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Anu

@ Phil263 | September 22, 2010 at 00:33

Actually the equinox is 11:09 pm EDT on September 22, 2010.
http://www.erh.noaa.gov/box/equinox.html
Same as 3:09 am UTC on September 23, 2010.
http://en.wikipedia.org/wiki/Equinox

I also doubt we'll see a new minimum, but I have enough popcorn left for one final surprise. Things will be definite by next week, that's soon enough for me.

Anu

When Zhang and Lindsay update their animation so that the hindcast portion includes Sep 15, 2010 you'll have your thickness distribution data. I expect they will be a close fit to the Aug 8 forecast.

Posted by: Artful Dodger | September 21, 2010 at 23:58

Yes, I suppose it will be a pretty close fit.
http://img39.imageshack.us/img39/1010/piomassept142010.png
(sorry, Quicktime messes up the color table a bit, but it's readable)

I find the margin thickness interesting - 12.5 to 25 cm, then 25 to 37.5 cm, then 37.5 to 50 cm thick, the warm surrounding waters not quite able to completely melt a band of about 100 - 300 km wide (compared to Banks Island length of 380 km) all along the Beaufort, Chukchi and East Siberian Seas.

Also, the entire ice pack seems to get thicker the farther it gets away from the warm water, making for a triangle wedge shape - kinda like this:

The crust is up against northern Greenland and the Canadian archipelago, and the margins are a bit thinner, like overflowing cheese...

The Arctic death spiral is like nibbling away at the pizza slice, summer after summer, saving the crust for last.

Artful Dodger

Let's return to the analogy of the loss of Arctic Sea Ice to the discharge of a Battery now that we have the Sep 15 volume anomaly from PIOMAS. If the average minimum volume is 14.6 K km^3 and Sep 2010's volume is 3.9 K km^3, then we have lost about 73.3 % of baseline Sea Ice Volume.

Let's plot that percentage on a graph of potential Rates-of-Loss curves, modeled after a battery discharge curve:

Proposed Volumetric Melt Curve

The most pronounced characteristic of this discharge curve model is that it remains very flat until approx. 80% of energy is discharged, then begins a rapid fall to zero. Could battery discharge be a model for the loss of Arctic Sea Ice?


H Barnard

21 Sept IJIS extent 4,901,406 (an increase of 23,125 km2). Does that mean that curtain is falling?

Werther

Neven, Anu
As I understood, Piomass is based on a model, using some random real-time thickness info and a variety of climate/weather parameters. Maybe that is why the shape of the 14 september graph doesn’t match with the CT areas of high/low concentration. The Piomass graph triangle is directed to Severnaya Zemlya, where concentration was quite ‘mazed’ on CT. OTOH it seems weak in the direction of the Beaufort Sea, where concentration always remained high to 75 degrees N.
Overall, the Piomass graph shows that our assumption of +/1 4000 km³ volume isn’t far from reality. It may even be less when the high concentration CT graph and the Piomass graph would be analysed together. That area, some 3.5 mk², could on average be less thick than 1.2 m. Anyway, it’s no use anymore to discuss extent as if it were the leading canary. It’s the volume, and it’s going, going…

me.yahoo.com/a/Xs1LkmQn0_XQko.cH1qfXW.Bvo0cvQ--

As an amateur, I know that tropical storms/depressions etc bring some of their own temperatures and moisture with them. Any thoughts on Igor affecting the ice? I guess warm temps/water bring some melting but equally fresh moisture plus existing low temps bring snow and ice. Waves... not sure: they break up ice but seems that spray would freeze quicker. Any idea how the winds/currents will be affected? Or will nothing in particular happen since Igor is too far south and in the wrong location?

dorlomin

Neven
However, I do have a hunch that freeze-up could be slow. Maybe CT area anomaly could deliver a surprise, like dipping under 2 million square km.
= = = = = = = = = = =
The anomaly on CT is always much greater during the Autumn than the Summer, IIRC it tends to max out in about late October early November.

