by Judith Curry

[Marotzke] attributed the oversight to a tendency of each group working on each of the 14 chapters to rely on some other chapter to deal with the issue. And anyone who was thinking about it at all thought some other chapter should handle the issue. – CS Monitor

Ok, now I understand how the IPCC forgot to mention the pause. The Christian Science Monitor has an excellent article on the recent AR5, entitled UN Panel: ‘Extremely likely’ that human activity behind most global warming. Excerpts:

Scientists in the first working group also have tried to tackle the issue of the pause in surface warming that has marked the past 15 years – although they came to the issue a bit late in the process, acknowledges Jochem Marotzke, director of the Max Planck Institute for Meteorology in Hamburg and a lead author on one of the main volume’s chapters.

Some 200 authors involved in the first report met in Hobart, Australia, in January for a final gathering to hammer out wording, in light of reviews they had received on a previous draft.

“We got quite a few review comments on various chapters saying: What’s going on here? We need to assess what we know” about the hiatus, he said during a briefing Friday morning.

He attributed the oversight to a tendency of each group working on each of the 14 chapters to rely on some other chapter to deal with the issue. And anyone who was thinking about it at all thought some other chapter should handle the issue.

The result is a statement that the slowdown in the rate of warming over the past 15 years is – with medium confidence – due equally to natural variability in the climate system and to a combination of changes in what researchers dub climate “forcings”: in this case accumulated aerosols from a spate of midsize volcanic eruptions in the late 1990s, which have a cooling effect, and a decade that spent most of its time on the downside of the sunspot cycle. As the number of sunspots fall, solar radiation reaching Earth is reduced. While those reductions are tiny in absolute numbers, researchers have uncovered mechanisms by which the climate system can amplify the effect of those small changes.

“This does not mean that global warming has stopped, because the ocean is still taking up heat, sea level is still rising, ice is still melting everywhere we look,” Dr. Marotzke said. Instead, he suggested, this likely is a confluence of conditions where, in Yahtzee terms, the system rolled three dice and all came up sixes.

Still, the group, which relies on studies published in peer-reviewed journals for its overviews, didn’t have much to go on, acknowledges Working Group 1’s co-chairman, Dr. Stocker. “I’m afraid to say there is not a lot of published literature that allows us to delve deeper into the required depth of this emerging scientific question,” he says, citing a lack of adequate measurements of ocean heating, especially in the deep ocean, as one hindrance. This is one mechanism scientists have proposed for moderating the rise in surface temperatures.

One explanation that scientists skeptical of this explanation have offered for the failure of climate models to foresee this hiatus holds that the models reconstruct a climate system that is too sensitive to rising CO2 concentrations.

ndeed, the new report modifies slightly the IPCC’s estimate of how touchy the climate is to changes in greenhouse gas levels compared with the reports the IPCC issued in 2007.

Then, researchers estimated that if CO2 concentrations doubled over pre-industrial levels, one could expect global average temperatures to rise by 2 degrees to 4.5 degrees Celsius (3.6 to 8 degrees F.), with a 3-degree increase as the most likely. Friday’s summary widens that to 1.5 to 4.5 degrees, with no figure given in the summary as a most-likely number.

JC comment: Ok, I appreciate Marotzke’s honesty. But don’t the IPCC authors ever read the newspaper or blogs or anything? How did they miss the fact that the pause is the most important issue in the public debate on climate science, for well over a year now? All this is written for the policy makers, n’est pas? Well of course they might have spotted this in the peer reviewed literature if they hadn’t been so busy with that gate keeping thing.

To me, Marotzke’s statement is much more believable than Michael Oppenheimer’s statement in a PBS interview:

MICHAEL OPPENHEIMER: Well, Roger is completely wrong about the so-called hiatus. That is, the scientists looked at it very carefully. There’s an extensive discussion of it in the detailed background documents will be made public on Monday.

Well, it will be fun to start digging through the WG1 report to find where all this is buried.

Roger Pielke Jr. on twitter sums it up this way:

IPCC–> there is a big difference between saying “we don’t know, emerging area of research” and “nothing to see here, move along”