Mere mention of the Paris climate talks is enough to make James Hansengrumpy. The former Nasa scientist, considered the father of global awareness of climate change, is a soft-spoken, almost diffident Iowan. But when he talks about the gathering of nearly 200 nations, his demeanour changes.

“It’s a fraud really, a fake,” he says, rubbing his head. “It’s just bullshit for them to say:…