One of Britain’s top climate scientists has launched a blistering attack on actress Emma Thompson and the BBC, accusing them of ‘scaremongering’ over the speed of global warming – and risking a worsening of the refugee crisis.

Richard Betts, head of climate impacts research at the Met Office and a professor at Exeter University, launched his attack on Twitter about an interview Ms Thompson gave to Newsnight presenter Emily Maitlis last Wednesday.

He followed it up with a longer critique – an extract of which this newspaper publishes today – on the website of HELIX, a prestigious EU-wide climate research programme which he also directs.

Actress Emma Thompson (right) warned that if the drilling went ahead, the world would be 4C hotter by 2030

The actress, a Greenpeace activist who that morning had taken part in a protest against Shell’s plans to drill for oil in the Arctic, warned that if the drilling went ahead, the world would be a staggering 4C hotter by 2030.

She said: ‘If they take out of the Earth all the oil they want to take out, if you look at the science, our temperature will rise 4 degrees Celsius by 2030, and that’s not sustainable.’

Ms Maitlis did not challenge her.

In his first tweet, Prof Betts asked: ‘Who briefed Emma Thompson? Clearly not someone who actually knows about climate science.’

He added: ‘Has it occurred to scaremongers like Emma Thompson that exaggerating climate change could drive more migration unnecessarily? Irresponsible.’

Other scientists were equally critical. Dr Ed Hawkins, at Reading University, told this newspaper: ‘Climate change poses substantial risks to humans and ecosystems, but what Emma Thompson said about the timescales of predicted warming was inaccurate.’

In his blog post, Prof Betts points out that the authoritative UN Intergovernmental Panel on Climate Change gives a ‘wide range of estimates of the speed of future warming’ – but none of them is anywhere near 4C by 2030.

He adds that under the highest scenario for future emissions, ‘the earliest time of reaching 4C above pre-industrial was around 2070, and the latest sometime after 2100’.

Ms Thompson hit back yesterday, saying: ‘I’d like to say to him [Richard Betts]: Are you insane, have you been to the Arctic, have you seen the state of the glaciers? I’ve talked to the experts... this is not scaremongering.’

A BBC spokeswoman said: ‘In a longer interview Emily would have pressed Thompson to justify her assertion.’ She refused to say whether the BBC would be correcting Ms Thompson’s statement.

Professor Richard Betts, Met Office head of climate impacts research

She is just crying wolf... It may even make refugee crisis worse

Comment by Professor Richard Betts, Met Office head of climate impacts research

In a recent BBC Newsnight item, the actress Emma Thompson spoke passionately and in no uncertain terms about 4C warming by the year 2030, and stated that ‘in a few years… whole swathes of the Earth will become uninhabitable’.

These statements do not reflect what the science actually says.

Some might argue that the focus should be on worst-case catastrophic scenarios, leaving no room for doubt, in order to promote urgency in emissions cuts.

It’s certainly easy to see why this might be tempting, as global emissions have continued to rise despite clear indications that unchecked climate change poses large risks.

This seems to be the case in Emma Thompson’s recent BBC Newsnight item. Does this matter? What’s the harm in a bit of exaggeration if it’s in a good cause? To my mind, there are three reasons why it’s a problem.

Firstly, making wild predictions that don’t come true obviously harms your credibility. It’s the old ‘boy who cried wolf’ story – he made up the story of the wolf, so when it eventually did come, nobody believed him. There was a wolf, but only later on.

When the world has not become a barren wasteland within a few years, it will be easy for critics to say that the whole climate change problem has been exaggerated.

It has not been exaggerated – at least not by mainstream science – but that will be easily overlooked when harking back to these claims.

Secondly, if people come to believe that catastrophic impacts are only round the corner, this could lead to wrong decisions made in panic.

A lot is being done to make us more resilient to the climate change we’ve already set in motion – new flood defences, plans for reservoirs and water supplies, and so on. But these are expensive, and doing these too early could cost billions. And if people are scared into moving away from their homelands because they think it will be uninhabitable, this would only add to the existing refugee crisis, for no good reason.

Finally, even if the world does make major emissions cuts very soon, this will take time to filter through into tangible effects on global warming. There is already more warming in the pipeline which is unavoidable. Therefore anything projected for the next few years is already unavoidable.

If ‘whole swathes’ really will become uninhabitable ‘in a few years’, then there is absolutely nothing we can do about it, however urgently we cut emissions.

Whether Shell drills for Arctic oil or not, the changes for the next few years are already locked in. Emma Thompson’s apocalyptic vision is therefore one of despair, not something that can credibly be avoided through action, however drastic.

Fortunately, while Ms Thompson’s concerns are valid in the longer term, her timing isn’t supported by the science.

Higher levels of climate change and the associated risks are further off than she fears, and hence could still be avoided.