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Oh dear Jim, as opposed to claiming that thrust faults can progress 26 miles in a day?! I'll take an appeal to authority over that any day of the week. The point is that there is a very great deal of detailed understanding about glaciology and glacial hydraulics out there, and it is really unwise to toss that out in favour of hitherto unsupported conjectures, unless you have a very good evidentiary basis for doing so. Diving into hypotheses without the understanding of existing literature is just the kind of thinking that has tied many climate skeptics in knots: it would be a shame to see any good people round here fall into the same traps. If people think they can do better on their ice sheet mechanics than Tad Pfeffer, Doug Benn, Bob Bindschadler, Pete Nienow, Martin Sharp and all the rest of the glaciological community, then that's great, and good luck! ... but do so in the light of the published literature, not in spite of it! I apologise if that sounds hard, but the quickest way to make serious mistakes in science is to ignore what has gone before.
Of course, LRC, I'm neither suggesting that current ice sheet models and physical understanding are perfect, nor are they immutable to change in the light of what is a pretty much unprecedented forcing. It would go without saying that I am extremely concerned about how much faster the sea ice melt has been compared to the models, and I imagine that is pretty humbling for those coding the sea ice components of existing GCMs. But for the GIS there is a lot that glaciologists already do know about glacial hydrology and ice sheet monitoring, and I am unconvinced that M Owens is sufficiently aware of that body of literature - hence I was unconvinced by the original hypothesis. I'm reading M Owens as speaking about the whole ice sheet, not small parts of it, which may be susceptible to stagnation. M Owens' original comment certainly appears to refer to the whole ice sheet. Maybe (s)he's right, but I don't think the drainage hypotheses are feasible, as I have explained, as some hopefully "constructive feedback". You shouldn't confuse brief summit melt events with the kind of melting that goes on in the slush and ablation zones, which takes a very great deal longer and more persistent melting. When we see the kind of melting at the ice sheet summit that we see lower on the flanks of the ice sheet, which takes a lot more energy and time, then there will be a great deal more to be concerned about! When we see ice sheet stagnation (such that the surface profile of the ice sheet is no longer convex, driving ice flow and hydraulic pressure gradients outwards), caused by dynamic thinning and surface melt, then equally there will be a lot to worry about. But IMHO there's a fair way to go before either of these things happen.
M Owens - how familiar are you with glaciological literature, particularly on englacial/subglacial drainage, ice sheet plumbing, formation/stability of subglacial lakes, and concepts like hydraulic potential? Also on monitoring of englacial/subglacial lakes through interferometry, altimetry and radar? How do you get significant meltwater to the base of the centre of the Greenland Ice Sheet when the centre is dominated by the "dry snow zone", and subglacial drainage flows towards the ice sheet edge, driven by pressure gradients? How do you pool large amounts of meltwater under the ice sheet when stable pooling regions are under the ice divides (under the dry snow zone)? Why do you think the subglacial hydraulics are insufficient to evacuate the meltwater reaching the base, most of which is entering near the margins and leaves at the margins due to the large hydraulic pressure gradients present on sloping parts of the ice sheet? I think there are a lot of questions remaining with your hypothesis, and there's a lot of research out there with which you can improve your ideas.
Jim, if you're comparing GCMs or ice sheet models (two different things in themselves) with hurricane models, I think you're comapring apples with grapefruit. And as such, I think you lose a lot by allowing doubts based on weather models to colour your views on GCMs - which have a great many successful elements, even if some, like the sea ice, are clearly poorly represented. And I don't think you've really supported your 20:18 point about sea level - just look at the past century as an example - all the sea level rise didn't happen in a single year! As such, there is very good reason to think that rises can happen at rates comparable to the averages, rather than individual catastrophic events. We should still be concerned about the rate of acceleration in SLR, and keep a close eye on the ice sheets for signs of more rapid changes of course.
Catastrophism also depends upon your frame of reference. Sea level rise over the past century has been apparently gradual, with acceleration up to the present 3mm/a. But on the scale of the Holocene, it's extremely fast! A palaeoclimatologist 100,000 years in the future might have trouble determining if it was a single "catastrophic" event or not, rather than a progressive gradual rise. [which is very fast for geological timescales] For glaciers, it depends on topography - which is of course why the WAIS is more susceptible to rapid deglaciation than the GIS. The question is most probably a matter of when the WAIS will go fairly quickly, and surely more quickly than the GIS (Jim I think we're in agreement there), but the tipping point for the WAIS is unknown - it may be soon, may be some distance away. When it goes, it's worth bearing in mind that what the Earth thinks is catastrophically quick, and what shows up in the palaeoenvironmental record as quick, on human timescales may be "slow" (ie notably longer than a human lifetime).
