Now Professor Hansen has responded to the critics of his team’s work and also provided a more layman’s introduction to the significance of their work. They also link to a really excellent popular level discussion of the whole business by Richard Kerr, showing that the argument for reticence is really so 20th century: Only kidding. That argument is incorrect because so much more, now, is known about physics and numerical modeling of these things.
Ice sheet models are very sluggish in response to forcings. It is important to recognize a great difference in the status of (atmosphere-ocean) climate models and ice sheet models. Climate models are based on general circulation models that have a long pedigree. The fundamental equations they solve do a good job of simulating atmosphere and ocean circulations. Uncertainties remain in climate models, such as how well they handle the effect of clouds on climate sensitivity. However, the climate models are extensively tested, and paleoclimate changes confirm their approximate sensitivities. …
Our simulations were aimed to test my suspicion that ice sheet disintegration is a very nonlinear phenomena and that the IPCC studies were largely omitting what may be the most important forcing of the ocean: the effect of cold freshwater from melting ice. Rather than use an ice sheet model to estimate rates of freshwater release, we use observations for the present ice melt rate and specify several alternative rates of increase of ice melt. Our atmosphere-ocean model shows that the freshwater spurs amplifying feedbacks that would accelerate ice shelf and ice sheet mass loss, thus providing support for our assumption of a nonlinear ice sheet response.
Our analysis, however, is based on much more than the climate simulations, as it relies on a huge body of research by the relevant scientific communities, as indicated by the 300 references. Our analysis is based on about equal parts of information gleaned from paleoclimate studies, climate modeling, and modern observations of ongoing climate changes.
Also, I learned a bit more about their paper and the journal where it is being published (Atmospheric Chemistry and Physics Discussions, 15, 20059–20179, 2015). In addition to the open source nature of that journal, which I’ve already addressed, and the desire by policy they have to fix the gap between article submission and availability, it turns out that critics saying “Oh, the paper was released without being peer reviewed” don’t have it quite right. Atmospheric Chemistry and Physics Discussions won’t present a paper for discussion on their site unless it has received a preliminary review by a group of specialists, one which is not a full peer review, but one which assures the stuff isn’t rubbish. For example, a bunch of the stuff at The Watters (if you visit, bring two essential guide books, though: this one and this one) would never make it, and, I’m sure, much of the stuff I’ve written here, not at all intended to be formal publication, wouldn’t make it either. Hansen, Soto, et al did make it through that review. This is simply a matter of scientific practice and the public catching up with the needs of modern scholarship. As I wrote elsewhere, anyone who actually practices in technical fields does not wait for the peer-reviewed copy of a paper to be published before they read and study it. That takes way too long. You go to a place like arXiv.org or, for that matter, Atmospheric Chemistry and Physics Discussions to read papers, and do your own personal peer review. Sure, you revisit the paper once the review is formal, but, meanwhile, research gets done.
Clarifying update from Professor Hansen
See his blog post, reproduced below:
Ice Sheet 200-900 Year Time Scale
Yikes! It has been pointed out to me that the specificity of 200-900 years in my post about ice sheet time scales has the potential to be very unfair to specific individuals. The example that was shown to me was a paper by Ian Joughin published in Science 16 May 2014 in which that range of time scales is mentioned. Joughin is a brilliant young scientist making major contributions to our understanding of ice sheets via numerous field investigations in Greenland and Antarctica, as well as via state-of-the-art modeling, a combination of skills that most of us can only dream of. The time scales that he obtains come out of the modeling, not from pressure to avoid the uncomfortable 100 year time scale that policymakers consider relevant.
I apologize to Joughin, his co-authors and any other scientists who may have a similar situation. It was my fault for not thinking through possible repercussions of my presentation. I should have stuck to discussion of the amplifying feedbacks that we identified and their potential to reduce the time scale for large sea level rise.