The acceleration of the loss of the extent of the ice is mostly because the ice has been so thin. This would explain why it has melted so much this year. By June the ice edge had pulled back to where it normally is in September... .
..The 2007 record was set when you had weather conditions which were perfect for melting. This year we didn't have those. It was mixed. So this suggests the ice has got to a point where it's so thin it doesn't matter what the weather is, it's going to melt in the summer. This could become the new normal.Julienne Stroeve.
I've been one of what has seemed at times like a minority of one in the amateur community following the loss of Arctic sea ice. My view had been that the ice was transitioning to a new pseudo-equilibrium state, one with an ice pack composed almost entirely of young ice. I now doubt that such a pseudo-equilibrium state exists, and I anticipate a rapid transition by 2020 to a virtually sea ice free state (NSIDC Extent <1M km^2), I suspect it could be much earlier than that.
The loss of volume until recently has come from thicker ice categories, as thickness is a proxy for age it can be presumed that a process has been underway removing the thick old ice from the Arctic.
Indications are that this process is now at an end.
PIOMAS volume contributions from four thickness categories of sea ice, 1978 to 2011.
This is also supported by the work of Maslanik, which shows that ice over 4 years old is imminently due to be lost from the Arctic.
I had expected that at the end of the process of removal of old sea ice a new pseudo-equilibrium would begin with a younger ice pack more prone to melting ushering in a new regime of greater volatility. Since 2010, and certainly with this year, that seems to be what has happened. However I am no longer convinced that this is a semi-stable state that implies survival of the pack in summer until well into next decade.
The PIOMAS model is the best measure of volume we have, it is well verified against past observations such as submarine and satellite measurements. Furthermore initial indications are that Cryosat 2, the new satellite system supports PIOMAS, more here. And PIOMAS shows substantial recent March volume losses, implying thickness loss.
This is supported by the PSC's own calculation of thickness, here, and by calculated thickness, here. It's worth noting that there have been similar volume losses in the past, so what is different now?
The difference is that the ice is thinner.
Here is the thickness* before the volume losses of 1981/2, a volume loss that didn't lead to a crash in area/extent. I've chosen June as this is at the beginning of the melt season before the biggest volume loss which is in July. *(PIOMAS gridded data - my presentation)
Here is the thickness before the volume losses of 2010/11.
And here is the thickness in June of 2011, 2012 gridded data should be out sometime next year.
The following two graphics are taken from this presentation (pdf) by Marika Holland on Rapid Ice Loss Events (RILEs). I mentioned March ice volume in connection with my first graphic, that was not without reason; Holland's work shows that in models March thickness (therefore volume) drops during RILEs.
The RILE is marked with the grey band, it's worth noting that current thicknesses are below that of the model above during a RILE. Why is this important? After all as can be seen from the above two graphics, both volume and thickness show large drops earlier in the 20th Century. The key issue is Open Water Formation Efficiency (OWFE).
OWFE is defined as the percentage of open water made by each cm of vertical ice melt. Back in the 20th century and before the ice was thicker, so OWFE was low (to the right of that curve). But now the ice is much thinner so the same losses of thickness during the melt season are much more able to expose open ocean.
Going back to the presentation by Holland she states:
• In most extreme case, conditions go from near-present day
to near-ice free Septembers in ~10 yrs• The transitions result from:
– A vulnerable, thin ice state: Increased OW per melt rate
– A trigger: Increased OHT (natural variability?)
– Accelerating feedbacks: Albedo change/OHT?/Clouds?
As I've shown recently the loss of volume in 2010 rivals that of 2007, here, and was driven by unique weather conditions, here. 2007 was also driven by weather, but as it turns out the weather pattern responsible, the Arctic Dipole (AD) has stuck since then due to a highly anomalous atmospheric condition, here, why remains unclear. But the Arctic Dipole is a key player that transports warm air into the Arctic basin, has a proven role in sea ice loss (here), and has been active every year since 2007 in early summer, as Overland et al show (see previous post for reference).
The June AD index from 1950 to 2012 shows how unusual recent years have been.
The June AD index from 1950 to 2012 shows how unusual recent years have been.
In the last 6 years we've had: 2007's loss of 1/4 of the sea ice area, and the start of an unusual assertion of the Arctic Dipole. Continued year-on-year volume loss (PIOMAS) with 2010's loss of volume equalling 2007, and the majority of the thickest, oldest ice off the Canadian Arctic Archipelago (CAA) being lost. The area record of 2007 being beaten in 2011, and that new record smashed this year. Even taking into account the AD, the weather of the last two years hasn't been as conducive to ice melt as 2007. After 2011 I was wavering in my view that we'd have late summer sea ice through until late next decade. Earlier this year I said I'd reconsider after this year, and what happened this year?
From June when the ice retreat began in earnest inside the Arctic basin, the ice was retreating abnormally rapidly. This is seen in Cryosphere Today area anomalies (my calculation - 1980 to 1999 baseline).
