Tomorrow at 10 am Amsterdam time the SPM will be released. Leaks have been around for a while so everybody knows what’s in it. Things might have changed though.

I think one of the key issues in the SPM is climate sensitivity. I have been working on a reaction to AR5 together with Nic Lewis (we were both expert reviewers) which we can hopefully publish in the coming weeks.

So what did the final draft of the SPM say about climate sensitivity:

The equilibrium climate sensitivity (ECS) quantifies the response of the climate system to constant radiative forcing. It is defined as change in global mean surface temperature at equilibrium that is caused by a doubling of the atmospheric CO2 concentration. ECS 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). The lower limit of the assessed likely range is thus less than the 2°C in the AR4, reflecting the evidence from new studies of observed temperature change using the extended records in atmosphere and ocean. {Box 12.2}

Most surprising is that they don’t give a best estimate. IPCC has always given a best estimate, sometimes of 2.5°C and other times of 3°C.

So this paragraph is the first thing to watch tomorrow 10 am.

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