The Bengtsson paper would have to have been very bad to be worse than, say, Kummler and Dessler, but at the moment we just don't know because we haven't seen it. However, the ERL editor claims that Bengtsson's offering contained errors. Unfortunately she doesn't actually identify any; the only concern in the reviewer report published to date seems to be with Bengtsson's temerity in thinking that observations and models really ought to match up, and of course the concern that sceptics might be keen on the paper.

But there are some errors floating around that are worth a look - as I mentioned earlier a cursory glance suggested to me that the reviewer's report itself included a bit of a boo-boo. I've now been away and done some fact checking and confirmed that I was right. Actually, I'm righter than I thought I was, as I shall now explain. Here's the paragraph in question:

Even more so, as the very application of the Kappa model (the simple energy balance model employed in this work, in Otto et al, and Gregory 2004) comes with a note of caution, as it is well known (and stated in all these studies) to underestimate ECS, compared to a model with more time-scales and potential non-linearities (hence again no wonder that CMIP5 doesn't fit the same ranges).

What struck me - a humble blogger, a mere accountant, a grubby scribe, as my detractors are occasionally wont to say - is that the Kappa model is not actually used in Otto et al (or indeed Gregory 2004). So here we have an expert reviewer who seems to be less familiar with the details of the relevant studies than I am. The reason I know about all this is that it was discussed at Ed Hawkins' blog some months ago. Here's Nic Lewis in the comments thread:

I spent weeks trying to explain to Myles Allen, following my written submission to the parliamentary Energy and Climate Change Committee, that I did not use for my projections the unscientific ‘kappa’ method used in Gregory and Forster (2008)...

...going on to explain that by 'unscientific' he meant that it didn't conserve energy.

And this quote reveals the other problem with the reviewer's remarks. The kappa method is an approach to estimating ocean heat uptake, which assumes that this is proportional to surface temperature change. Everybody seems to agree that the approach is unphysical because it doesn't adjust for 'warming in the pipeline' and indeed the Gregory and Forster paper notes that 'its validity is restricted'. But the important point is that it is only relevant to projections of future warming anyway. It has no relevance to energy budget estimates of climate sensitivity, which are backward looking.

But the reviewer who recommended the rejection of Bengtsson's paper did not understand this.

Scary eh?