FrankD

Artful Dodger said:
"Peter Ellis: Outstanding analysis, Mate! I do believe your onto something: We may have stumbled onto a metric for Melt Ponds. Now there's a testable hypothesis! I wonder how we'll use this... ;^)

FrankD: Thanks for doing this work, and for redoing it (some of my best stuff is done on the 10th try!). Seems to me that we should attempt to normalize the new statistic somewhat, so that the 'percentage' plot represents a proportion of the total ice covered with melt ponds. I'd suggest dividing (IJIS Area - CT Area) / IJIS Extent as the new statistic.

Peter or Frank: Have you thought of a name for this new Construct? Seems to me 'Top Melt' might capture the spirit and intent..."

Firstly, I totally agree - that's really well spotted, Peter. I noticed the sharp change of course, but only got as far as "Hmph, how about that...?"

Lodger, call it "Top Melt" if you want, its probably better than the acronym which for CT-IJIS delta over IJIS Extent would be something like CIDOIE. I must say, its getting a little "meta" for me, and I'm not sure I can visualise exactly what that metric would really mean. However, since I have all the data handy, I graphed it as requested:
http://img826.imageshack.us/img826/2310/ctijisdeltaoverijisexte.png

Oh, and *coff*: http://neven1.typepad.com/blog/2010/07/search-september-sea-ice-outlook-july-report.html?cid=6a0133f03a1e37970b0133f2b70d25970b#comment-6a0133f03a1e37970b0133f2b70d25970b

:-)

Peter Ellis

FrankD: I'm not sure what Lodger was after in using IJIS extent as the denominator. If the delta is due to top melt, then the obvious thing to do is simply plot CT area divided by IJIS area. That would thus give a measurement of what fraction of the "true" IJIS area is covered by melt ponds and hence not detected by the CT algorithm.

Artful Dodger

FrankD: "I'm not sure I can visualise exactly what that metric would really mean"

"Top melt" == "Effective Solar Insolation."

Notionally, it's the amount of heat the Sun actually delivers to the surface of the Sea Ice, through the Clouds, Volcanic Ash, Siberia Tundra fires, etc ... I think it'd even be affected by Black Carbon, don't you?

Peter: Yes, I totally agree with you. Use IJIS Area as the denominator, it's much more sensible.

Frank and Peter: So if this construct does measure 'top melt', don't you think they'd be a signal in the July data, while the Central Arctic was so cloudy?

Now, does anyone have an index for Arctic Cloud cover? It'd be great to know the correlation between it and 'top melt'.

Artful Dodger

CT Area Is DOWN for the period ending Sep 21, 2010.

The Decrease is -44,368 km^2 for a new SIA of 3,242,925 km^2.

As Mark Twain said, "The report of my death was an exaggeration"

BTW, PIOMAS predicted the end of the melt to occur Sep 28...

JackTaylor

For those who wish to claim the Fat Lady has sung,
we "more mature" fans of American Style Football have a Monday Night favorite
way of describing things

http://www.polk-nc.com/agw/mp3ss18.htm

If you wish to post - place on your site - blog, E-mail contact me and will send
in a ZIP file the code and instructions.

Peter Ellis

So if this construct does measure 'top melt', don't you think they'd be a signal in the July data, while the Central Arctic was so cloudy?

Search me, I'm a molecular biologist! :-)

Taking a wild stab, I'd say that once the melt ponding has occurred, changes in cloud cover don't cause the ponds to vanish. See this year's Arctic webcam for an example. Even when it clouded up - heck, even when the pond skimmed over with ice - the pond was still there, and still substantially darker than the surrounding ice.

Might explain some of the "blinking" effects in the ice concentration pictures, I guess - maybe ice, ponded ice and ponded-ice-plus-skim-ice-on-pond all show up subtly differently.

Artful Dodger

Peter: One needs to compare rates of change: If the proportion of ice covered in melt ponds is steadily increasing, we can say that "effective solar insolation" has value 'x'. Then if the rate of change in 'top melt' suddenly changes, run to the wx charts. Is it cloudier? Was there smoke from fires? Volcanic Ash, you get the idea. This data then further helps us to 'normalize' the melt rate for the season. IE: if wx conditions (the big unknown) return to normal, the melt should then be this...

