Liberal Democrats have voted to support the building of a new generation of nuclear power plants - a policy U-turn which marks an important victory for the Party's leadership.
Party members at the Glasgow conference voted 230 to 183 to support nuclear power in "limited" circumstances.
Climate Change Secretary Ed Davey earlier warned the Party not backing nuclear would be "reckless".
He said he had changed his mind because of climate change.
The motion also backed continued operations at existing nuclear power stations until the end of their working lives.
Delegates also voted to support fracking - but with an amendment to ensure that pollution levels were properly monitored and residents living close to fracking sites were properly consulted about plans.
Mr Davey said climate change posed a real and massive danger to the planet and warned Liberal Democrats the party would look reckless if they ruled out nuclear - a "genuinely low carbon source of electricity" - as an option.
There were concerns about the cost of new nuclear power stations but Mr Davey told the conference he would not allow the price of projects to get out of control.
Campaigners had urged Lib Dems to reject the motion, ahead of the vote calling it a "crunch day" for the party.
Craig Bennett, of Friends of the Earth, said the Lib Dem backing of nuclear power had punched "a huge hole in the Liberal Democrats' fast-sinking green credibility".
"Nuclear power comes with massive costs attached. Ed Davey is deluded if he thinks new reactors can go ahead without public subsidy - building them will result in the Liberal Democrats, yet again, breaking their promises.
"Championing a plastic bag charge is a drop in the ocean. With its support for new reactors and gas-fired power stations and refusal to back power sector decarbonisation the Liberal Democrats are fast becoming Tory-lite when it comes to the environment."
But Mr Davey told delegates: "When I have listened to pro-nuclear Liberal Democrats over the years, there is one argument I have found increasingly difficult to answer and that is the climate change argument.
"We are going to need vast amounts of low-carbon electricity to tackle climate change. Why? Because if our carbon capture and storage plans don't work, we may have to replace all fossil fuels for electricity generation, that is about 60% of all generation.
"If we do that without nuclear, you will need to replace about 85% of electricity generation. That's huge."
Mr Davey said he was absolutely determined not to sign any contract for new nuclear power stations which relied on public subsidy, adding: "New nuclear must be cost-competitive. We will not repeat the history of mistakes on nuclear."
He also announced a new cash incentive to build more wind turbines on the Scottish islands, including Shetland, Orkney and the Western Isles.
He told delegates that the "huge wind potential" of Scotland's Islands had been well known but that other parties had done nothing about it.
He said he hoped the draft deal, which would be worth £115 per mega watt hour (MWh) for onshore wind, would help harness the "amazing green energy sources" on the islands.
It could lead to hundreds more turbines generating an additional 400 MWh for the grid.
Mr Davey's speech comes a day after Deputy Prime Minister Nick Clegg unveiled plans to charge 5p for plastic bags in England in a bid to discourage their use.
The charge, which will only apply to supermarkets and larger stores, will begin after the 2015 election, with the proceeds going to charities.