Mere mention of the Paris climate talks is enough to make James Hansen grumpy. 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 demeanor changes.

“It’s a fraud really, a fake,” he says, rubbing his head. “It’s just bullshit for them to say: ‘We’ll have a 2C warming target and then try to do a little better every five years.’ It’s just worthless words. There is no action, just promises. As long as fossil fuels appear to be the cheapest fuels out there, they will be continued to be burned.”

The talks, intended to reach a new global deal on cutting carbon emissions beyond 2020, have spent much time and energy on two major issues: whether the world should aim to contain the temperature rise to 1.5C or 2C above preindustrial levels, and how much funding should be doled out by wealthy countries to developing nations that risk being swamped by rising seas and bashed by escalating extreme weather events.

But, according to Hansen, the international jamboree is pointless unless greenhouse gas emissions aren’t taxed across the board. He argues that only this will force down emissions quickly enough to avoid the worst ravages of climate change.