says, look likely to achieve cuts. Those projected to record increases include the US, likely as things stand to be emitting 32.4% more of the six gases.
The US produces about a quarter of the world's greenhouse emissions. Two years ago it said it would not ratify the Kyoto Protocol.
But both Mrs Beckett and UNFCCC officials said the US was a loyal and active supporter of the convention, and was taking steps outside the protocol to reduce its emissions.
The report said the UK still faced challenges in addressing climate change, including the role of renewable energy, the "uncertain future" of nuclear power, and growing emissions from transport.
Friends of the Earth said the government should not be complacent. It said: "Department for Transport statistics show car traffic levels on Britain's roads were 3% higher in 2002 than in 2001.
"Emission increases caused by growing air travel are not included in the UN's assessment, and cuts in emissions from the 'dash for gas' in the early 1990s have been partly eroded by the greater use of coal under Labour."
Not enough signatories have yet ratified the Kyoto Protocol for it to enter into force, and it is not certain they ever will.
And critics of climate science continue to insist that human activity is irrelevant, and attempts to moderate our influence therefore misplaced.