David Barber would have loved you on his multi-disciplinary team. We are after all witnessing the loss of an ecosystem. BTW, do you have any software to predict the tertiary structure of a protein from it's encoding base-pair sequence? I can also accept src code... ;^)

Anu

@ Artful Dodger | September 22, 2010 at 05:19

I think one of the sigmoid functions would be a better fit - maybe the error function erf:

Inverted of course: 1 - f(x)

Fitted to the September minimum volumes, it could match the fast drop of the first "ice free" summers, then the slow fade of the residual thick ice near the Canadian Archipelago and northern Greenland that Dr. Maslowski expects to linger on for a decade or two. His essentially "ice free"summers allow for a few hundred thousand km^2 of such thick ice that gradually dies out.

Even using one of the curves to give a "best fit" match to existing volume data is no guarantee that it has predictive value - it's just a quick and dirty tool.
There's no substitute for actual high-resolution 3D Arctic sea/land/atmosphere models, and even these need boundary conditions from full Earth GCM's to predict the next decade or two.

But people have done that, and it looks at least likely that a sigmoid curve will be a pretty good description of what will happen.

L. Hamilton

It looks like NSIDC extent for 9/21 has gone down just a little bit further.

Artful Dodger

Anu: That's excellent, thanks for thinking about this. Right now, I'm still working at a conceptual level, but would like to do some modeling based on a comparable system. That's how I developed the analogy of seasonal change in Arctic Sea Ice as the charge/discharge cycles of a Battery.

The problem with using a sigmoid function is that it is most useful to predict an end-state series over time, ie: a plot of Sep minimums over the next 50 years. I'm actually interesting trying to model the loss/gain cycle itself, somewhat like this over the next 50 or 100 years.

Notice that in my "Proposed Volumetric Melt Curve" above, 2-D Sea Ice cover never gets to zero; the 'battery' is fully discharged before then. I think this would be similar to the long tail of the Sigmoid function as well. The key to the 'Battery' model would be to identify and estimate the forcings as either 'load' or 'charge'.

For example: Warm winters, lot's of snow insulating the sea ice, those are reduced 'charge' inputs to the battery. Warm Summers are increased 'load'. Ice advection through Fram Strait? that's a 'load' (or is that a SHORT?). Increased Cloudiness? Decreased load in Summer, decrease charge in Winter (warmer under Cloud). Warm Pacific inflows => load. Increasing CO2 + CH4 over time => increasing load. Solar cycles, orbital elements, ENSO, if can, can. You get the idea...

Now the total Energy in the battery is the sum of ( Mass of Ice * temp * specific heat of Sea Ice ) + ( Mass of Sea Ice * enthalpy of melt ). Add the sum of forcings to get delta-sea ice volume in a single cycle. Iterate to predict a sea ice volume time series. You can then plot Sep min predictions over time, which will likely look like the Sigmoid function.

However, I believe the Arctic will NOT enter a steady state which includes minimums always occurring in Sep. There is good evidence that during the PETM 55.8 Mya the Arctic was Ice Free year round, with average annual temps over 18 C. There are fossilized Crocodiles on Baffin Island (say, isn't there a Hurricane there today :^).

BAU (Business As Usual) looks like our likely future given our Political quagmire. This takes C02 over 800 ppm by 2100. Of course it's easy to model other CO2 senarios...

Anyway, all this should be more than a match for my PS3 Cluster!

Peter Ellis

BTW, do you have any software to predict the tertiary structure of a protein from it's encoding base-pair sequence?

Heh, if I did I'd be a lot richer! My main field is sex chromosome biology and male fertility - I'll pop up on NCBI Pubmed if anyone's interested/bored enough to search :-)

Patrice Pustavrh

Our Norvegian and Russian friends has completed the NW Passage. Comment from Borge and Thorlief says it all:
It is, unfortunately, the dramatic changes in Arctic sea ice conditions in recent years that have made this trip possible. On the time of Roald Amundsen it took five to six years to complete the same distance, due to the extremely difficult and demanding ice conditions. Now we have proven that it is possible to make the voyage in a 31-foot fibreglass sailing boat, equipped with a 10 horsepower outboard motor for emergencies. This shows how dramatic and how fast these changes are happening. The changes that we are witnessing will influence climate on a global scale, in addition to the whole range of animal life in the Arctic – especially seals and polar bears, whose lives are dependent on the sea ice.

