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 me

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.