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Robert Milson
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I would like to follow up my previous post about long term evolution of arctic ice cover with a couple of literature citations. I hope this is on-topic for the current thread. The recent evolution of PIOMAS data is very suggestive of a transition to ice-free summers in the arctic, but, arguably, my post is better suited to a thread devoted to long term arctic ice scenarios. I will happily follow any organizational guidelines from the site coordinators. With apologies for the longish preamble, here are a couple of recent papers that caught my eye: 1. Recovery mechanisms of Arctic summer sea ice, Tietsche, et al (2011) 2. Bifurcations leading to summer Arctic sea ice loss, Abbot, et al (2011) Quoting from the 1st paper: " In our perturbation experiments, we observe how different feedbacks in the Arctic compete to enhance or dampen a strong negative anomaly in sea ice, equivalent to a strong positive anomaly in oceanic heat content. In summer, the oceanic heat anomaly is enhanced by the ice–albedo feedback, but in winter the excess oceanic heat is lost to the atmosphere due to a lack of insulating sea‐ice cover. This leads to an anomalously warm atmosphere, which in turn causes increased heat loss by longwave radiation at the top of the atmosphere and decreased heat gain by atmospheric advection from lower latitudes. A lasting impact of the ice–albedo feedback is not possible because the large‐scale heat fluxes quickly adapt to release the excess oceanic heat from the Arctic." From the 2nd paper "These results indicate that many GCMs do not show strong signs of bifurcation behavior as summer sea ice is lost, although some appear to. This is consistent with our results that a bifurcation in summer sea ice loss would depend on model parameters and, if it exists, would be associated with a relatively small jump in the state of the system and relatively small hysteresis." So what's going on here? The PIOMAS evolution, the record-breaking changes during this year's melt season all seem to suggest a rapid transition to a new regime. However the current models do not seem to validate this kind of phenomenon. Are we misinterpreting the data or will the models have to be adjusted?
I am a first time poster with a question about the possible consequences of the recent dramatic changes to the arctic ice. First off: hats off to the blog founder and participants for pulling together the relevant data sources and for all the illuminating discussions. At a glance, the various graphs show a steady but linear decline in the various ice statistics until 2007. After 2007, the data seems to indicate a non-linear, feedback effect of some kind. It's hard to avoid the conclusion that the system will soon transition to a new steady state of ice-free arctic summers. The ice maximum still seems to be in the linear regime with a steady downward trend subject to some natural variability. Having stated my premises, here are my questions. 1) How stable is the new steady state going to be? Is it possible for the arctic maximum to transition to novel regimes? For example, every winter, despite the warming, Hudson's Bay and James Bay ice over. Is it even conceivable that warming can progress to a point where a body like James Bay will remain ice free over the winter? 2) The transition to ice-free summers in the arctic will have an impact on NH climate -- no doubt. However given that even a thin crust of ice interrupts the transfer of energy between ocean and atmosphere, the yearly refreeze should mitigate and stabilize any such impact. To put it another way, once we settle into the new regime, what will be the significant trends in ice statistics with respect to NH climate impact?
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Sep 1, 2012