It is our hope that our voyage will be seen as a strong, visible symbol of the scale and the speed of these changes.

More on: http://www.ousland.no/2010/09/re-completing-the-passage/

Steve Bloom

Anu, isn't Maslowski's surmise about residual thick ice near at least the Canadian Archipelago refuted by what happened this summer? It's all gone AFAIK.

Neven

There won't be an extent decrease reported tomorrow either:

Jon Torrance

Steve,

What's the basis for your "It's all gone AFAIK." in reference to "residual thick ice near at least the Canadian Archipelago"? Nothing I've seen says that the oldest and thickest surviving ice isn't mostly immediately north of the Canadian Archipelago and Greenland.

Artful Dodger

Daring analysis, Neven! What about that big arrow at the 'elbow' of the 'arm'? I think we're still losing multi-year sea ice to melt in this area (of course, gaining new ice elsewhere is irrelevant because it'll all be gone my June 2011).

Greg Wellman

While the old thick ice north of the Archipelago isn't quite as old or as thick as it was, it's still the most robust remaining. I think Steve was referring to the fact that a good fraction of the old thick stuff from 2007 rotated out to the Beaufort and East Siberian and was lost this year (and a bunch flushed south through the Archipelago this year too.) It's still the region that will average the thickest and probably survive the longest.

Agreed with whoever pointed out that the CT arctic anomaly usually reaches it's most negative sometime in Oct-Nov. Note that right now the arctic anomaly at CT is -1.6M, and the antarctic anomaly is -0.5. Yup, so much for the magic "the poles are linked such that the antarctic will make up for the arctic" theory promulgated by S. Goddard. Should be interesting to see what the global anomaly looks like for the next few months. http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/global.daily.ice.area.withtrend.jpg

Artful Dodger

Steve: Jon, Greg and Anu's Pizza Crust are correct. The thickest Sea Ice in the Arctic remains North of Greenland near the Lincoln Sea and Kap Morris Jessup. The ASAR images show that the sea ice there is broken and mobile (I plan to create an animation soon). Watch this area this Fall for ice advection.

According to the Sep 20, 2010 PIOMAS forecast, the sea ice NW of Greenland is between 2.5 to 2.6 m thick. I also note that the Sea Ice North of Ellesmere Island is now quite thin:
PIOMAS forecast Sep 20, 2010

Lord Soth

If the remaining arctic ice thickness resembles a pizza, then it must be a thin crust pizza.

On another note, The Canadian Ice Service has successfully dropped a transponder on the smaller Peterman B ice island, which has just entered Baffin Bay.

You will now be able to track it speed and path here

http://sailwx.info/shiptrack/shipposition.phtml?call=47557

At the speed it is moving, it will stay ahead of the freeze up in Baffin Bay, and may be a threat to shipping much sooner than expected.

Artful Dodger

Excellent, Lord Soth. It looks like the A'berg is averaging over 23.7 km/day VMG. Have you posted a comment over at Logicman's Blog?

Steve Bloom

I expect that the Baffin Bay freeze-up is going to be set way back by Igor. (Or since he's now extra-tropical, maybe Eye-gor is better.)

Re the thick ice, I was distinguishing between the area above the CA and the area above Greenland. I see that a bit is still shown in the former area, but the point I was trying to make is that the movement through the archipelago this year shows there's no longer much persistence there in the absence of other ice to act as a replacement supply. I think it had much more persistent characteristics at the time Maslowski made that prediction.

While we're on the subject, at a couple of points during the summer Julienne had mentioned that there was still some multi-year ice in the Beaufort. Is it now all gone, or did it move east?

Steve Bloom

Will Eye-gor also put a quick end to Mann Ice Island?

