New paper by Polyakov, Kwok and Walsh

A new paper by a few very well-known sea ice experts called Recent changes of arctic multiyear sea-ice coverage and the likely causes has appeared as an early online release, a "preliminary PDF of the author-produced manuscript that has been peer-reviewed and accepted for publication" in the Bulletin of the American Meteorological Society.

I don't have the time right now to go through this paper, but I'm putting this post up so the finer points and implications of this paper can be discussed.

Figure 1. Satellite-based Arctic Ocean multiyear ice (MYI) coverage. Composite time series shows MYI area on January 1 each year. Maps show fraction (part of a unit) of MYI. Adapted from Kwok and Untersteiner (2011).

From the paper's conclusion:

This article addresses probable causes of the observed reduction of the Arctic Ocean's coverage of MYI over that past decade. There is evidence of the increasingly important role of atmospheric thermodynamic forcing in shaping recent changes of the Arctic MYI. In addition to direct MYI melt due to high-latitude warming, the impact of enhanced upper ocean solar heating through numerous leads in decaying Arctic ice cover and consequent ice bottom melting has resulted in an accelerated rate of sea-ice retreat via a positive ice-albedo feedback mechanism. The pan-Arctic role of this feedback is yet to be quantified. Analysis of satellite ice motion suggests that the role of ice export through straits connecting the Arctic Ocean with sub-polar basins may be elusive. This situation probably differs from the situation that existed in the early to mid-1990s, when enhanced ice export through Fram Strait was caused by anomalous winds associated with the positive Arctic Oscillation phase. The possible long-lasting impact of anomalous winds such as those in 2004–05 or 2007 (especially when superimposed on a warming trend) on the state of MYI should not be ruled out. An intriguing feature of the scenario described here is the potential contribution of oceanic thermodynamic forcing to the recent changes of the high-latitude MYI coverage. Available observations suggest a thermodynamic coupling between the heat of the ocean interior and the sea ice. In the Canadian Basin, the impact of Pacific water warmth has been recently documented. While vertical AW heat fluxes are negligible in the Canadian Basin, turbulent mixing may be strong enough in the western Nansen Basin to produce a sizeable effect of AW heat on sea ice. In the eastern Eurasian Basin, double diffusion provides an important alternative to weak turbulent mixing for upward AW heat transport. However, this contribution to sea-ice loss remains uncertain pending new field experiments that will provide estimates of upward AW heat fluxes.

The fact that the rate of MYI recovery observed in recent years shows a delay relative to thermodynamic forcing indicates that MYI is resistant to recovery. However, the relative roles of dynamic and thermodynamic factors in recent changes of the Arctic MYI cover remains to be determined. Quantifying these roles is a high priority if we are to develop reliable forecasts of the future state of Arctic ice coverage.

Comments

[Artful Dodger]

We have seen clear examples in 2010/11 of the role MYI plays in resisting Summer melt. Sea Ice in the East Siberian Sea has gone through the wringer, with nearly all first-year ice melting out completely, and only some MYI remaining at the end of the season.

This illustrates how much more vulnerable first-year sea is to melt vs MYI: it has a lower albedo (0.6 vs 0.8 fraction) and a lower melting point (~1.8 C vs ~0.0 C).

Once the last of the MYI is gone (either by melting or advection), it will be much, much more likely that the entire Arctic ocean will melt out again the following year. It's just thermodynamics.

[William Crump]

I am not certain your assessment of the vulnerability of first year ice is correct and I would not use the data for just one year to support a conclusion.

From the charts it appears that the oldest and thickest ice has declined more than any other type of ice. First year ice has replaced this ice in some areas. The graph from the October 4, 2010 NSIDC report shows multi-year ice melting out faster than first year ice.

http://nsidc.org/images/arcticseaicenews/20101004_Figure6.jpg

This chart indicates that about half of the ice remaining in September of 2010 was first year ice, compared to only 30% in pre-2007 years.

