A leading climate scientist has denounced the Paris climate change agreement as a “fraud” - saying there is "no action, just promises”.

Professor James Hansen - credited as being the “father of climate change awareness” - told the Guardian the talks that culminated in a deal on Saturday were just “worthless words”.

Speaking as the final draft of the deal was published on Saturday afternoon, he said: “It’s just b******t 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 agreement - which still has to be ratified by the 196 countries who took part in the talks - laid out a pledge to limit the average rise in global temperatures to “well below” 2C above pre-industrial levels.

This is higher than the 1.5C rise campaigned for by a coalition of at risk Pacific Island countries - most notably the Marshall Islands in Micronesia - who say they need the lower limit in order to “stay alive”.

The agreement outlines an aim of reducing temperatures to a 1.5C - but does not commit to it.

Paris climate talks in pictures Show all 12 1 /12 Paris climate talks in pictures Paris climate talks in pictures A man is covered with a multi-coloured banner with the message, "Climate" as environmentalists attend a demonstration near the Eiffel Tower in Paris, France, during the World Climate Change Conference 2015 (COP21) that meets in Le Bourget, December 12, 2015 Reuters Paris climate talks in pictures French President Francois Hollande (C) and French Foreign Minister Laurent Fabius (R) applaud after a statement at the COP21 Climate Conference in Le Bourget, north of Paris, on December 12, 2015. The years-long quest for a universal pact to avert catastrophic climate change neared the finish line today with conference host France announcing that the final draft had been completed in the early hours of the morning. Getty Paris climate talks in pictures US Secretary of State John Kerry (C) speaks with China's Special Representative on Climate Change Xie Zhenhua (R) and officials at the COP21 Climate Conference in Le Bourget, north of Paris, on December 12, 2015. The years-long quest for a universal pact to avert catastrophic climate change neared the finish line today with conference host France announcing that the final draft had been completed in the early hours of the morning. Getty Paris climate talks in pictures Delegates and members of NGO's read and work on copies of 'The adoption of the Paris agreement' is pictured after the announcement of the final draft by French Foreign Affairs minister Laurent Fabius at the COP21 Climate Conference in Le Bourget, north of Paris, on December 12, 2015. The years-long quest for a universal pact to avert catastrophic climate change neared the finish line with conference host France announcing that the final draft had been completed in the early hours of the morning Getty Paris climate talks in pictures UN climate chief Christiana Figueres (C) speaks with French President Francois Hollande (L), United Nations Secretary General Ban Ki-moon (2ndL) and French Foreign Minister Laurent Fabius (R) after a statement at the COP21 Climate Conference in Le Bourget, north of Paris, on December 12, 2015. The years-long quest for a universal pact to avert catastrophic climate change neared the finish line today with conference host France announcing that the final draft had been completed in the early hours of the morning Getty Paris climate talks in pictures A Swiss Dominican priest poses with activists dressed as polar bears as activists gather for a demonstration to form a giant red line at the Avenue de la Grande armee boulevard in Paris on December 12, 2015, as a proposed 195-nation accord to curb emissions of the heat-trapping gases that threaten to wreak havoc on Earth's climate system is to be presented at the United Nations conference on climate change COP21 in Le Bourget, on the outskirts of Paris. Getty Paris climate talks in pictures Activists hold up a giant banner reading 'Climate justice' by association 'ourpowercampaign' during a demonstration near the Arc de Triomphe at the Avenue de la Grande armee boulevard in Paris on December 12, 2015, as a proposed 195-nation accord to curb emissions of the heat-trapping gases that threaten to wreak havoc on Earth's climate system is to be presented at the United Nations conference on climate change COP21 in Le Bourget, on the outskirts of Paris. Getty Paris climate talks in pictures Representatives of indigenous peoples demonstrate in Paris, France, as the World Climate Change Conference 2015 (COP21) continues at Le Bourget, December 12, 2015. Reuters Paris climate talks in pictures Environmentalists demonstrate near the Arc de Triomphe in Paris, France, as the World Climate Change Conference 2015 (COP21) continues at Le Bourget, December 12, 2015. Reuters Paris climate talks in pictures Environmentalists demonstrate near the Arc de Triomphe in Paris, France, as the World Climate Change Conference 2015 (COP21) continues at Le Bourget, December 12, 2015. Reuters Paris climate talks in pictures Activists form a giant red line during a demonstration on the Avenue de la Grande armee boulevard in Paris on December 12, 2015, as a proposed 195-nation accord to curb emissions of the heat-trapping gases that threaten to wreak havoc on Earth's climate system is to be presented at the United Nations conference on climate change COP21 in Le Bourget, on the outskirts of Paris ALAIN JOCARD/AFP/Getty Images Paris climate talks in pictures The slogan "No Plan B" is projected on the Eiffel Tower as part of the World Climate Change Conference 2015 (COP21) in Paris, France, December 11, 2015. Reuters

Professor Hansen said the decision is meaningless without a commitment to tax greenhouse emissions - which he believes is the only way to reduce emissions fast enough.

He said: “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.”

It comes as President Barack Obama hailed the agreement as "the best chance we have to save the one planet we have".

Speaking hours after the deal was signed he said it was a "turning point" in history and a defining moment for his administration.