There is a great deal of agreement on the Fabian/FEPS panel about the Copenhagen deal, among those who want a deal which matches the science of climate change. But the question of political barriers and constrains are opening up some differences of strategies for change.
And Ken Livingstone is having to take up the role of political realist.
Andy Atkins of Friends of the Earth and Keith Allott of WWF have stressed the need for the science to be paramount: "You can't change the science. It is non-negotiable. You can change the political constraints. That's the point: that's what politics is for", Allott has said.
To which Livingstone has responded>
"There is no disagreement of principle between us. I agree we could stabilise the climate below two degrees [global average temperature change]. If I was Emperor of the world tomorrow we would do so. [Laughter]"
But he is looking at the politics of the US Senate and the interests involved in the environment committee:
"So I think, in reality, we will end up closer to four degrees than two degrees".
"So I think it is going to be very hairy. It is going to be catastrophic. But there will still be human civilisation recognisable at the end of the century - and if we don't make that deal there won't be".