Some excerpts from the recent Cambridge meetup between Warmist and skeptical scientists



The Downing event was assembled by Alan Howard, an academic rich enough to have a foundation in his name – and it was the first time many climate scientists have ever attended an event with their critics. "Science is not a religion," said Howard, "it must be criticised". Henrik Svensmark, who offered the most compelling alternative to the IPCC orthodoxy, was among those who gave a presentation. The audience was evenly split, and the IPCC orthodox view took up perhaps two thirds of the day.

On the science, there was little disagreement over the basics, such as the physical properties of CO2, but the degree to which it drives the larger climate was greatly disputed, because the larger system remains a mystery. Even the basics of how different clouds affect temperature is guesswork: water vapour feedback may have a slight negative cooling feedback, or it may have a large positive warming feedback. These must be guessed at, or imagined, through models.

In short, the day lined up Phil Jones, oceanographer Andrew Watson, and physicist Mike Lockwood, the latter to argue that the sun couldn't possibly have caused recent warming. He was followed by the most impressive presentation from Henrik Svensmark, whose presentation stood out head and shoulders above anyone else. Why? For two reasons. The correlations he shows are remarkable, and don't need curve fitting, or funky statistical tricks. And he has advanced a mechanism, using empirical science, to explain them. At the other end of the scale, by way of contrast, the Met's principle research scientist John Mitchell told us:

"People underestimate the power of models. Observational evidence is not very useful," adding, "Our approach is not entirely empirical."

Yes, you could say that....

Watson acknowledged many uncertainties before positing that climate sensitivity – a doubling of CO2 over pre-industrial levels – added 2 to 4.5C to global temperature. "This can be wrong – but it's hard to see how it can be a long way wrong," said Watson.

Other scientists disagree, with Lindzen putting sensitivity at 0.7C, which suggests we've had already had the manmade warming we're going to get. Clouds are poorly understood, and more low clouds means cooling.

The audience also challenged evidence of the causal relationship between CO2 and temperatures. Warmer temperatures mean more CO2 is released through outgassing, and the Antarctic ice core record shows temperature rising, then CO2 following closely behind. Watson said that with feedbacks, it was impossible to separate the two as cleanly as critics would like: more CO2 must surely have an amplification effect, he said.

"There is a good reason to believe ... that climate sensitivity is substantially changing the global climate. Such rapid global change is very rare in the earth's history," he concluded.

The telltale signature of greenhouse gas warming should be warming at the surface and in the troposphere, but not the upper stratosphere. It's even been suggested that carbon taxes should reflect the tropospheric temperature anomaly, rather than surface production. But while the models predict such telltale warming, the observational evidence shows it isn't there. More recently it has been cooling. This really shouldn't be happening.

"We can't explain it ... we have wide uncertainty estimates," acknowledged Watson. "Clouds is a very uncertain area." He again stated that CS was in the range of 1.1C-4C – with more no's from the skeptical side of the room.

Solar physicist Mike Lockwood began with an odd observation: "The stewardship of the planet - and lifestyles - would be much easier if [climate change] was all about the sun." It was a rare example of the IPCC academics letting their intellectual prejudices slip out. Our lifestyles are surely up to us, and policies in response to climate change should be decided coolly and rationally, not handed down as instructions from academic priests. People can get carried away with their own importance at times - particularly scientists.

Lockwood's presentation was quite lucid, though – and surprisingly generous to the next speaker Henrik Svensmark.

"I think it's a lovely idea and I do think it happens, actually. It's very clever. But it happens slowly, and we think it happens in clean maritime air. Over land, there are already enough aerosols present for cloud formation".

Lockwood outlined the sun's influence: its irradiance (TSI), obviously the primary factor in climate change, and also changes in its magnetic field, which modulate to varying degrees its UV output, and its effectiveness in shielding us from cosmic rays. In a nutshell, Lockwood believes modulations in total solar irradiance contribute around 0.75W/m 2to temperature changes, but around 5Wm/2 is needed to explain them. He acknowledged that solar activity – like the value of your portfolio – can go up as well as down. Tracking the last 24 sunspot cycles he thinks there's an 8 per cent chance of arriving in a Maunder Minimum – a period of low sunspot activity and colder weather – in the next 40 years. The strongest argument, according to Lockwood, for the sun not being a driver in recent climatic activity is that "it has been going in the wrong direction for 30 years".

Lockwood was asked about the recent Shapiro paper (PDF/380KB), published in peer-reviewed journal Astronomy & Astrophysics, which suggested that solar irradiance was much more important than previously thought. Alexander Shapiro, at the World Radiation Centre in Switzerland, looked at magnetic fields as a proxy for TSI and concludes that historical reconstructions have underestimated both TSI and UV – by a factor of six.

Lockwood didn't think much of it. "It's based on the premise that there are small magnetic fields between the sunspots. There's no doubt that over 30 years the trend was downward."

Plimer was convincing on the long-term geological record.

"I would like to see why 3 per cent anthropogenic CO2 drives climate, and the other 97 per cent doesn't". The official answer is that the 97 per cent of natural CO2 is perfect equilibrium, but the wicked (fossil fuel) 3 per cent tips everything out of balance.

"For people to call me a Climate Change denier is a demonstration of public ignorance – geology is all about change – it's the science of climate change," he said.

Mitchell's contribution was a mixture of the sophisticated and the simple. He rebutted the idea that you could not model a chaotic system and come out with anything useful. Obviously there's plenty of maths that begs to differ, and Mitchell mentioned some of it, such as Lorenz. Other arguments were odd: Mitchell used the examples of Mars and Venus – two planets which don't have biospheres. This example may prove that there's a greenhouse gas effect – but not much else. And it wasn't seriously in doubt.

So the disagreements really break down into two. There's the science: human influence is either significant or not so significant; and there's economics: we must have policies which make drastic changes to society, lifestyles and industrial policy – what George Monbiot called "a war against ourselves" – or we must sensibly adapt, and are foolish to create more unnecessary human poverty and misery when we don't need to.

This isn't so surprising, really. The most passionate believers in the view that man is irreparably changing the climate are the people with the long lists of radical remedies already prepared; their politics needs the catastrophe, for nobody would entertain their politics for a moment – it wouldn't be mainstream – if it didn't come with a catastrophe attached. Take away the catastrophe, and their politics collapses like a house of cards. Politically we're in a sort of limbo: a few countries have pledged themselves to the course of radically changing lifestyles and industrial policy – but the price of implementing them is political suicide. Things meander along without resolution.

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