Lennart - don't get me wrong, I'm not advocating ignoring SLR! My thoughts are that I do not expect the GIS to suddenly collapse, given its configuration. The current forcing is very large, but as far as I know, it's not (yet) big enough to waste the ice sheet entirely and quickly, and there is an awful lot of ice to melt there. But if you're in the Netherlands, I can certainly sympathise that SLR would be the first concern. Jim - "palaelogical"? (palaeoecological, palaeoenvironmental?) There's copious evidence for gradual changes over time, as well as some rapid, dramatic events. You cannot compare a glacial lake drainage flood (which is always going to be rapid) with other ice processes like melting or glacier retreat (or any number of other geomorphic processes), which can perfectly well be gradual. Even with the large forcings involved, you need to find a way to allow 3 million cubic kilometres of ice to melt or discharge quickly into the sea. With mountains round the edge of Greenland, this is not as easy as it first appears. The best estimates are that deglaciation will take many hundreds, perhaps thousands of years. The estimates could, of course, be wrong, but there is no a priori reason to think so... yet. Knowing a little about thrust faulting from the Moine Thrust in Scotland, I'd be interested if you could point me to a reference suggesting that the Lewis Thrust occurred and moved 26 miles "in less than a day"? Aside from the obvious issues in dating such an event so precisely, the only reference I found suggested it occurred between about 72 and 58 million years ago. A day seems a wee bit fast for 26 miles of fault movement? Catastrophism has its uses (K-T springs to mind) but is not the only answer to every question. Gradual processes have played a big role in shaping many landscapes.
Lennartvdl, my knowledge is a lot more limited than the likes of Hansen! You'd get a better and fuller answer from a professional glaciologist or ice sheet modeller. If I were to stick some flags in the sand, so to speak, I'd go for 1-2m SLR by the end of the century, based on gradually accelerating contribution from the ice sheets. I suspect Hansen may be on the high side, but a lot depends on processes that we are not completely on top of, such as encroachment of warm water under ice shelves or dynamic acceleration of ice streams. There is an outside chance that ice sheets have the potential to deliver a much larger burst of SLR (along the lines of a Meltwater Pulse 1A, up to 10m/century), but I don't think Greenlnad has a suitable configuration for such an event. West Antarctica on the other hand might have more potential for that - much would depend on the consequences of the loss of the Ross and Ronne-Filchner Ice Shelves, whenever that happens. But such an event could be many centuries into the future, or even not at all. To me, the most likely actual outcome is of a gradual acceleration of sea level rise over the coming centuries, until the ice sheets return to being in mass balance with atmospheric temperature. That may result in total loss of ice sheets and large sea level rises (dependant on whether we find a way of sequestering CO2 and how warm the planet gets), but that ice sheet loss will be (so far as people are concerned) a "slow" process. It's quite enough SLR for low-lying cities and countries to worry about, but I'm more concerned in the short term about ocean acidification and of the impacts of temperature rises/albedo changes/weather pattern changes on agriculture. Not that we should take our eyes off any one issue to solely focus on another!
M Owens, I don't think your first four points are very physical - you're neglecting that moulins close up as well as open, that ice flows (thus destroying moulins and englacial conduits), that the interior of an ice sheet is very cold, and that most water that reaches the bed drains from under the ice, driven by the very large lateral pressures. Most moulins are nearer to the edge of the ice sheet in the ablation and slush zones, locations from which it is hard to pool water under the middle of the ice sheet. At the risk of suggesting teaching a grannie how to suck eggs, I'd recommend reading up on glacier processes (Benn and Evans "Glaciers and Glaciation" or Paterson "Physics of Glaciers" might be a good start), and perhaps having a good read of research publications concerning englacial and subglacial hydrology. If this is all old news to you, please forgive me, but IMHO your hypothesis as it stands is not viable. I'd be quite concerned enough with accelerated glacier flow and surface melt. But with Greenland's topography not conducive to a rapid collapse (peripheral mountains to hold back the ice sheet and restrict access of seawater under calving ice streams) we can reasonably hope that these processes, while operating fast on a geological scale, will be slow enough to give us good time to adjust to the large SLR implications. But there's plenty else to be concerned about in the meantime (weather pattern changes not least)!