The early August cyclone did have a significant effect, but even before that anomalies from the baseline were well below even 2007, without the cyclone it was still very likely that 2007's record would be broken. The early August cyclone merely exacerbated what was already likely by the end of June, a new record was going to be set.
Following the near elimination of the oldest ice I had anticipated that the volume loss would abate. This is a reasonable expectation given that the preceding interannual trend of volume loss had been from loss of old thick multi-year ice, as shown by ICESat and PIOMAS. Against the volume loss would then be the thinner younger ice with its fast response times, more able to rebound from forcing events like 2010 and this year. The rebound of younger ice has come into play, the first graphic in this post shows that happening in the PIOMAS domain. In the real world the larger area (CT) losses of years since 2007 have been countered by larger growth, enlarging the seasonal cycle. There are two processes happening here, discrete in time and process: During the melt season (Mar - Sept) thinner ice has more readily revealed open ocean, while during the early freeze season large new areas of open ocean have vented most of the energy gained during the summer into the atmosphere leading to delayed but ultimately vigorous horizontal spread of ice, with subsequent thickening over winter, a negative feedback on the summer's ice albedo feedback driven recession. But this is not enough as the volume losses have continued. I see no negative feedbacks that are likely to come into play that aren't already active - the overall feedback is strongly positive.
I'm now pretty well convinced that we are in a Rapid Ice Loss Event (RILE), probably a doozy of a RILE. I can see two main problems with this viewpoint, the biggest one is that March 2012 shows no evidence of a further loss of volume, but I'm expecting further March volume loss this year. The second is the role of weather.
It may seem that the involvement of weather in 2007, 2010, and the AD in the post 2007 era detracts from this view point of an ongoing RILE. However Holland notes in her presentation that RILEs are driven thermodynamically with ice dynamics playing a small stabilising role. In other words, in the models RILEs aren't driven by factors like ice-albedo but are driven by atmospheric and oceanic processes causing influxes of heat into the Arctic. In the extreme AD event of 2007, the assertion of the AD thereafter, and the unusual combination of weather leading to 2010's PIOMAS volume loss, we are seeing atmospheric processes that are thermodynamically driving ice loss. The processes behind the post 2007 assertion of the AD are not yet clear, snow forcing may play a role due to earlier snow melt. But it strikes me as stretching coincidence too far to claim there is no feedback and that the AD just happened to assert itself in the wake of 2007, when ice thickness had been substantially reduced, and ice retreat during the year had stepped into a faster gear.
The volume loss of 2010 was driven by the Warm Arctic Cold Continents pattern pre-conditioning ice in the winter and a massive warm anomaly over Northern Canada. In the case of the former, Cohen has shown linkage to the state of Arctic sea ice (more here), and in the case of both factors, they would not have had the dramatic impact but for decades of pre-conditioning, as the 1981 volume loss shows.
The Arctic atmosphere, and ocean are not passive players in the changes that are afoot, and their net role is to hasten ice loss.
If I take any one aspect of my argument I can see reason for doubt, reason to delay expressing this opinion, but when I put it all together I'm battered into submission by the overall pattern of the evidence. If I delay until I'm absolutely certain I might well be calling the blog post; "Well that was a RILE!"
So if I do think we're in a RILE, what do I expect to see in the future? I anticipate a rapid transition by 2020, but it may be much earlier. Given that I don't think anyone really has a grip on what's going on I don't think anyone can say for sure how fast it will be. Simplistic hand waving about ice-albedo effect driving the process neglects the AD role I outlined in my previous posts, and tells us nothing about the interplay between ice albedo and heat loss in autumn due to open water and thinner ice. As I accept that I have no more of a grasp of this than I think anyone else does, I'm not hazarding guesses as to how exactly the whole thing will play out. It's enough to say: By 2020 possibly much sooner. Which is vague enough to cover a lot of the uncertainty, but represents a substantial shift from where I was a year ago.
However in the course of the next 12 months I do think it's possible to outline the following bullet points shaping what I expect.
- I don't expect to see a substantially delayed refreeze of the same order as 2007, that's because there's not been the sunny skies over open water seen in 2007. Once it gets started the refreeze will be fast.
- I expect a volume loss between PIOMAS maxima for March 2012 and March 2013. i.e. this year's losses will not be made up over the winter.
- I expect large positive anomalies of NCEP/NCAR temperature in the lower troposphere, biassed towards the surface, from February to April. That's not to say it will be warm, but it won't be as cold as in years before 2010.
- Piomas volume anomalies will fall throughout May - June.
- I expect large positive anomalies of NCEP/NCAR temperature in the low to mid troposphere in May and June. Again, maintaining the apparent warming since 2010.
- There will be a massive crash in Cryosphere Today area anomalies during early June. Going at least as low as 2012, probably lower.
- There will be the development of a high pressure anomaly over Greenland in June persisting through July and into August. This will form an AD anomaly in tandem with low pressure over the Siberian sector.
- CT Area at minimum in September will be lower than the 2011 record of 2.9M km^2, likely at least matching this year's record, which is 2.23M km^2. There remains the significant possibility of a further crash well below this year, I can't hazard a guess as to the magnitude of such future crashes.