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Sabato, 03 Gennaio 2015 00:00

Just how reliable is the IPCC AR5 advice to policy makers? Physics Dr. Clive Best In evidenza

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AR5 Attribution Studies


Just how reliable is the IPCC AR5 advice to policy makers?

The recent IPCC report stated that climate scientists are 95-100% certain that the observed temperature rise since 1850 is anthropogenic. The headline attribution statement in Chapter 10 was

“It is extremely likely that human activities caused more than half of the observed increase in GMST from 1951 to 2010.The best estimate of the human-induced contribution to warming is similar to the observed warming over this period.”

World political leaders are basing policy on the validity of this statement, which is entirely based on comparing CMIP5 models to global surface temperature data. These ‘fingerprinting’ studies are described in chapter 10, which I find all but impossible to comprehend. The underlying assumption in AR5  is that natural climate variability has essentially played no role in warming since 1950. However is this actually true ?

Figure 1 shows a comparison between the ensemble of CMIP5 models and observations.

Agreement until 2000 would appear to be reasonably good. However we then read in Chapter 9 Box 9.1 that in reality:

Model tuning aims to match observed climate system behaviour and so is connected to judgements as to what constitutes a skilful representation of the Earth’s climate. For instance, maintaining the global mean top of the atmosphere (TOA) energy balance in a simulation of pre-industrial climate is essential to prevent the climate system from drifting to an unrealistic state. The models used in this report almost universally contain adjustments to parameters in their treatment of clouds to fulfil this important constraint of the climate system.

So the models are tuned so as to describe past observations. Furthermore periods of cooling are explained by volcanoes which are simulated by something called ‘EMICS’ – Earth System Models of Intermediate Complexity up until 2005. Please don’t ask me what EMICS are but there is also no doubt in my mind that these are also tuned so that  aerosols can then match the global temperature response to volcanic erruptions such as  Pinatubu!

Science of Doom has written a detailed analysis of AR5 attribution studies and even he is not convinced.  He writes:


Chapter 10 of the IPCC report fails to highlight the important assumptions in the attribution studies. Chapter 9 of the IPCC report has a section on centennial/millennial natural variability with a “high confidence” conclusion that comes with little evidence and appears to be based on a cursory comparison of the spectral results of the last 1,000 years proxy results with the CMIP5 modeling studies.


He proposes an alternative summary for Chapter 10 of AR5:>>>>>>>



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