On Hansen et al: Critical response to recent sea level rise publication

I have a lot of sympathy for what Hansen is doing. He absolutely is going out on a limb, scientifically speaking, and using PR tactics to generate mainstream media coverage for his research.

At the same time, nearly all the critical responses here acknowledge what he is saying is within the realm of possibility. They mainly argue it's not a proven or likely outcome. Which may be true.

But I think climate science, maybe science more generally, needs to ask itself some existential questions here. We're not talking about the need for 5-sigma confidence before announcing the Higgs Boson here. We're talking about the future of the planet and human civilization. So to what extent should climate scientists do their best to really hammer home to the public the range of possible outcomes, and specifically how bad things conceivably could go, how much we can't say for sure?

In part I think climate scientists specifically have learned to be extremely cautious in what's stated publicly, because of the amount of firepower directed towards discrediting them.

But what Hansen himself stresses is that "the major scientific issue that exists is how rapidly ice sheets can respond to the unprecedented human-made climate forcing, not whether they will respond. In our present paper we present substantial, compelling evidence that the ice sheet response will be non-linear and more rapid than has generally been acknowledged."

This statement I think is much harder to argue, and almost certainly most climate scientists who have studied the issue would agree, if only in private, that the IPCC predictions for sea-level rise are likely to be far more conservative and linear than what emerging science regarding paleoclimate, ice sheet dynamics like hydrofracturing, the geomorphology of Greenland and WAIS especially, ocean circulation, etc are indicating will actually happen.

The ice sheet melt rate was predicted to be relatively linear prior to detailed modeling of the specific dynamics in play. The more we understand about the details, the worse the situation looks, and Hansen is one of the first to try to pull those threads together and look anew at the big picture.

I would also highly recommend reading through some of Thorne's detailed review comments[1]

It's clear he thinks the paper is extreme but nowhere near ridiculous, perhaps except regarding the "boulder" issue (which seems his best argument, but tangential). Specifically the Eemian, the IPCC/AR5 defenses, the non-linearity. A lot of it is disagreement over tone and maybe Hansen dialing things to 11 instead of an 8 or 9.

I sort of agree with both of them, but the larger issue is the public sees this whole thing as maybe a -3 to 2 level of severity and they're arguing over 9 or 11.

[1] http://www.atmos-chem-phys-discuss.net/15/20059/2015/acpd-15...

TL;DR:

This blog post gives a review of the many good scientific criticisms of the Hansen paper, and also highlights the poor responses of Hansen et al.

Basically, the paper starts with the assumption of exponentially increasing melting from Greenland and Antarctica, modelled simply as Ce^(at) liters of fresh water added to the ocean per year. The weird thing IMO is that this (liquid) fresh water is injected at -18 C (weird model), so they've effectively removed the latent heat but not the sensible heat, for some reason; the latent heat is 10x the sensible heat here, so why neglect the big one and include the small one? They conclude that dramatic sea rise occurs (duh). Perhaps the most important takeaway from the critique in this blog post:

""" [The paper predicts that] basically many areas, in Europe in particular, enter a period at least as cold if not colder than the little ice age. The associated rainfall changes are equally as impressive. This would lead to large-scale challenges around provision of food, services etc. for global society and large-scale disruption of ecosystems. It is also entirely opposite to the direction of climate change that policy makers are currently planning for on this timescale. """

So, if the paper's conclusions are correct (and the blog post author and many others apparently think it's not), we're basically doing everything wrong in preparing for the consequences of climate change.