Overnight, more than 40 national nuclear societies from around the world have signed a Nuclear for Climate declaration.

Meeting at the 2015 International Congress on Advances in Nuclear Power Plants in Nice, France, the declaration commits the nuclear societies to limiting global warming to two degrees by 2050.

That's thought by many to be a 'safe' level of climate change, and is the goal that will be on the table at Paris later this year at the UN climate talks, as nations seek agreement on a new post-2020 global climate treaty.

But top US climate scientist James Hansen says the goal is a 'nonsense', and the world is on the wrong track thinking that two degrees of warming is 'safe'.