Matt Ridley has an article in the Wall St Journal today, looking at how the forthcoming Fifth Assessment Report is handling climate sensitivity and the halt in temperature rise. Most of this will be familiar stuff to BH readers. Here's how he concludes:
Since the last IPCC report in 2007, much has changed. It is now more than 15 years since global average temperature rose significantly. Indeed, the IPCC chairman Rajendra Pachauri has conceded that the "pause" already may have lasted for 17 years, depending on which data set you look at. A recent study in Nature Climate Change by Francis Zwiers and colleagues of the University of Victoria, British Columbia, found that models have overestimated warming by 100% over the past 20 years.
Explaining this failure is now a cottage industry in climate science. At first, it was hoped that an underestimate of sulfate pollution from industry (which can cool the air by reflecting heat back into space) might explain the pause, but the science has gone the other way—reducing its estimate of sulfate cooling. Now a favorite explanation is that the heat is hiding in the deep ocean. Yet the data to support this thesis come from ocean buoys and deal in hundredths of a degree of temperature change, with a measurement error far larger than that. Moreover, ocean heat uptake has been slowing over the past eight years.
The most plausible explanation of the pause is simply that climate sensitivity was overestimated in the models because of faulty assumptions about net amplification through water-vapor feedback. This will be a topic of heated debate at the political session to rewrite the report in Stockholm, starting on Sept. 23, at which issues other than the actual science of climate change will be at stake.