Artful Dodger

Steve: Yep, there's a little bit left in the Beaufort 'finger'. Healy cruised through the remaining Sea Ice on Sep 19th:

http://mgds.ldeo.columbia.edu/healy/reports/aloftcon/2010/20100919-1701.jpeg

Note the rotten ice and melt ponds, high air temps. SST's above t(s) melting point too:

http://www.sailwx.info/shiptrack/shipposition.phtml?call=NEPP

Steve Bloom

But not enough for PIOMAS to show, apparently (assuming that a significant mass of multi-year ice would perturb thickness somewhat). The final report on surviving multi-year should be interesting.

Artful Dodger

New Climate Progress post from NSIDC director Mark Serreze: “The volume of ice left in the Arctic likely reached the lowest ever level this month.”

adelady

I know this is all terribly exciting and there's a lot of cerebral activity in working out what's likely to happen when.

Many of you guys are part of networks of many people who travel or otherwise take an interest in these areas. May I strongly suggest that you start prodding a few who are involved in film or tourism or whatever to plan for trips from late winter, early spring onwards.

If what some of us think is happening, IS happening, we need the largest possible stock of visual records of "what the Arctic was like when grandma was a girl". Because we won't be able to go back and do it later. If we focus too much on recording the decline and fall, we won't have enough records of what the real thing was really like.

Depressing I know, but someone has to say it out loud.

dorlomin

Antarctic has fallen below -0.5km^2 on CT. Thats rather unusual.

cynicus

Anu, curve fitting is very interesting, but even if you get a (temporary) fit then you still need to explain the physics behind it. Without the explanation the curve means nothing. So if the Actic volume/extent fits the battery type curve or inverse Sigmoid the it needs to be explained why (the steep drop to 0 vs the long tail for instance).

Gareth

The Antarctic situation reflects a recent shift in the Southern Annular Mode (our equivalent of the NAO). SAM's been strongly positive over most of the SH winter, which has tended to keep the cold "bottled up" over Antarctica, thus favouring the growth of lots of sea ice. It's recently dropped into negative territory, which has allowed the polar front to meander northwards, and brought snow to southern NZ, and strong equinoctial winds.

More on annular modes here, and the current index here (though NOAA call it the AAO, just to be confusing.

JackTaylor

"strongly suggest that you start prodding a few who are involved in film or tourism or whatever to plan for trips from late winter, early spring onwards"
adelady | September 23, 2010 at 08:13

http://barneousa.com/default.aspx
Barneo Ice Camp has Arctic Tours near the North Pole in early spring.

Neven

Perhaps somebody mentioned it already, but CT global sea ice area anomaly is way, way down. Record territory, one might say.

Anu

Anu, curve fitting is very interesting, but even if you get a (temporary) fit then you still need to explain the physics behind it. Without the explanation the curve means nothing. So if the Actic volume/extent fits the battery type curve or inverse Sigmoid the it needs to be explained why (the steep drop to 0 vs the long tail for instance).

Posted by: cynicus | September 23, 2010 at 10:40

Well, I wouldn't say "means nothing", but I agree with your general point.
(e.g. if you plot your weight, day by day, over the last 3 months and notice a trend of losing about 10 pounds/month for no obvious reason, even if you don't understand medicine, you better try to find somebody who does... the curve means "something is wrong")

But the curve fitting here is basically a parlor game - like preferring Tamino's quadratic fit over NSIDC's linear fit, to better guess what the minimum extent will be this summer (and now, after CryoSat-2 data comes out, people will make predictions of 2011 summer ice melt next Spring).

The real physics is in the computer models - I prefer Dr. Maslowski's approach, as I've said previously in this blog (there's a Search tool). He uses a higher resolution (regional) model than most GCM's (General Circulation Models), because he believes a coarser resolution misses important coastal currents and ocean eddies that bring heat from warmer, exposed waters to under the sea ice, causing bottom melt. He focuses most on the growing ocean heat and the growing volume melt trend, whereas other researchers focus more on atmospheric conditions - warm winds from the south melting sea ice from above, etc... NSIDC seems to prefer researching these factors (every research group has their preferences). Although the warming planet does affect wind patterns, I think the ocean warming signal is much clearer, and a better explanation for Arctic sea ice volume shrinking summer after summer.

then you still need to explain the physics behind it.
Certainly someone needs to explain the physics behind those curves - but not me. I haven't done serious physics in many, many years :-)

The long tail in the volume curve is supposed to be the stubborn, thick ice hugging the coast of the Canadian archipelago and north Greenland. It is not the curves that suggest this, it is the long computer runs of the the regional Arctic sea-ice/atmosphere/land models that Dr. Maslowski has been working on for many years.