The abstract for a paper recently cited by Neven indicates that multi-year ice has some capacity to recover:

http://neven1.typepad.com/blog/2011/07/new-paper-from-maslanik-et-al.html

"Analysis of a satellite-derived record of sea ice age for 1980 through March 2011 shows continued net decrease in multiyear ice coverage in the Arctic Ocean, with particularly extensive loss of the oldest ice types. The fraction of total ice extent made up of multiyear sea ice in March decreased from about 75% in the mid 1980s to 45% in 2011, while the proportion of the oldest ice declined from 50% of the multiyear ice pack to 10%. These losses in the oldest ice now extend into the central Arctic Ocean and adjacent to the Canadian Archipelago; areas where the ice cover was relatively stable prior to 2007 and where long-term survival of sea ice through summer is considered to be most likely. Following record-minimum multiyear ice coverage in summer 2008, the total multiyear ice extent has increased to amounts consistent with the negative trend from 2001–2006, with an increasing proportion of older ice types. This implies some ability for the ice pack to recover from extreme conditions. This recovery has been weakest in the Beaufort Sea and Canada Basin though, with multiyear ice coverage decreasing by 83% from 2002 to 2009 in the Canada Basin, and with more multiyear ice extent now lost in the Pacific sector than elsewhere in the Arctic Ocean."

Your statement below is not supported by observations of the Arctic Basin ice where first year ice remains in spite of massive losses of multi-year ice:

"Once the last of the MYI is gone (either by melting or advection), it will be much, much more likely that the entire Arctic ocean will melt out again the following year. It's just thermodynamics."

While the factors you cite make a logical and intuitive conclusion, they are not supported by observations in the Arctic Basin. After the severe decline of multi-year ice in 2010 - please see the October 4, 2010 description of multi-year ice decline - plenty of first year ice has survived in 2011.

I suspect the physics of ice melt and ice transport are more complex than saying the loss of multi-year ice alone will result in an entire melt out. Yes I can see you said "much more likely", but the implication of your comment is that first year ice can not survive without the presence of multi-year ice and observations do not appear to be supporting this.

I have not found any data on the rate of decline of thickness of first year ice that shows it is declining at a rate fast enough to melt out next year or in the next five years. Do you have any information on this?

The PIOMAS volume decline may primarily reflect the loss of the thick multi-year ice and may overstate the decline in the thickness of first year ice. The PIOMAS volume decline rate may flatted out in future years as there is less of the thick multi-year ice remaining to contribute to a volume decline.

The physics of why the melt may slow were provided in a recent paper that indicated that as the ice thins, more heat will be released from the ocean to the atmosphere and the heat will leave the system to outer space and that this will operate as a negative feedback that will slow ice decline.

While I am certain there will be an "ice free" day some time in the future, I do not think it will occur on the time scale you envision.

[Peter Ellis]

William: I do see the argument you're making about first year ice in the central basin. Where I think this falls down is in not accounting for the different forms of melting: top melt and bottom melt.

Top melt is driven by solar insolation and occurs across the entire pack. Lower latitudes receive more sun for longer, and thus melt more. The centre of the pack has a shorter top melt season and a lower angle of incidence, meaning it is more resistant to top melt. A given slab of ice might lose 80cm or more to top melt over the course of the summer at low latitudes, but only 40cm or so in the centre of the basin. Given that even first year ice is thicker than this, you might conclude that the centre of the basin will never melt out. Moreover, year on year, the average thickness of first-year ice at the pole would show no change. This is why you say the Pole won't melt out: and you'd be right, if top melt were the only source of melt.

However, there is also bottom melt, from two causes: 1) introgression of warm currents from other regions of the world ocean, and 2) solar warming of exposed waters that then melts adjacent ice (the ice/albedo feedback). Both of these factors operate almost exclusively at the fringes of the pack. As the warm waters, from whatever source, move under the pack, they are cooled by the ice above: their energy is used to melt the ice. By the time the warm waters penetrate more than even a few kilometres from the ice edge, they cannot cause much further melting. Thus, bottom melt works "from the outside in". Hence the analogy of sharpening a pencil - you start at one end and work your way to the other, rather than reducing the thickness of the whole length of the pencil at once.

This then is what will lead to the progressive loss of the Arctic ice. Year on year, as extent drops, the "bottom melt zone" moves ever inwards. At some point, we will reach the stage where the intruding warm waters reach the central basin without having spent all their energy before they get there. At that point, then the first-year ice thickness even at the Pole will start to drop, and soon thereafter it will be gone.

All climate models predict the complete loss of Arctic summer ice: the only difference is how fast. Those that explicitly model warm ocean incursions (e.g. Maslowski, PIOMAS) predict more rapid loss.

This latest paper backs this up 100%, explicitly attributing the majority of the recent drop in ice coverage to warming waters entering the Arctic. They state that the remaining ice more or less overlies the deeper central region of the Arctic Ocean, suggesting an important role for oceanic currents in dictating melt progress.

