As I outlined in my post In Flux, a key finding concerning the Arctic has made me wonder about whether we are indeed on a fast-track to a seasonally sea-ice free Arctic this decade. However on reflection that is in part an emotional reaction to an observation that unsettles me. I had been going to wait until September to post on this subject, so I could see what happens this year: I still see 2011 as having the makings of a spectacular season. But in the light of Maslanik's latest paper, and of the points raised by two commenters on the 'In Flux'page, I thought it might be as well to state in detail why, on balance, I don't think we are on a fast-track, and why I think key observations are being misinterpreted.
Update - I have since changed my view on this as outlined in this post.
In the In Flux post I've explained my basic disagreement with the extrapolation of volume method and what it implies, so I won't go over that again here.
To start, it's as well to go over the paper by Tietsche et al which was raised by Kevin O'Neill on the In Flux comments.
What the authors do is use a climate model to examine the factors behind the recovery of sea ice in a climate model. They remove all the sea ice on 1 July at several points in the 21st century, the study finds that the factors are similar for each period, so the study concentrates on what happens after the sea ice is removed on 1 July 2020.
The graph deals in net fluxes, so taking the example of sunlight, the yellow line (known as shortwave radiation); immediately upon removal of the sea-ice there is an increase in shortwave. This is not due to an increase in incoming sunlight but due to the darker ocean being exposed. Because the ice is white it reflects back most of the shortwave that hits it, so it reduces net shortwave. However the ocean absorbs most of the shortwave that hits it, this means less shortwave is reflected back into space, so it increases net shortwave. Much of the ocean warming is due to the absence of ice, normally melting that acts as a heat-sink. This leads to an increase in net energy absorbed by the Arctic region (black line). Gradually as September is aproached the insolation falls, so that by September fluxes are near zero. But once the sun sets for the long Arctic night the ocean, which had warmed substantially during the summer loses much of it's heat.
Into the autumn the ocean emits sensible heat (heat you can feel or 'sense'), latent heat (heat due to evaporation and the phase transition from water to ice), and long-wave (or infra-red) radiation. By November sufficient heat has been lost by the ocean for it to cool to freezing and begin to freeze.
Despite the extreme nature of the experiment, removing all sea ice abruptly at a peak season in the summer. Tietsche et al find that after only two years the sea surface temperatures have returned to range of natural variability, and the sea-ice rebounds. For surface air temperatures they find a large increase in temperature between October and February that mainly affects the lower troposphere, this is similar to the observational findings of Serreze et al 2009 for recent changes in the Arctic.
Tietsche et al answer the question: What happens to the energy gained by the Arctic following a simulated loss of sea-ice? They find that the energy is mainly lost to the atmosphere in the following freeze period and thence radiated to space, or in warming the atmosphere reduces atmospheric heat fluxes into the Arctic.
Tietsche et al also note that:
"Between 2000 and 2040, when the rate of decline is
maximal, Arctic summer sea-ice extent exhibits strong year-
to-year fluctuations. As noted by Holland et al.  and
Notz , this increase in variability is mostly due to
changes in the ice thickness distribution and does not
necessarily indicate proximity to some critical threshold."
I think that what we have seen in reality is similar to the process Tietsche et al found in their model. 2007 and a massive loss of ice, in both area/extent and thickness implied by loss of MY ice. Then 2008, 2009, 2010, all offset to a lower extent by 2007 yet not showing similar losses i.e. Cryosphere Today Area. And the energy gains of those years causing - not further declines in area - but a delay to the re-freeze as shown by the low anomalies after the summer melt season i.e. Cryosphere Today Anomaly. It's tempting in view of this study to view the large late year negative anomalies as being the process identified playing out through 2007, to a lesser degree 2008 and to an even lesser degree 2009 and 2010. Although it should be accepted that we've had only one major drop (2007), and there were also anomalously high extents of open water through the following summers.
The continuing volume decline shown by PIOMAS does tell us that some of the energy gained in recent years is being used to melt ice, and this at present apears to be accelerating. However if I'm correct in what I outline, what we will see in the coming years will not be a collapse to a seasonally sea-ice free state, but a reduction in the rate of volume loss. That said, due to certain modelling studies I am expecting further losses like 2007, that will be lead by weather events. I'm in the process of writing about three key modelling studies at present.
It still bothers me that the accelerating volume loss is occurring as the MY ice is stabilising, but there is one personal quality the Arctic has taught me since 2007 - patience.
So on balance, as I see it, the main problem is that people seem to be confusing the effects of thinner ice cover with the suggested intial symptoms of a rapid transition to a seasonally sea-ice free state.
Maslanik's recent study, discussed in the preceding post, states:
"The recovery in multiyear ice extent through March 2011
from the extreme reductions in 2007 and 2008 along with
the continued aging of the surviving ice through multiple
melt seasons is consistent with an ice pack that has not
passed a tipping point across the Arctic Ocean as a whole..."
As I've said before, formerly the ice-pack had a large amount of multi-year (MY) ice at it's core. This core, stabilised the ice pack by virtue of it's bulk, mechanical strength, and the lack of brine inclusions in the ice. As the ice ages it loses it's brine inclusions which both strengthens it and increases it's resistance to melt, and it ridges forming ice much thicker than that which grows thermodynamically. That old ice-pack is now gone as I have shown in the earlier posts on MY sea ice.
So what has happened in the first decade of the twenty first century is that the ice has transitioned to a younger thinner ice pack which is less stable than the old pack was, (e.g. Maslanik et al, 2007). This process has been ongoing for decades before the final transitional period, but we have now gone through the transition itself, which did turn out to appear like a non-linear threshold (i.e. Nghiem 2007 - see here) From my perspective 2007 is an outcome of this process of transition, not a herald of a rapid transition to a seasonally sea-ice free state. What happened in 2007 was an episode of weather 'taking advantage' of the decades long process of loss of MY sea ice, and in the process removing more of the MY ice.
In terms of what is going on in the Arctic I think that the prognosis is the single most important aspect. It's crucial too in terms of the wider public debate about Climate Change, not the faux-debate about whether it's real and ongoing - there is no such debate, but in terms of how serious Climate Change is and how we should respond. It is also crucial that claims about the future should not put us in a position whereby the public gets tired of overstatement and flawed prognostication. It is only by discussing the process and it's mechanisms that we can better understand what is going to happen and what public statements to make about that.
If the idea that the Arctic will be sea-ice free by around 2016 becomes widespread, and I think it already has: Come 2016 when there is no sign of a crash to sea-ice free state, what are people going to say about it to a wary public, tired of overstatement and perceived alarmism?
I know what I'll say if it does happen - I was wrong, this is way worse than I thought it was.
Maslanik et al, 2007, "A younger, thinner Arctic ice cover: Increased potential for rapid, extensive sea-ice loss."
Maslanik et al, 2011, "Distribution and trends in Arctic sea ice age through spring 2011."
Serreze et al, 2009, "The emergence of surface-based Arctic amplification."
Tietsche et al, 2011, "Recovery mechanisms of Arctic summer sea ice."