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Chris Reynolds
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Bill, I'm pretty sure that when the April thickness is low enough for a <1M km^2 extent for September we will see a June ice loss that will outpace anything we've seen to date, that by July it will be obvious we're in for something big, but that losses in August will probably be less than the current average. Novastellar, The problem with ocean currents is we have no data that informs us within the melt season. As for longer term and more regular impacts: As an example, try Nghiem 2012 - "Seafloor Control on Sea Ice" In that paper various cases where ocean bathymetry and currents have repeated impacts on ice are discussed, throwing light upon the shape of the ice pack at various times of the year (or maybe it's just at maximum and minimum - not read it for years).
Thanks Nightvid, The image I was thinking of was fig 1b in this article.
Bill, I've been deliberately keeping myself in the lab today, temperature and humidity controlled. :) No such luxury at home though. :(
Blaine, The Rahmstorf paper was covered by RC back in March. With an interesting addendum on cold US winters on the Eastern seaboard. Not relevant to this discussion. I find what you write interesting, but suspect that if you're right then there is a modifying role for the AMOC + the post 2007 ice state. Lindsay & Zhang proposed a trigger point in the mid 1990s for a period of self-accelerated ice loss due to the ice albedo effect. This would coincide with the AMOC going positive after 1993. So did the AMOC cause the loss of ice? A key issue here is; to what degree would the AMOC make its effects impact a model like PIOMAS? One route would simply be the incorporation of sea ice concentration. However Lindsay and Zhang find that the post 1990s decline of volume is driven by the ice albedo effect in PIOMAS, and interpreting that decline instead in terms of the AMOC as driver brings the problem that the AMOC was stronger before 1970 than during the 2007 to 2012 period. The AMOC is shown to have substantially reduced over the last century. Would the previously higher AMOC not act against sea ice? A clue here is the emergence of strong Arctic Dipole pattern since summer 2007, and it maintenance until 2012, when the AMOC reduced. This is why I suspect more of a modulating influence on reduced thickness in the 2007 to 2012 period. However the third year in a row with a failure of the 2007 to 2012 dipole set up seems to me to need an explanation (assuming it doesn't re-assert itself later this year or in years to come. And what you suggest seems to be reasonable. Have you contacted anyone like James Overland or Stefan Rahmstorf about this? I ask about Overland because of this paper.
Thanks for the added detail OSMM, I was right, I had totally misremembered what your method was about. But I wonder if a similar mechanism was at play in the 2013 'rebound' as that which would apply to Larry Hamilton's sigmoid fit. How long is the persistence of data in your model? I am wondering if the rebound found in 2013 was due to a return to 'trend'? I am assuming that the constant offset is negative and would act in a similar manner to the 'trend' of a sigmoid fit. The fails in 2012 is not surprising, there is a graphic at SIPN/ARCUS that shows similar fails for the suite of models in 2012. But in a rushed search just now I couldn't find it. I will think about this today, but have to get off to work now.
Navegante, Thanks, but speaking for myself, I'm doing nothing but implementing an idea that is quite common amongst the proper scientists. And whilst I doubt it, I could still be wrong this year. John Garland, Denialists? Yawn...
OSMM, How did your model hindcasts handle the 2013 minimum? Can your model predict with smaller bounds than mine (+/-0.64) the September minimum using April data? I ask because I struggle to see how it can work without taking into account volume, when volume goes up, as in 2013, after volume crashed so low in 2012. Perhaps you could link to where you've explained the model on the forum - I can't recall the details, sorry. But I use Larry Hamilton's extent trend approach as a baseline any method must do better than, and I remember your method as being similar (on which I am very probably wrong!) In terms of similarity to Zhang's PIOMAS my method is similar, but that isn't really informative as we both will use initial thickness in PIOMAS. After that weather variability is approached differently, although Zhang has a range of 1.2, and I'm 1.28 - not that much worse. In terms of thickness, the distribution is far from constant over the 1979 to 2015 period. Loss of volume has come from thicker ice, with first year ice volume increasing to make up for the loss of multi-year ice. FWIW here are my hindcasts from 1979.
PS Robert, See page 16, figure 2 of this presentation.