The Tietsche et al paper also shows it, though not as clearly. Leaving aside the artificial perturbations they introduced, look at the overall shape of the ice decline in their Figure 1.
http://www.agu.org/pubs/crossref/2011/2010GL045698.shtml

You have the long-term level at around 7 million square kilometres. Then a more or less linear drop to ~4.5 million square kilometres, and a brief plateau. This represents the area of the underlying deep basin, and the shape of the 2007-2011 minima that approximately overlie it.

However, the plateau is short-lived, and once the 4.5 million barrier is breached, there is a rapid collapse to around 2 million within a decade or so. It's that collapse we now on the brink of - presumably the remaining 2 million is left jammed up against the North Canadian / Greenland coastline. Then, after a second, more substantial plateau, there is a final collapse to a fully seasonal state.

All the models are in agreement. All the evidence is pointing the same way. The only discrepance is whether the time frame for it is 10 years or 50 - and the worst predictions are those given by the models that best capture the underlying physical dynamics of warm water incursion from outside the Arctic basin.

[Chris Reynolds]

Excellent and detailed Arctic bathymetry maps available here. The correlation of the abyssal area with the general pattern of recent Arctic ice melt is clear.

Peter,
Regards the rapid drop in Tietsche et al. Check out this paper, figure 1. i.e. Wang & Overland 2010, "A sea ice free summer Arctic within 30 years?"

The authors state that many model projections show a rapid drop once they reach around 4.6M km^2, NSIDC extent 4.33M this year. with regards figure 1 of Wang & Overland, as linked above, this is the line on all 6 panels. That paper is one of the reasons I'm saying next decade at the earliest, and like them I count less than 1M km^2 as virtually sea-ice free. If we hit that this decade you'll get no argument from me - I'll be wrong.

I'm not so sure the Polyakov paper supports that inflowing ocean heat fluxes act 'almost exclusively' at the edge of the pack. The paper states:

Double-diffusive heat fluxes across several diffusive layers occupying the 150–250m depth range and overlying the AW core from the eastern Eurasian Basin are ~8 W/m2 (Polyakov et al. 2011). These fluxes provide a means for transferring AW heat upward over more than a hundred meter depth range towards the upper halocline.

I get the impression that's within the central pack. Although Eastern Eurasian Basin may be more coastal than I appreciate.

Neven,
Thanks for the heads-up regards this paper, it's been an interesting read.

[Neven]

You're welcome, Chris, and remember: you're also/still welcome to post your interesting discussion of papers that have to do with the Arctic sea ice here (or at least drop a link somewhere). :-)

[Kevin O'Neill]

The IPCC AR4 Global Circulation Models consistently understated arctic sea ice loss. It should not be possible for an amateur armed with a copy of Excel to more accurately predict sea ice extent than software designed by experts running on the latest supercomputers. Yet that is precisely where we are today. With this in mind, any conclusions based on these models has to be taken with a grain of salt.

The bias exhibited by the GCMs can only be due, in general terms, to either

1. Overstating negative feedbacks,
2. Understating positive feedbacks,
3. Incorrect forcings, or
4. A combination of 1, 2, and 3.

One area that has been investigated and addressed is cloud formation over newly open water, see The Boundary Layer Response to Recent Arctic Sea Ice Loss and Implications for High-Latitude Climate Feedbacks. Another area that is being addressed is sea ice mechanics and kinematics, see A new modeling framework for sea-ice mechanics based on elasto-brittle rheology and IPCC climate models do not capture Arctic sea ice drift acceleration: Consequences in terms of projected sea ice thinning and decline

In the meantime, the arctic downward spiral continues. If you've read much about arctic sea ice you've probably run across the general rule that first year ice is 2m thick. Except that in 2009 it was measured at 1.7m, in 2010 that dropped to 1.6m, and this spring it was measured at 1.4m.

Some people are looking for a tipping point. Other people deny that a tipping point exists or can exist. What seems clear is that the last equilibrium state in the arctic was probably the early 1950s. It was then that the downward spiral began and, if anything, it has only accelerated in recent decades.

In this sense the tipping point has already occurred. What we're looking for now is the new equilibrium point. Will it be an arctic free of ice year-round? Will it be a seasonally ice-free arctic? Or will it be an arctic that falls some measure shy of seasonally ice-free? And of equal interest, how long will it take to reach the new equilibrium?

As an amateur, arctic, arm-chair climatologist I've read dozens - if not hundreds - of peer-reviewed papers in the last 18 months. What I've learned is there's always MORE to learn. Forget answers - I'd just like to know what the right questions are :)

That said, I think it's important to consider 2007 not as a 'perfect storm' or an outlier. 2007 ushered in a new regime; the climate changed. We will not likely see the sea ice extent, area, or volume of 2006 again in our lifetimes. 5 short years ago, but it's ancient history. I'm not sure if that qualifies as another tipping point, but if not it's a distinction without a difference.

