One of the world’s most eminent climate scientists – for several decades a warmist – has defected to the climate sceptic camp.

Lennart Bengtsson – a Swedish climatologist, meteorologist, former director of the Max Planck Institute for Meteorology in Hamburg and winner, in 2006, of the 51st IMO Prize of the World Meteorological Organization for his pioneering work in numerical weather prediction – is by some margin the most distinguished scientist to change sides.

For most of his career, he has been a prominent member of the warmist establishment, subscribing to all its articles of faith – up to and including the belief that Michael Mann’s Hockey Stick was a scientifically plausible assessment of the relationship between CO2 emissions and global mean temperature.

But this week, he signalled his move to the enemy camp by agreeing to join the advisory council of Britain’s Global Warming Policy Foundation (GWPF), the think tank created by the arch-sceptical former Chancellor Lord Lawson.

Though Bengtsson is trying to play down the significance of his shift – “I have always been a sceptic and I think that is what most scientists really are” he recently told Germany’s Spiegel Online, denying that he had ever been an “alarmist” – his move to the GWPF is a calculated snub to the climate alarmist establishment.

“He’s a big, big player. The biggest by far to change sides,” says the GWPF’s Benny Peiser. “What’s particularly significant is that his speciality is climate modelling – and computer models, as you know, are at the heart of global warming theory. He is the most significant figure to admit, as many modellers are beginning to notice, that there is an increasing discrepancy between what the models predicted and what the real world data is actually telling us.”

In his interview with Spiegel Online, Bengtsson said:

“I have used most of my career to develop models for predicting the weather. I have learned the importance of forecasting validation, i.e. the verification of predictions with respect to what has really happened. So I am a friend of climate forecasts. But the review of model results is important in order to ensure their credibility. It is frustrating that climate science is not able to validate their simulations correctly. The warming of the Earth has been much weaker since the end of the 20th century compared to what climate models show.”

Bengtsson went on to reject another pillar of the warmist faith – the existence of a “consensus.”

I have great respect for the scientific work that goes into the IPCC reports. But I see no need for the endeavour of the IPCC to achieve a consensus. I think it is essential that there are areas of society where a consensus cannot be enforced. Especially in an area like the climate system, which is incompletely understood, a consensus is meaningless.

He believes that policymakers should be much more cautious in making decisions about the long-term future of climate when the facts are still imperfectly understood.

I do not think it makes sense to think for our generation that we will solve the problems of the future – for the simple reason that we do not know future problems. Let us do a thought experiment and go back to May 1914: Let us try from the perspective of that point in time to make an action plan for the next hundred years – it would be pointless!

Lennart’s is just the latest in a series of defections from the climate alarmist camp to the cause of realism.

Others include:

James Lovelock; English scientist; inventor of Gaia Theory; godfather of Green.

Formerly an arch-exponent of man-made climate doom theory, predicting as recently as 2007, that “billions of us will die; few breeding pairs of people that survive will be in Arctic”. Now admits: “The problem is we don’t know what the climate is doing. We thought we did 20 years ago.” Pro-nuclear; mildly pro-fracking; anti-wind farms.

Judith Curry – American climatologist and chair of the School of Earth and Atmospheric Sciences at the Georgia Institute of Technology.

Though still a self-described “luke warmer”, Curry was probably the most senior member of the warmist establishment – up until Bengtsson’s defection – to fraternise with the enemy. This has earned her the badge of honour of being labelled “anti-science” by Michael Mann. In her blog Climate Etc she tries to encourage climate alarmists to show a sense of proportion and admit the limits of their knowledge. Of the National Climate Assessment report, she wrote:

My main conclusion from reading the report is this: the phrase ‘climate change’ is now officially meaningless. The report effectively implies that there is no climate change otherthan what is caused by humans, and that extreme weather events areequivalent to climate change.

Fritz Vahrenholt – German professor; environmental activist; one of the founders of the German green movement; former Environmental Senator of Hamburg.

Vahrenholt’s climate-sceptical bestseller Die Kalte Sonne (translated as The Neglected Sun) sent shock waves through the German green movement. It earned him the title “eco-reactionary” from the left-liberal German media which was appalled at what they saw as his betrayal of the Cause. Vahrenholt argued that the sun – not CO2 – was the most significant driver of climate change; that predictions of man-made climate doom had been overdone; and that science had been corrupted by political indoctrination.

Sigmar Gabriel – German vice-chancellor; ex environment minister; formerly an enthusiast for green energy policy; now admits that Germany’s Energiewende – its transition to renewables – has been pointless and destructive.

George Monbiot – humorist; Guardian scribe; environmental campaigner; scourge of climate sceptics; has since divided the green movement over his removal of the Atomkraft? Nein Danke sticker on the back of his florally-decorated VW Kombi and his decision that nuclear energy is, after all, the way forward. For this crime he is now being harried by green campaigners who are offering a £100 reward to anyone prepared to arrest him for his “crimes against the environment and humanity.”