Jim, Yes, we're probably not going to have a repeat of 2013/14, but I'm not persuaded that a re-run of the 2012 crash is likely. I think that at best we could get close to 2007/2011, but in the context of the post 2007 period neither of those are crashes. Navegante, The compactness isn't compared to 2007, the figures I give are for average compactness from 10 June to the latest data. In terms of anomalies... Laptev compactness is average (for 1981 to 2010). ESS compactness has been rising from low levels on 19 June to near average on 27 June. In comparison 2007 and 2012 were falling through the floor at this stage. Chukchi compactness continues to fall. Beaufort compactness continues a modest fall. Note that where anomalies fall losses are greater than average, level anomalies means average losses, rising anomalies mean losses that are less than average. I too would be surprised if we end up above 2013 or 2014. Robert S, Simmonds et al "Dramatic interannual changes of perennial Arctic sea ice linked to abnormal summer storm activity." "Strong relationships are revealed between the September sea ice changes and the number of cyclones in the preceding late spring and early summer. In particular, fewer cyclones over the central Arctic Ocean during the months of May, June, and July appear to favor a low sea ice area at the end of the melt season. " Low pressure dominance during the months around the peak of insolation makes for cloudy weather that shelters the ice from direct sunlight. Thus reducing initial thinning of the pack. Low pressure dominance at the end of the melt season, August/September, provides low clouds, enhanced back radiation, which makes up for reduced insolation as September approaches and the sun sets. This enhanced back radiation acts to melt ice. Also storms will act to vertically and laterally mix the ocean bringing warmer water into contact with the ice.
Larry, Jim, I agree with Larry, and whoever said 'If it walks like a duck...' Whilst there are various individual motivations for SIPN predictions it should be borne in mind that the driving force of the project is to improve prediction, hence I guess the cocentration on modelling rather than statistical approaches. Modelling being more likely to be amenable to substantial improvement. Those using trend extrapolation of volume loss to reach the conclusion that sea ice free state is imminent may be couching the statements in terms of 'if... then...'. But it is naive to expect lay people not to take them as predictions. **** Now for what I came on here to say... I am now getting pretty confident that we won't see a crash this year. In both CT Area and Wipneus's calculation of area the June anomaly 'cliffs' have been muted and have been followed by a levelling. I have previously shown that Late June Compactness in the peripheral seas of the Arctic Basin (Beaufort through to Laptev) 10 to 30 June average compactness dropped to 0.7 in 2007 and 2012. And that this might therefore be used as an early warning of impending large summer losses. Now, with three days of data to go, this late June average compactness is 0.74, 2013 was 0.77, 2014 was 0.77 for the same period. Both 2007 and 2012 were 0.70 for the same period. ***** Susan, "However, I do worry about "barking mad" kinds of geoengineering which are getting heavy advocacy from that quarter." Same here, I once knew an old lady who swallowed a fly...
L Hamilton, I was initially confused by what Wadham's was doing. Now I think the clue is in the explanation of method. "The uncertainty (large) concerns to what extent the area returns to the trend line, having made positive excursions in 2013 and 2014." Which makes me think the purpose of Wadham's prediction is more to set a test of how far off the 1979 to 2012 trend we will be this September, rather than being an actual prediction. This interpretation may of course be clouded by my not expecting a 'fast crash' and expecting a comparatively slow transition over the next 20 years or so. But I find it hard to believe Dr Wadhams is seriously suggesting 1 million this year.
Osteopop's back, and channelling James Delingpole. Again... "Anyone fancy a pint?"
Susan, The arctic region is covered by a grid, you can see the NSIDC 25km grid by going to cryosphere today, the regions map there is a grid, each pixcel represents one grid box. Satellite microwave brightness is used to work out the concentration of ice in each grid box. And concentration is given in a table of numbers, one for each box. Wipneus uses this gridded data to work out area and extent. You know what they are I presume? Basically, if concentration drops away from the ice edge within the pack area will drop. But unless concentration goes below 15% extent won't drop. In that case Neven's CAPIE index will fall, and we'd say that the pack becomes more dispersed. Where most of the loss of concentration is from the region around the ice edge both area and extent fall at the same rate. In such a situation Neven' CAPIE index would remain roughly level. I use compactness, area divided by extent, that has been fairly average all June so far. this suggests that through June so far the loss of ice concentration within the pack has bee normal. In years like 2007 & 2012, there was a lot of loss of concentration from within the pack, so by this time in June CAPIE (and compactness) were falling faster than normal. Hope this helps, if not just ask.
