Saturday, September 28, 2013

AR5 WG1 Summary for Policy Makers Released

The IPCC Working Group 1  5th Assessment Report Summary for Policymakers (WG1 AR5 SPM in IPCC jargon) was released yesterday. It is the overall summary of the first of three volumes of the 5th AR. The other two will be released next year. We are still working on the final draft of the Working Group 3 report (I notice some e-mails in my inbox about it this morning). The SPM will then go next year for approval by the governments.

This cartoon appeared on The Australian website:

I think it does nicely sum things up. The SPM is pretty similar to previous ones and pretty conservative on projected climate change. Not much different from previous reports. When reading it, I was thinking "Joe Romm won't like this" and also that it was pretty jargon-laden for a report to policymakers. It turns out that Climate Progress is pretty positive about the report, though Romm's own comments are a bit more negative.

One interesting statement (D.1) is:

"There is robust evidence that the downward trend in Arctic summer sea ice extent since 1979 is now reproduced by more models than at the time of the AR4, with about one-quarter of the models showing a trend as large as, or larger than, the trend in the observations. Most models simulate a small downward trend in Antarctic sea ice extent, albeit with large inter-model spread, in contrast to the small upward trend in observations."

This is in the context that it is often stated that Arctic sea ice is declining much faster than  models predict. Another change is that there is now much more information about ocean heat content trends. The words "ocean heat content" don't even appear in the the AR4 WG1 SPM. This time there is a separate section on the oceans (the whole summary is about 50% longer). Ocean warming is also the third point on the really brief headline summary. So this is a change of emphasis based on the better availability of data on the oceans.

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