Other models will have different detailed predictions, but most of them are becoming increasingly "optimistic" over the last decade. The "skeptics" are quite right that computer models are not the same as reality - sometimes early models miss some subtle real world process, and things are much worse than at first predicted.

cynicus

Anu, thanks :-)

I agree completely with noticing "something is wrong" in the trends, but my response was intended for the Battery vs Sigmoid discussion. Without a proper explanation there is really nothing more to those discussions then to conclude that one or the other function fits better, it doesn't explain anything and it doesn't really gives us the answers we need.

The discussion was a little bit (a very little bit!) like the other side of the mirror plotting a polynomial fit to x-years of temperature in order to be able to say that there will be global cooling the next 30 years. That's what I was trying to say: just curve fitting doesn't mean anything and has no real predictive power unless you support it with real physics.

Although you claim not to have done serious physics for a long time, now you do present a possible physical mechanism to support your Sigmoid claim and that's what I was after ;-) Thank you!

I have a hard time thinking about the way the old ice along Greenland an the CA Archipelago will disappear. Multiple scenarios cross my mind: transport of most of it out of the Basin in one or two years would support Lodger's battery curve, while slow in-situ (bottom?) melt, transport and replacement by new ice would support yours. Somehow I can see both happening, but I'm not nearly as qualified to judge it as most of you here, let alone the professional specialists.

Kevin McKinney

Interesting comments about Maslowski's research. In general, from everything I've read on the topic, regional forecasting is much more challenging than at a global level. I believe that improving regional forecasts generally is presently a strong research focus, for some of the reasons suggested by your comments.

I share cynicus's humility--one of my outstanding credentials to comment here is that I used to hang out with meteorologists a lot about 30 years ago! (My father-in-law at the time was a senior official with Canada's then-Atmosphere & Environment Service. I wonder if playing badminton with the pros trumps actually "playing a pro on TV," as the current cliche has it.)

A lot of those met guys had their own 'top ten' list of worst forecasts they'd made; I seem to recall that one list was headed by missing the daily max temp for Hurst, Ontario by about 30 degrees C--and missing the snowfall completely. . . timing the movement of a frontal boundary, combined with local 'microclimate' effects--it wasn't that the whole forecast map was completely wrong.

And of course, we saw the "law of small numbers" this season. Conditions in July strongly affected the eventual minimum; it's a noisy system. And would it be fair to say that the effects of weather in the summer of 2007 are still reverberating in the system? The declining trend didn't start then, and can't be blamed--as some denialists I've encountered have done--on a fluky "wind-driven" event. Yet the extremely high ice advection that summer did do a lot to deal a death-blow to the multi-year ice, it seems to me.

I suppose that's why my intuition pictures a surprisingly quick finale for the thick ice north of Greenland. We'll bumble along, losing a bit more on average, and then the stars will align and we'll get a 2- or 3-sigma loss event. And then it'll be ragged shards, random floes and bits of landfast ice in sheltered inlets, and not much else one summer.

Of course, we could also get the opposite--a year in which the most favorable possible conditions for ice conservation persist more or less throughout the melt season. And if so, we'll get a lot of triumphalist crowing about "recovery"--but it'll just be a slight delay of the inevitable. And then the parlor game will be about the effects--Arctic coastal erosion, adaptation (or lack thereof) of biological populations to habitat loss/change, meteorological effects, permafrost/hydrate melting, and feedback effects to the climate at hemispheric and global scales.

