By Gareth Jones
Business Editor, BBC Wales
Leading environmentalists at the Hay Festival have told audiences that if we do not alter how we generate electricity very soon, the world faces a change in climate so destructive that civilization itself will be threatened.
Wylfa nuclear power station is due to close in four years time
But there was disagreement over exactly how we in Wales should respond.
The Welsh Assembly Government (WAG) favours a combination of renewable energy sources, mainly from the wind and the tides, together with clean coal technology and gas.
It has ruled out a return to nuclear power.
It says this approach should help Wales to meet its targets to reduce emissions of carbon dioxide, one of the gases blamed for increasing the threat of damaging climate change.
Professor Lovelock said nuclear power was criticised 'to absurdity'
However, one of the environment movement's most influential thinkers, James Lovelock, says this simply will be not be enough.
In his book The Revenge of Gaia, the scientist says we must take drastic action now -and that includes building many more nuclear power stations.
He told BBC Wales he thought opponents of nuclear exaggerated the problem of waste.
'It's been hyped to the point of absurdity. It's not a big danger unless you go and sit on it."
"The trouble with a nuclear revival," says Jonathon Porritt, who was talking about his book Capitalism as if the World Matters, "is that it would 'take money and effort away from other options like renewables, small-scale generation and energy efficiency".
With many environmentalists against nuclear power, what future for coal - an energy source that lies in abundance under Welsh soil?
"Attempts to find ways of burning coal cleanly are entirely legitimate," Porritt told me.
"But we shouldn't underestimate the cost of capturing and storing carbon dioxide from coal-fired power stations."
There was outright opposition to a UK coal revival from Dr Jeremy Leggett, author of Half Gone, a book claiming that oil will run out much faster than most people think.
Dr Leggett also runs the UK's largest solar electricity company.
"The big battle coming up will be between coalification and solarisation," he said.
"Between those who believe, like me, that the sun, wind and tides are the best way to generate energy, and those who favour a massive retreat into coal. But why bother with unproven methods when renewable technology is ready to go?"
There was criticism of WAG's energy policy from Porritt.
"There's been a lot of talk about new energy sources from Welsh ministers, but not about saving energy. We need to manage demand much more."
On such a complex issue, views are bound to differ.
But none of the top environmentalists appearing at Hay this week disagreed on this central point - that anything we do on energy will have its drawbacks, but that these major decisions cannot be put off any longer.