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Global Warming IS REAL, argues sceptic mathematician - it just isn't THERMAGEDDON

IPCC hid the good news? Let's find out

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Interview The "certainty" that underpins European and UK climate policy may be wildly misplaced, as the models that the climate science establishment presents to politicians as evidence run far too hot.

That's according to a report released yesterday by UK think-tank the Global Warming Policy Foundation.

And this is very good news, says the report's author, Nicholas Lewis. Lewis is a relative newcomer to climate science who published his first peer-reviewed paper in 2011. Lewis also submitted written evidence published in the IPCC's Fifth assessment Report, AR5.

Lewis doesn't disagree that CO2 contributes to global warming - and most of the additional CO2 is caused by humans. The science today, however, shows around half a degree of surface temperature warming manifesting itself over the next 70 years. This the most important climate discovery in recent years - and you may reasonably think it should have grabbed the headlines.

However, with politicians pleading to be told what to do by scientists, the IPCC process - dominated by bureaucrats and politicians - pulled its punches. It acknowledged the finding but only referred to the lowering obliquely, and didn't explain why its own estimates had been lowered. It omitted to make a "best guess" at all - unlike in previous blockbusters.

We spoke to Lewis this week to unravel the mystery, and explain his workings after the publication of his review of the AR5's physics assessment yesterday (PDF). Lewis's subject is climate sensitivity - the response of the system to increasing amounts of greenhouse gas forcings - and this is the kernel upon which climate science is based. Lewis studied maths and physics at Cambridge and his career included modelling: he's an expert on the uses and misuses of Bayesian mathematics.

Lewis also told us he'd already found schoolboy maths error in the IPCC's AR4 published in 2007.

Known knowns and unknowns

The core of climate estimates is two key figures in the basic physics: equilibrium climate sensitivity (ECS) and the transient climate response (TCR, a figure derived from ECS). Climate sensitivity is the response of the system to a doubling of a forcing, by the time it reaches equilibrium. TCR is a more useful figure since it shows the response over a shorter time frame. Once the latest observational evidence is incorporated, these are lower than previously guessed.

"It's slightly counter-intuitive," Lewis agrees. "Because of a better understanding of aerosols we think they play less of a role in the climate. So in a period where the temperature hasn't really changed, the influence CO2 must be less than thought."

As he explains in his latest review:

The observed temperature increase to date could result from a high climate sensitivity combined with a large aerosol cooling effect, or a low sensitivity combined with a small aerosol cooling effect (or combinations in between these extremes). Therefore, to the extent that aerosol forcing is small, sensitivity to carbon dioxide concentrations must also be relatively low.

AR5 uses a combination of simulations and satellite observations to derive its aerosol forcing estimate. But satellite observations, Lewis adds, put aerosols even lower.

(Before you read on, bear in mind there are two related avenues of enquiry thrust at policy-makers. There are workings based on an energy budget model, and there are the models. Budget calculations are generally lower than the runaway models. Lewis's best estimate ECS is 1.7˚C, close to the IPCC's lower bound of 1.5˚C, but much lower than the models average of 3.2˚C [and best estimate of 2.9˚C]. For TCR his best estimate is 1.3˚C, again close to the IPCC's lower bound of 1 and much lower than the GCMs.)

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