The Royal Society has urged the government to show "political courage" in its forthcoming White Paper on energy, and make a clear decision on the future of nuclear power.
Without nuclear energy, Britain would have to rely increasingly on fossil fuels, leading to increasing carbon dioxide emissions and the catastrophic consequences of global warming, it said
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The White Paper must demonstrate joined-up thinking on how to ensure a secure supply of affordable energy
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Royal Society
Britain currently gets about a quarter of its energy from nuclear power, but its 16 stations will reach the end of their working lives in about 30 years, and there is a moratorium on building new ones.
The warning came in a joint statement from the Royal Society's president, Lord May of Oxford, and vice-presidents Professors David Wallace, Patrick Bateson, John Enderby, and Julia Higgins.
"In the short to medium term, it is difficult to see how we can reduce our dependence on fossil fuels without the help of nuclear power," they said.
The scientists said growth in renewable energies such as wind, wave, and solar power would not be fast enough to make up for the loss of capacity resulting from a phasing-out of nuclear power.
As it is, they said, the UK's carbon dioxide emissions have risen over the past two years.
Ministers divided
Professor Wallace told the BBC he would be delighted if renewable energy could make up for the nuclear shortfall in coming years.
"But that's a big if. We would need something like 20,000 wind turbines.... they'd form a line shoulder to shoulder right across the length of Britain."
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In the short to medium term, it is difficult to see how we can reduce our dependence on fossil fuels without the help of nuclear power
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Royal Society
The Royal Society has long campaigned for the building of new power plants, said BBC science correspondent Pallab Ghosh.
But ministers are divided on whether to give a green light to more nuclear plants.
The Royal Society suspects the government will duck the issue in its White Paper, and put off the decision until after the next election.
But that, said the scientists, would close the options for the nuclear industry - with no new nuclear power stations operating in the UK within the next 15 years.
By then, Britain's nuclear capacity would have been halved, they said.
They urged the government to take a stand in the White Paper and explain clearly to the public "how nuclear power, renewables and energy efficiency measures could best contribute to a future in which carbon dioxide emissions are drastically reduced".
Greenpeace, which has long been opposed to nuclear power, said the government could make up the energy shortfall with renewables if it put its mind to it.
The group's director Steven Tindale told the BBC: "There's plenty of renewable resource out there. It only becomes ambitious if the government fails to make the investment in terms of public subsidy and fails to support renewables through planning guidance.
"And the idea that building new nuclear power stations wouldn't require large amounts of public subsidy and a massing amount of tinkering with he planning system is a bit fanciful."
The White Paper is due to be published in the coming weeks.