By Alex Kirby
BBC News Online environment correspondent
The UK Government has unveiled plans for a switch towards cleaner forms of energy, and away from fossil fuels and nuclear power.
The government wants to focus on renewable energy
The long-awaited Energy White Paper, published on Monday, spells out plans for radically cutting the pollution blamed for global warming.
It proposes reducing the amount of carbon dioxide (CO2) released into the atmosphere to 60% of 1990 levels by about 2050.
It also announces the running-down of nuclear power stations, which currently supply about 25% of UK electricity.
Instead, the White Paper encourages renewable power, such as wind and wave energy, and energy efficiency.
These, it says, "will have to achieve far more in the next 20 years than previously. We believe such ambitious progress is achievable, but uncertain."
It says the government will aim to go far beyond its stated goal that 10% of electricity should come from renewables by 2010 - up from 3% now.
"We now set the ambition of doubling renewables' share of electricity generation in the decade after that", it says.
Measures to cut down on the amount of energy actually used, or wasted, are also proposed.
The Prime Minister, Tony Blair, is using a rare speech on the environment to commit the UK to the ambitious energy goals.
The Energy Minister, Brian Wilson, told the BBC the White Paper signalled "a good day" for the environment, although the UK would have to strive to meet its targets.
ENERGY PAPER'S MAIN POINTS
CO2 emissions to be cut drastically
No new nuclear power stations to be built for present
More electricity to come from clean sources like waves and wind
New moves to cut energy use and waste
He said: "We have a firm existing target for renewables to make up 10% of electricity in the UK by 2010 and we say we should be aiming to double that by 2020.
"Ten per cent by 2010 is a challenging target."
But some analysts doubt whether targets, particularly those on CO2, can be achieved without nuclear energy.
Britain's 16 nuclear power stations will all reach the end of their working lives in about 30 years, and the White Paper does not back the building of any more at present. But it keeps its options open.
It says: "We do not rule out the possibility that at some point in the future new nuclear build might be necessary if we are to meet our carbon targets."
The Trade and Industry Secretary, Patricia Hewitt, told BBC Radio 4's Today programme a major new nuclear programme would have undermined the drive for efficiency and renewables.
But she added: "We are not absolutely ruling out new nuclear build
'No actual targets'
Environmental groups have welcomed the move away from nuclear power.
Friends of the Earth said: "The White Paper will hopefully sound the final death knell for nuclear power in Britain".
Some householders as well as the nuclear industry may be disgruntled by the proposals, which will add to electricity prices.
LIKELY EFFECT ON ENERGY BILLS BY 2020
Household bills up 5-15%
Industrial electricity prices to rise by up to 25%
Industrial gas prices to rise by up to 30%
The paper says the new policies will add between five and 15% to household electricity prices, up to 25% to industrial electricity prices and up to 30% to industrial gas prices by 2020.
It has already been derided as "incompetent, irrelevant and frankly dangerous" by Sir Bernard Ingham, secretary of the Supporters of Nuclear Energy group.
"At a time when greenhouse emissions are rising in Britain, it proposes to continue to allow the nuclear industry, which emits no greenhouse gases, to run down," he said.
By 2010 the UK is on course to be a net fuel importer, for the first time since the industrial revolution.
By 2020, the White Paper says, imported energy could be supplying three-quarters of the UK's needs. It says coal is still important for generating power.
There will be more research into ways of storing CO2 where it cannot affect the climate, probably deep underground.
But it does not tackle aircraft carbon emissions, which are a rapidly rising proportion of total emissions.
Nor does it say much about land transport, which in the UK will soon emit more CO2 than electricity generation.