Toggle Commented Jun 15, 2015 on Melt Pond May 2015 at Arctic Sea Ice
Rob, It's a melt pond model augmentation to CICE which is driven by NCEP/NCAR atmospheric forcing. Navegante, Those are anomaly plots, or difference from the long term mean. Where they are white the difference from the long term mean is too small to display.
Toggle Commented Jun 15, 2015 on Melt Pond May 2015 at Arctic Sea Ice
Thanks for that David, That's two low and one high put in for the SIPN. Two of us have ideas we're testing using prediction. Nightvid is testing an approach using snow cover. I'm testing April volume as the driver of the extent decline.
Neil T, My prediction is in terms of monthly extent for September, not the 5 day average. From the SIPN Guidelines: Point number 4 reads. "4.*September monthly average projection (extent in million square kilometers). To be consistent with the validating sea ice extent index from NSIDC, if possible please first compute the average concentration for the month and then compute the extent as the sum of area of all cells > 15%." The monthly extent is available here: And September is available here:
A Team, I've fully read Carmac et al a few times (been on my phone for ages). That it is entitled 'towards' is apt, it doesn't give a clear answer to the role of ocean heat in sea ice loss. That is not to say it is of no use - I have read it several times and I found it very useful. Coming from a conference involving the leading experts a few years ago, it the MUST READ paper for everybody on the forum and reading Neven's blog or mine. As for summarising it, I can only refer people to the abstract. The onwards to read the paper itself. Notably there is only one reference to PIOMAS. Notwithstanding the concentration on other ocean heat sources I still consider that Lindsay & Zhang have accurately summed up the reason for the 1995 to 2004 PIOMAS volume loss in their 2004 paper - this being ice/ocean albedo feedback. That this volume loss in the PIOMAS model correctly reflects the dominant processes at work in the 'real world' and that the initiation and maintenance of ice/ocean albedo feedback is driven by AGW. Now, a decade on, I think it would be a valuable addition to see Lindsay & Zhang 2004 revisited and updated.
Toggle Commented Jun 10, 2015 on What it's all about at Arctic Sea Ice
Well, after several failed attempts my submission has not been thrown back from the Arcus email address, so it must have gone in. And I didn't need to bother Betsy. Nightvid is 3.26M km^2, based on snow cover. I have put in 5.15 million km^2 +/- 0.64 million km^2, or 5.79 to 4.51M km^2, based on April PIOMAS volume. Rob Dekker has yet to declare. David Rennie has yet to declare.
Bill, I think it is generally for the monthly average. A lot of the work is based on GCMs and due to internal variability within the model runs daily isn't very helpful.
Toggle Commented Jun 9, 2015 on What it's all about at Arctic Sea Ice
Neil, SIPN uses the NSIDC September average.
Thanks Rob, glad to see it was a useful perspective.
Last night my attempt to submit was rejected twice. I will have to try again tonight.
Osteopop, Boring. "Show us the proof." 1) Read Working Group 1, The scientific basis. 2) Read the references of Working Group 1, The scientific basis. 3) Do so with an open mind. 4) er... 5) that's it.
Wayne, I've just scanned it very quickly. The Results section suggests to me that the new design exhibits substantial melt due to solar heating. But this might be due to deployment in a melt pond. It is unclear whether the other IMB referred to is a traditional type with a thin thermistor string. In terms of the thin string of thermistors. If the string is substantially above zero due to solar heating heat will conduct down the string and there may be small localised melt at entry to the ice. The water would have a lower albedo and would compound the problem of solar heating. It would also lower the level at which heat flux down the thermistor starts to penetrate the temperature gradient within the ice. It's tricky, but on the face of it I am not convinced about the new design - its larger surface area suggests more potential for warming and heat flux into the fitting hole than a thin string of thermistors. Now I am reminded about why I looked at the data from these buoys about two years ago and decided I wasn't convinced it was very useful to me.
Wayne, "not my conclusion, but from the paper linked by Jim" This paper? Can you give me a string I can use to find the relevant part? I'm too busy to read the whole paper. The string shown in figure 1 will cause a very limted effect, the question regards the new system (fig 2) is much more complex! I should point out - the lab I manage does temperature calibration. When I agree with Bill I do so with practical knowledge of similar problems in getting the best precision from baths, and zero point cells.