Hi Patrick, excellent to see you here again! Re the green tinge, I commented yesterday on SkepticalScience about it, and agree with Patrick. "my guess would be it's something to do with how the open water is appearing with low sun angles - looking at yesterday's[two days ago now] mosaic (and the previous two days too), you can see a distinct latitudinal lower limit to the greenish tint on the right-hand side of the Arctic mosaic - looks a lot like wherever there's open water above ~80N there's the green tint, perhaps the blue spectral channel is not getting as good signal at low sun angles." Expanding on the idea a little, ocean water is likely to be predominantly visible in blue and green channels of the MODIS visible light imagery. Scattering of some blue light at low Sun angles may cause the resulting parts of the image to appear more green than they would otherwise. You would expect the green tinge to spread a little further south as polar night extends in from the north.
Toggle Commented Sep 19, 2012 on Minimum open thread at Arctic Sea Ice
Hi A4R, yep, it will be interesting to see what damage the winds and seas do with these storms. One thing I'd add to my last comment is that context is key for winds in extratropical lows - winds in a storm that is proximal to a strong area of high pressure will be much higher than winds in a storm proximal to a very weak area of high pressure or near other areas of low pressure, due to the greater pressure gradient in the former case. I guess that is quite different from tropical lows, which tend to form in a relatively uniform surface pressure field, and so surface presure in a tropical storm is much more closely related to wind strength. Quite apart from everything else of course!
Toggle Commented Sep 18, 2012 on Minimum open thread at Arctic Sea Ice
A4R - one quick note - you can't compare the Arctic low pressure systems with hurricanes through their central pressures, as they have different formation mechanisms, different environments, different moisture/energy supplies. A 980mb extratropical low where I come from (Scotland) would barely be worth talking about, and winds would certainly be much much lower than in a hurricane (gales if you are lucky). That said, it's a fair chance they won't help ice formation if they drag in some warmer air and curn up the sea a bit. Ice is clearly forming in the fjords of north Greenland (MODIS), so surely, surely, the melt season is going to come to an end soon! How long can all that warm open water resist the cold?
Toggle Commented Sep 18, 2012 on Minimum open thread at Arctic Sea Ice
13C/12C ratio (both stable isotopes) also has its uses - it can tell the difference between CO2 derived from organic matter (plants prefer to take up the lighter 12C) and CO2 derived from inorganic matter, e.g. volcanoes. The main use of this is to show that CO2 emissions over the last century are not volcanic in origin but have an organic source, as the 13C/12C ratio has been declining (see part 5 of Climate Change Cluedo as a good example)
Richaburton, I think no on both counts - First, 10-day forecasts of an individual low pressure system are so unreliable as to be essentially worthless. And that counts for the well-monitored basins such as the Atlantic, where you have a better chance of forecasting weather systems many days out as the initial conditions are better monitored. Beyond 5-7 days and the models diverge greatly on existence, intensity and position of weather systems. Probably best not to rely on individual forecasts more than four or five days out for the Arctic, where monitoring is more sparse. My guess would be that the low you saw forecast was gone on the next forecasting model run (for GFS, 6 hours later). Tropical cyclones/hurricanes whose remnants make it into the North Atlantic tend to get gobbled up by the lows that are progressing across that part of the world. Once they've lost their "tropical" characteristics they're just another low, and are barely noticeable as they cross the likes of Iceland or Britain, where deep lows are common anyway. Most tropical cyclone remnants will quickly merge with another low, producing little noticeable change in that low's intensity. By the time they reach Britain or Iceland it's just another bit of rain! Where the next "Arctic cyclone" will come from is anyone's guess, but it's much more likely to be spawned locally (e.g. off the Siberian coast) and intensify from there in the right conditions.
