[Update: Or, maybe not.]
Via twitter comes news of the sad demise of “Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming is highly dangerous”; Review status: This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). A final paper in ACP is not foreseen. My view at the end of August was that Peter Thorne’s review was “substantially negative about the paper”; it looks like the editor has gone with that and similar views. In essence, its a sad train-wreck; only read on if you like such. I feel somewhat cruel in even blogging it. But Hansen is a big boy, and he chose to put this up in public.
First, timing. I’ve now re-read Eli Follows Up written on the 12th of October (a successor to the critically acclaimed Eli follows through) which tells me that “The editor, Frank Dentener, has closed the open discussion and thrown the paper into the second stage of review… The authors are now expected to publish responses to the comments and reviews”. Which explains the flurry of replies by H on the 13th. In consideration of the review by Drijfhout et al., “Eli judge[d] that the editor will pay serious attention to these arguments and Hansen, et al, will have to meet their challenges”.
But before we get to that, let’s look at a comment by Greg Flato, another serious player. Its not new, but had slipped my attention in the mass of other comments. Its probably the most critical of all – ignoring the nutters, of course.
given the way the paper is organized, it is difficult for a reader to connect assumptions made in the model forcing (sections 3.2 and 4.3) to their justification based on paleo-climate reconstructions (section 2.1) and modern observations (section 7.3). What is important is that the prescribed freshwater forcing scenarios have an exponentially increasing form with doubling times of 5, 10 and 20 years. The most extreme of these has sea level rising 5m by the year 2060. This assumes freshwater flux could rapidly reach values up to 8Sv. To put this in perspective, it is about 1800 times the currently observed melt rate for west Antarctica… Prolonged exponentially increasing ice-sheet loss is clearly unphysical and so the authors arbitrarily terminate freshwater input once the associated sea-level rise reaches 5m – it is zero thereafter… The authors provide no assessment of the likelihood of any of their scenarios, and do not cite most of the previous studies that have explored the response of the climate system to much less dramatic freshwater input… They also do not justify the manner in which this freshwater is introduced into the ocean (as liquid water with a temperature of -15◦C, pg. 20079)… simulated global temperature drops to roughly 1.4◦C below preindustrial levels… This is in striking contrast to essentially all published projections of 21st century climate change, and so places a very large burden on the authors to provide evidence in support of rapid global cooling in the face of rising greenhouse gas concentrations…
Adding the melt to the ocean as water at -15 oC is a “WTF?” moment. Also Flato points out, somewhat more diplomatically, what I said before: hosing is passe, its been done to death. So how do H et al. respond? In a rather long rambly sort of way that ends up with “In all of these model runs we used -15°C as the temperature of the freshwater added to the ocean mixed layer. If a large fraction of the ice sheet discharge is icebergs, the cooling effect would be larger than in our experiments”. So I think the point is that the latent-heat equivalent of dropping the ice in the ocean and having it melt, would be inserting the ice as water at -15 oC. Except, it wouldn’t be: -15 is just a nice round number, as H implies in the reply, actually it should be a different number. Um. And none of this info is in the original paper? I think we’re back at my suggestion: the paper is too long, and clearly needs to be broken up into sub-papers that are manageable.
And… H et al. just won’t learn: having been criticised pretty strongly for mixing science and advocacy, the end of the response to Flato is Let us hope that we are smart enough not to perform an empirical test using the real world with a forcing of the business-as-usual magnitude. Really? Does say to him “please, just don’t say that, this isn’t the place”? I’m speaking as a famously diplomatic person, you understand.
But the make-or-break one is Drijfhout et al.: are six people enough to stand up to Hansen? Well, yes. They start off fairly gently with The analysis does not contain any process that is physically impossible (albeit sometimes unlikely)), nor present principally flawed interpretations of the paleo data (albeit often biased to the upper end of uncertainty measures) but fairly soon get to
The title of the paper is more suggestive than is justified by the scientific evidence. The conclusions
cannot be regarded as being robust, as they are insufficiently supported by both modeling results
which is fatal. H et al.’s response is very short, and is the reply of someone who has given up. The most obvious example of this is
Extreme events are much more likely to occur after 2100 – therefore we recommend to avoid terminology such as “dangerous”. Hmm, yes, I guess that we should not be concerned about anything that happens 85 years from now – the dickens with those characters. The Dutch can migrate to Switzerland, after all.
If you’re going to write that kind of thing, stick to blogs and op-eds.
* “Unfortunately, while computers continually surprise us with what they can be used for, almost nothing is known about what they cannot do.” – via QS
* Science Isn’t Broken: It’s just a hell of a lot harder than we give it credit for. Includes nice p-hacking toy.