Nearly 200 nations gathered in Paris for the COP 21 Climate Change Summit where the first deal to commit to cutting emissions was reached after two weeks of tense negotiations-a sign of environmental progress for the world, but scientist James Hansen seems disagrees.  

The former Nasa scientist, considered the father of global awareness of climate change, says, "It's a fraud really, a fake", reports The Guardian.

"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.

Hansen, 74, has just returned from Paris where he again called for a price to be placed on each tonne of carbon from major emitters (he's suggested a "fee" – because "taxes scare people off" – of $15 a tonne that would rise $10 a year and bring in $600bn in the US alone). There aren't many takers, even among "big green" as Hansen labels environment groups.

Hansen has been a nagging yet respected voice on climate change since he shot to prominence in the summer of 1988. The Nasa scientists, who had been analyzing changes in the Earth's climate since the 1970s, told a congressional committee that something called the "greenhouse effect" where heat-trapped gases are released into the atmosphere was causing global warming with a 99% certainty.

From being possibly America's most celebrated scientist, Hansen is now probably its most prominent climate activist. He's been arrested several times in protests outside the White House over mining and the controversial Keystone pipeline extension.

In One particular paper, Hansen and 16 colleagues found that Earth's huge ice sheets, such as those found in Greenland, are melting faster than expected, meaning that even the 2C warming limit is "highly dangerous".

The sea level could soon be up to five meters higher than it is today by the latter part of this century, unless greenhouse gases aren't radically slashed, the paper states. This would inundate many of the world's cities, including London, New York, Miami and Shanghai.

"More than half of the world's cities of the world are at risk," Hansen says. "If you talk to glaciologists privately they will tell you they are very concerned we are locking in much more significant sea level rises than the ice sheet models are telling us.

"The economic cost of a business as usual approach to emissions is incalculable. It will become questionable whether global governance will break down. You're talking about hundreds of million of climate refugees from places such as Pakistan and China. We just can't let that happen. Civilization was set up and developed with a stable, constant coastline."

There is a positive note to end on, however. Global emissions have somewhat stalled and Hansen believes China, the world's largest emitter, will now step up to provide the leadership lacking from the US. A submerged Fifth Avenue and deadly heatwaves aren't an inevitability.

"I think we will get there because China is rational," Hansen says. "Their leaders are mostly trained in engineering and such things, they don't deny climate change and they have a huge incentive, which is air pollution. It's so bad in their cities they need to move to clean energies. They realise it's not a hoax. But they will need co-operation."