Don't think Petermann itself has changed much (comparing the 250m images of day 250 and 256, the ice front remains about stationary and doesn't visibly calve back (though there's a fair bit of room at a 250m resolution!) but in betweentimes, some sea ice from Nares wandered in towards Petermann up to day 254. It's an interesting coincidence that the extra debris appears as some sea ice, which had been gradually entering the fjord over the preceding few days, gets blown to one side. It's plausible that the bright white material next to the ice front is little more than a mash of the sea ice, but also plausible that the same conditions that brought and moved sea ice into the fjord, triggered some small calving.
Toggle Commented Sep 13, 2012 on Petermann calves again at Arctic Sea Ice
Sphaerica, while I certainly can't comment "knowledgeably" about your idea, it will definitely be something worth watching over the next year or two. There's a high chance that it will fairly quickly become obvious if the Laptev Bite will be a repeated feature that grows towards the Pole in succeeding years. NeilT, they are certainly nice images. What's intriguing to me is the appearance of several patches of low concentration ice on the north side of the Canadian Archipelago. Along with the substantial melt-out in the NWP and within the CAA, it's almost as if the melt is eating into the ice up against the north side of the CAA. A disclaimer is that these low concentration patches may be entirely wind-created, and may have appeared in previous years (I haven't checked), but regardless of their origin, they are not going to help the quality and thickness of the ice in what is supposedly one of the last 'havens' for ice in the Arctic.
Toggle Commented Sep 11, 2012 on Minimum open thread at Arctic Sea Ice
Bob Wallace - intersting observation. I think recently a 'dam', created by grounded icebergs at the fjord mouth, broke. Somewhere between day 234 and 239 (on MODIS imagery), there was a large flux of bergs out into the open ocean from Ilulissat Fjord. Over the following five days, a great many of the bergs in the lower half of the fjord were able to exit, partially clearing that bit of fjord. Meanwhile, the ice up near the ice front progressed rapidly down the fjord from day 239 (as marked by the evolution of a dark streak of material among the bergs near the ice front between day 239 and 243), mostly refilling the lower part of the fjord with bergs by day 246. A new km-scale berg calved off the southern calving front between day 243 and day 246. The fjord will effectively be "full" again over the next day or so as the mass of ice from the upper fjord finished filling the lower fjord, and it will be interesting to see if a new dam is formed at the fjord mouth. It will also be interesting to see if this change in the Ilulissat fjord affects the overall calving front position, via a loss of back pressure on the calving front.
Kris, you know that in the Jakobshavn images above the long white arm that extends from lower right to upper left is not the glacier, right? It is a mass of icebergs and other ice debris being churned out by the calving fronts which are at the far lower-right of the image. So there has been neither a major recent disintegrating nor collapsing of Jakobshavn as you suggest. What's happened is that the dam, created by big icebergs grounded at the fjord mouth, has released, allowing a lot of the smaller berg debris to escape into the open ocean. In a glacier ablation area, once the surface snow has melted and you're left with bare, solid ice, you don't get colour changes driven by "developing fluid water under the surface", as the ice is simply not that permeable. Water can accumulate in snow-covered areas, changing the colour of slush, and obviously can pond on the ice surface as supraglacial ponds or lakes. Not so much in heavily-crevassed areas near the calving fronts though (dark grey bits at the far lower-right of the images above), and not into bare ice (as the lower parts are at this time of year).
Toggle Commented Aug 31, 2012 on ASI 2012 update 10: (wh)at a loss at Arctic Sea Ice
Hi Werther - I see what you mean about the June calving event, but since then, the calving front has advanced to the point that it is in a very similar position to where it was one year ago (I'm looking at 2012242 and 2011233 on the r02c02 MODIS subset). But in between times, (e.g. 2012200), there have obviously been some big calving events, as you've noted. Clearly the calving front fluctuates a fair bit, perhaps not surprisingly as we know a vast amount of ice goes through the calving front (ice flow >20m/day). So unlike Petermann, what's lost can 'grow back' pretty quickly! It will be interesting to keep an eye on it in coming years, as you have done.
Toggle Commented Aug 30, 2012 on ASI 2012 update 10: (wh)at a loss at Arctic Sea Ice
SteveC and A4R, I think you're misinterpreting the images - Jakobshavn has basically not changed at all in the past year. The calving front is the two concave lobes at lower right, indented into the main ice sheet. The stuff that fills the fjord to the coast is a great mass of icebergs and brash ice. Jakobshavn lost some big pieces last year IIRC, but this year the calving front has remained roughly stationary. It's still calving lots of ice from both the northern and southern arms of the ice stream, but flow is replacing the calved ice, leaving both concave calving fronts where they were.
