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The IPCC AR5 – First impressions

By , Wed, 2013-10-02 23:11

The IPCC summary for policy makers is out, and as I started writing these lines so was the last draft of the main report. Of course, it will take a while to digest the 2200 pages of the full report (it has a lot of starch!). Until I do, here are my first impressions from having read the summary and having skimmed the full scientific report.

My main conclusion is that this report is to a large extent a rehash of the AR4 report. However, given the lack of any new evidence pointing to humans and the increasing discrepancy between the alarmist models and predictions, the IPCC authors are bluntly making more ridiculous claims as they attempt to fill in the gap between their models and reality.

One of the statements which wonderfully exemplifies the absurdity of the new report is this paragraph discussing the climate sensitivity in the summary for policy makers. They write:

“The equilibrium climate sensitivity quantifies the response of the climate system to constant radiative forcing on multi-century time scales. It is defined as the change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric CO2 concentration. Equilibrium climate sensitivity is likely in the range 1.5°C to 4.5°C (high confidence), extremely unlikely less than 1°C (high confidence), and very unlikely greater than 6°C (medium confidence) 16. The lower temperature limit of the assessed likely range is thus less than the 2°C in the AR4, but the upper limit is the same. This assessment reflects improved understanding, the extended temperature record in the atmosphere and ocean, and new estimates of radiative forcing.”

Now, have you noticed something strange? According to the AR4 report, the “likely equilibrium range of sensitivity” was 2.0 to 4.5°C per CO2 doubling. According to the newer AR5 report, it is 1.5 to 4.5°C, i.e., the likely equilibrium sensitivity is now known less accurately. But they write:  “This assessment reflects improved understanding”. How ridiculous can you be?

More seriously, let me put this in perspective with the most boring graph I have ever plotted in my life. Below is the likely range of climate sensitivity as a function of time. As you can see, with the exception of AR4 with its slightly smaller range mentioned above,