And call me an optimist, but I do think we'll lose most climate denialism at about that point--though there will be "radical adaptationists" arguing that we need to burn every last bit of fossil fuel to preserve human well-being in the face of severe climate challenges that, they will claim, are "inevitable."

me.yahoo.com/a/Xs1LkmQn0_XQko.cH1qfXW.Bvo0cvQ--

I think the denialist crowd has already started to hedge their bets. They know the ice is going. I think for sites like WUWT, the reason is about credibility: the site generates revenue and they want to be able to maintain a record of being right no matter the future holds. For others, I think the reasoning is split into two camps: those who genuinely emotionally want this to not be true and those who are well paid to put out propaganda.

The shift is/will be to headlines like: Ice Free Arctic is Good for the Economy, Nature is Returning to Normal, etc.. No one will mention that it's not the position but the velocity that is the problem, as in a pendulum that returns to zero doesn't stop at zero but goes well past it. An incremental approach to a melted arctic might not signify anything other than dead walruses and polar bears. An express train that doesn't stop there is scary: how hot will it get, how many people will die, where wil the future end up?

The correct name for these people is not denialists, IMHO it should be something like Big Oil Appeasers, or Global Warming Ostriches, i,e, it should be something that reflects the cowardice of their stand. The need is to take away the image that the denialists give themselves of being strong independent thinkers (in opposition to the stupid alarmists).

Jon Torrance

Formality though it is, looking at the PIPS ice displacement forecasts for today and tomorrow I'm now prepared to say I'm certain we've seen the JAXA extent minimum already, regardless of any change in the winds in the week or so to come.

adelady

Kevin, "..my intuition pictures a surprisingly quick finale for the thick ice north of Greenland. We'll bumble along, losing a bit more on average, and then the stars will align..."

I think that the year we have the next big el Nino will be the signal for the ice disappearing in the way you suggest. 6, 12, 18 months later a big flush of very warm water will flood through from the Pacific, and there won't be any resistance to it going straight across and scattering whatever ice might be clinging on to Greenland.

"Ragged shards, random floes and bits of landfast ice" cowering in a few inlets like good citizens hiding themselves from a rampaging crowd of hooligans.

And then it will be over.

Artful Dodger

The 'battery discharge' curve relates 2-dimensional (spatial) coverage of the sea ice to its the 3-dimensional volume. Time is NOT plotted on this graph. It is not a time series.

The graph does demonstrate how 2-D coverage can remain quite stable even while 3-D volume decreases steadily. The key predictive attribute of the model is that there is a tipping point in volume related to a precipitous decrease in 2-D coverage.

cynicus

Thanks Lodger for explaing the bit that eluded me. I get what you're trying to say, we even saw this happening this spring with the late extent peak of very thing ice: it melted quickly. The Arctic will still freeze over almost completely in winter for a long time, but if the ice is thin enough then it will totally melt away the next summer too. Right?

Thanks for your interesting comments this past season.

Peter Ellis

The battery model implicitly assumes uniform thickness across the Arctic, and consistent rate of loss across the Arctic. In that case you have a stored resource which sustains a given rate of loss until it runs out and suddenly all vanishes.

Unfortunately both of those assumptions are fundamentally unphysical. In addition to the dodgy assumptions, the battery model seems to contradict the data: it predicts little to no change in extent until the vanishing point, which is not what we're seeing, as the last few years amply prove.

A more physical assumption would be to assume a variable distribution of "meltability" across the ice pack - i.e. the fringes are vulnerable, the core is more robust, and the fringe around Greenland is particularly robust. Given that "meltability" depends on multiple interacting factors (e.g. thickness, salinity, latitude, local weather, local geography...), we can appeal to the central limit theorem and assume the distribution will approximate to a normal or log-normal distribution. Both of those would lead to a sigmoid curve.

In practice, Arctic amplification, particularly ice-albedo feedback means that the amount of excess energy input will increase each year. Thus, my personal prediction is for some kind of asymmetric sigmoid curve, with the second half being steeper than the first half.

The Grumbine/Wu prediction in SEARCH used a logistic curve and came very close. The prediction was slightly under the mark, either through simple random chance or because they used a symmetric curve - note that we're still on the upper half of the melt curve, so a symmetric curve will undershoot the asymmetric one I'm suggesting.

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