Toggle Commented Aug 30, 2012 on ASI 2012 update 10: (wh)at a loss at Arctic Sea Ice
Paul, it's really unimportant, but just to acknowledge your earlier comment - I know you thought you answered my question, but you didn't - you avoided it and asked a different question in return (it's easy to get distracted by minutiae). Subsequent comments by folks here, and most importantly by Walt Meier on the ASI update 10 post, do not support your case, and does support the idea that there is a fair bit of really low concentration ice out there, read by IMS and MASIE, and not by Bremen or IJIS. But lets leave this until the dust has settled on a terrible summer for Arctic ice.
Watching Arctic sea ice is that strange mix of fascinating and horrifying. Where now for ice extent, with a few weeks of likely extent loss left. Early or late minimum? Does it even matter that much now? 3.5M sq km? Is 3M sq km possible (probably not)? My take on the last few years has been to watch the ice gradually become thinner and more spread out until this year was little surprise (got too thin). But unlike 2007, I see no reason why 2013 will be anything other than a further new record - a continuation of the thinning, spreading out. To quote Shackleton from 21st November 1915 (with due apology to girls present): "She's going, boys".
Toggle Commented Aug 26, 2012 on ASI 2012 update 10: (wh)at a loss at Arctic Sea Ice
Anyone else looking at the IJIS graph and silently screaming "Pull up! Pull up!", like some kind of air disaster movie where the radar trace of the plane inexorably drops to the ground? I keep expecting to see a significant slowdown, but this year the decline is quite remarkable. What's left is to wonder if we'll have a relatively sudden reversal like 2008or 2011, though we're even faster than both those years (10 day average of 80,000sq km/day rather than 65,000sq km/day). i dread to think how the ice will look if we have a late minimum this year. Any thoughts on whether the fact that the mean ice edge is closer to the Pole might mean for a sooner end to the decline (ie more like 2008/11 rather than 2005/07? Top melt is obviously slowing down now, and compaction/bottom melt is dominant in melting, but perhaps the initiation of the surface freeze-up will reach the ice edge sooner this year than in previous years? Even if true, it's just papering over the cracks, but it will be academically interesting to see if there is a change in pattern because of where the freeze up has to start. But not comforting, in the slightest.
Ned, your post at August 22, 2012 at 15:12 covers a lot of my concerns with Paul's idea. Paul, you didn't answer my question yesterday - do you think it is plausible for two datasets, with differing thresholds for ice detection, to show a similar extent loss curve (down to the 'kinks' caused by large melt events), but with a lag between the two? If not, why not? These conditions, with lots of thin and spread out ice, are exactly the conditions under which you would expect the different monitoring platforms to record large discrepancies. I'm convinced more than ever that all we are seeing is a difference in observation capacity and observation methodology between multiple datasets, observing the same system in slightly different ways. And of course the end result is scary however we look at it!
So hypothesis tests have to come form the last couple of years, fair enough! I've had a look at the Healy images for that date (best accessible here) - certainly interesting; unfortunately the Aug 2011 cruise report track map has a disabled link. If you're right, it's cetainly interesting. What's Peter's take on that? Paul, did you miss my question in the 3rd paragraph of my last comment? What do you think?
Paul, I'm afraid that graph is not convincing to me either ... is it not possible to get a more complete dataset (more than one month, and perhaps over the whole melting season)? From what point are you suggesting teh "delay" is getting worse? Just last year to this year? Over several years? The reson I say this is that since 2009, the ice pack has been visibly thinning and becoming more spread out, especially at this stage of the melting season. So it's not a diagnostic test to say that the 'delay' has been progressively getting worse year-on-year, if the actual ice pack has been more spread out, and so more conducive to lags between the different observing systems. If you can demonstrate that a data delay has been present since 2007 or earlier, then that would be much more interesting, as the pack was much different in '07/'08 than the progressive rotting from '09 through to present. Would you accept that it is plausible that two observing platforms with differing thresholds or measurement systems for determining ice/open water will show similar trends, with a lag between the two? Please don't take my view to be dismissive of yours, but in order for our ideas to survive, they need to survive challenges to their logic.