The world can no longer avoid dangerous global warming because countries have done little to tackle the problem apart from spout “rhetoric”, a leading economist has warned.

Professor William Nordhaus, of Yale University in the US, said it was no longer practicably feasible to keep the level of warming to within two degrees Celsius above pre-industrial levels, the point at which climatologists believe the world will start to experience particularly dangerous climate change.

This would see devastating storms, droughts, deadly heat waves and floods all become significantly more common, making some areas of the planet increasingly difficult for humans to inhabit.

The US military, among others, has expressed concern about the security implications of the mass movements of people that such scenarios would likely bring about.

Professor Nordhaus, a noted expert on the economics of climate change, wrote in a paper called Projections and Uncertainties About Climate Change in an Era of Minimal Climate Policies: “The international target for climate change with a limit of 2C appears to be infeasible with reasonably accessible technologies.

“And this is the case even with very stringent and unrealistically ambitious abatement strategies.

“This is so because of the inertia of the climate system, of rapid projected economic growth in the near term, and of revisions in several elements of the model.

“A target of 2.5C is technically feasible but would require extreme virtually universal global policy measures.”

He said in all the world only the European Union had introduced major policies designed to reduce global warming – but was scathing about what those would actually achieve.

“Notwithstanding what may be called ‘The Rhetoric of Nations’, there has been little progress in taking strong policy measures,” Professor Nordhaus wrote.

“For example, of the six largest countries or regions, only the EU has implemented national climate policies, and the policies of the EU today are very modest.

“Moreover, from the perspective of political economy in different countries as of December 2016, the prospects of strong policy measures appear to be dimming rather than brightening.”

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However Professor Richard Betts, head of climate impacts research at the Met Office’s Hadley Centre, said Professor Nordhaus’s analysis did not mean the world should give up.

A key factor in predictions of temperature rise is the sensitivity of the atmosphere to further emissions of greenhouse gases.

And Professor Betts wrote in an email: “The economics side is outside of my expertise, but on the climate side, I see that Nordhaus's model assumes a climate sensitivity (the warming due to doubling CO2) near the middle of the range of estimates.

“The IPCC [Intergovernmental Panel on Climate Change] range of estimates climate sensitivity is actually quite wide, so if it turns out that the sensitivity is in the lower half of the IPCC range then that would make 2C more feasible than Nordhaus suggests on the basis of his economic analysis.

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“In any case, even if 2C does turn out to be unavoidable, this does not mean that we should give up hope – it would still make sense to try to avoid even higher levels of warming.”

The Paris Agreement on climate change suggested that allowing 2C of warming might not be good enough to avoid serious problems for humanity and adopted the ambition of restricting it to as close to 1.5C as possible.

However temperatures have already risen by nearly 1C, making a 1.5C target extremely optimistic.

Professor Nordhaus's warning is the latest in a series from scientists that time is running out to address climate change.

In January last year, some of the world's leading scientists warned in a joint letter to The Independent that the much-lauded Paris Agreement was far too weak and offered only "false hope".

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One study published in September predicted that the world could hit 2C of warming as early as 2050 as the atmosphere was heating up "much faster" than expected.

And another in November suggested the earth could actually become more sensitive to greenhouse gases as it gets warmer, so much so that average temperatures could potentially rise by more than 7C by 2100.

At the time, the leading climatologist Professor Michael Mann told The Independent that if the atmosphere was truly as sensitive as that then it would be "game over" for efforts to prevent dangerous global warming.

Commenting on Professor Nordhaus’s paper, Professor Mann, who also cautioned that he was not an economist, said that restricting warming to 2C was “already a real challenge” – something he has written about previously.

However he added: “I think it is an overstatement to say (as Nordhaus does in the abstract) that ‘it will be extremely difficult to achieve the 2C target of international agreements even if ambitious policies are introduced in the near term’.

“The Paris Agreement has put us on a pathway that can get us there given a ratcheting up of the commitments already made by the nations of the word.

“Physics isn't an obstacle, only willpower is, at this point. I'm wary of economists’ assumptions about our willpower to take dramatic actions when necessary.

“A similar argument to Nordhaus might have been used to argue we couldn't possibly mount the mobilisation necessary to win World War II. But we did.