[Artful Dodger]

Kevin O'Neill | September 20, 2011 at 04:37

Well-reasoned comment, Kevin. Compliments! I especially appreciate your links to relevant papers.

Have you read Eisenman and Wettlauferb (2009)?

Nonlinear threshold behavior during the loss of Arctic sea ice

They offer answers to several of your questions with their thorough and robust modeling effort:

• sea ice equilibrium occurs within 15 years of a step-change in climate forcings (see the SI Appendix, Fig. S2 (c) on page 7)
• Under a moderate warming (ΔF0 = 15 Wm−2), modeled sea-ice thickness varies seasonally between 0.9 and 2.2 m
• Further warming (ΔF0 = 20 Wm−2) causes the September ice cover to disappear, and the system undergoes a smooth transition to seasonally ice-free conditions.
• When the model is further warmed (ΔF0 = 23 Wm−2), a saddle-node bifurcation occurs, and the wintertime sea ice cover abruptly disappears in an irreversible process.
• see Fig. 3. Bifurcation diagram for the full nonlinear model

This is really a landmark paper. Here is Google Scholar's list of other papers that cite it. As my time allows this Winter, I plan on writing a guest post on this topic here on the Arctic Sea Ice blog.

Cheers,
Lodger

[Kevin O'Neill]

Lodger, yes, I had read the Eisenman & Wettfaulerb paper. I found it interesting, but the model it uses is a 'dumbed down' version of the GCMs. They caveat the results rather broadly:

The theoretical treatment presented here is constructed to facilitate simple conceptual interpretation, and to this end many processes have been neglected. Factors including possible sea ice-cloud feedbacks, the dependence of sea ice surface albedo on snow and melt pond coverage, ocean heat flux convergence feedbacks, changes in wind-driven ice dynamics, and changes in ice rheology in a thinning ice cover could potentially lead to other bifurcation thresholds or smooth out the threshold investigated here ...

I fully expect the next generation of models - those used for IPCC AR5 - to incorporate changes to account for these deficiencies. Perhaps then we'll see model output that more accurately reflects reality.

[RunInCircles]

Kevin & Lodger
I keep trying to figure out how relavant some of the papers written are to actual Arctic conditions. I keep reading how with thinner ice cover more freezing is expected and this counter balances the ice loss and stabilizes the ice cover. So then I go to buoy 2010H. Last October ice 115cm. Growth over the winter 125 cm to 240cm. Ice loss by 8/20 150cm down to 90cm. This buoy is at 83.5N so it is not even close to the ice edge. Do either of you know at what starting thickness winter growth catches up to summer loss? I have not seen any recent buoy data where the ice growth is exceeding the ice loss but perhaps this is because these instruments are placed on thicker ice to start with. Right now if the average loss of thickness per year is 25 cm Half of all the ice you see right now in every measure will be gone in only 3 years. I don't see any slowing in the loss rates that would indicate this negative feedback is kicking in. Right now I don't see any way that we won't have 50% less ice in just 3-5 short years.

[William Crump]

Peter Ellis:

Thank you for the detailed information on top melt and bottom melt. I have seen other sources that indicate bottom melt is more significant than top melt.

Just so my point is not understood, I believe the Central Arctic Basin will reach an "ice free" day, I just do not see this happening in the next five to ten years, but the day will most certainly come.

Some of the data I have been citing might suggest that the Central Arctic Basin will not melt out, but I do not believe this. Although extent/area are holding up, I suspect the thickness of first year ice is decreasing, but data is nearly non-existent, and I just suspect the thickness is not declining fast enough to produce an "ice free" Arctic by 2019.

Because of the deteriorated condition of the ice pack, my guess is that there will be some rapid drops followed by partial rebounds/new temporary equilibrium points, but eventually an "ice free" day will occur.

[Peter Ellis]

William: Yes indeed - the significance of bottom melt is very variable depending where you're measuring it. NSIDC covered it a bit in their August update.
http://nsidc.org/arcticseaicenews/2011/081611.html

Crucial image is here:
http://nsidc.org/images/arcticseaicenews/20110816_Figure4.png

The buoys in the central Arctic had essentially no bottom melt by mid August, while those at the edge of the pack were showing significant bottom melt.

Even bearing in mind that the bottom melt season predominantly runs from early August to mid September, the pattern is clear: it works from the outside in. This year, by the end of July, there was open water up to around the 80th parallel, and bottom melt thus extended some way north of that during August and September. As the edge retreats further in years to come, bottom melt will come in to play in the central pack too.

[Peter Ellis]

Another paper showing the ratio of top/bottom melt for the whole of 2008. Overall proportions are very different to the NSIDC figure, in part because the latter only included the very start of the bottom melt season, but perhaps 2008 also had particularly large influxes of warm water from other regions?

However, the spatial pattern is still clear - in the central Arctic, bottom melt was around the same as top melt: around the fringes it was more than double the top melt.

http://www.joss.ucar.edu/events/2009/aon/reports/richter-menge_jackie.pdf

[Simon]

Slightly OT: Eisenman and Wettlauferb have a nice approach to graphing the "negative ice" that sometimes shows up in discussions of trend and extrapolation.

[Bob Wallace]

Yes, I am obsessing over volume.

Take a look at this graph...

PIOMAS data taken from Larry's volume graph. Last bar covers only two years.

Over the 32 years covered by this time span year-to-year volume increased only eight times. In the last ten years volume increased only once and that was following the 2007 'big melt'.

From 2000-2004 volume fell 128,000 km3, from 2005-2009 volume fell 308,000 km3 and during the last two years an additional 339,000 km3 was lost.

Volume loss is accelerating and if first year ice is thinning then I would suspect CA ice to come under significant attack during the next melt seasons.

[RunInCircles]

Peter
Thank you for the 2008 data. 1 correction the NSIDC chart was only through July 20 not August. Most of the bottom melt occurs after July 20th every year except at the very edge of the ice. The ice bouy chart on Nevens graph page contains a wealth of data showing melt rates this year.

[Andrew Xnn]

Although physic based models are important, they are far from perfect and must of necessity make simplifying assumptions. In addition, despite their complexity, they are fully capable of containing fundamental errors.

As such, we are left with reviewing and trending measurement data while taking care to not cherry pick. At the end of each season, whether it be freeze or melt, the prime question is if it reinforces the long term trend or not.

[me.yahoo.com/a/nSjChi4X3vr8X3DRw93GkY1.cerja.8nvWk-]

Eisenman and Wettlauferb (2009)?

Nonlinear threshold behavior during the loss of Arctic sea ice

Thanks Lodger, v interesting, it looks very similar to the bifurcations I studied for my thesis way back (Chemical Kinetics). In that case the transition to the upper state was oscillatory which could of course also be the case here. In my case the temperature required to jump down was much lower that that required to jump up which appears to be the case here.

Phil.

[adelady]

"...shows a delay relative to thermodynamic forcing indicates that MYI is resistant to recovery..."

I've just realised something. We've been talking all the time about melting. Top, bottom, early, late, edge, central.

The loss of volume, esp in the central areas, could be based not so much on melting, but on 'failure' of freezing in the first place. The waters beneath the ice in seasons other than high summer may not be able to melt much/any ice, but the flows being consistently warmer (less freezing) than 20 years ago means that the ice that does form is not consolidated as it was in the past, nor is 1st & 2nd year ice forming as robustly as previously. The image of ice breaking up rather than piling up comes to mind.

All this prompted by my kitchen. A domestic refrigerator certainly freezes food and water. But it's simply not powerful enough to be as fast or as effective as a commercial freezer. Nor is the result as resistant to temperature fluctuations as food or ice formed under strong freezing conditions.

I'm sure I'll think of something 2 hours from now that'll make the analogy invalid, but it struck me quite forcibly when I first thought of it.

[RunInCircles]

Adelady
You are of course correct. It is the difference between the winter freeze thickness and the summer melt that is all important at this stage. From very little data I've got an estimate of almost 25 cm less ice now than last year. Does anybody know what the North Pole Web cam is showing? It just cleared a little bit after being totally black and the 13:33 picture appears to have blue in it. With an internal temperature of minus 12.5 degrees this seems unlikely to be water on the ice. Looking for insight! Thanks in advance.

[RunInCircles]

Neven
Could you put up your capie graph on the web page?

[Chris Biscan]

Temperatures this week are going to blow records in Canada by the Hudson Bay away between 10-30F with places 30-40F above normal.

this will also help set record warm SSTs in the Hudson Bay.

with 850s 20-24C above normal for 3 days up there.

That is insane

[Neven]

RunInCircles, I'm going to update the Daily Graphs page soon. I'll put it up there and update it every month or so (unfortunately I can't write a script for it to happen automatically).