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Posts Tagged PIOMAS

Gone for good: Arctic Ocean ice free all year by the 2040s? Gareth Renowden Oct 18

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A few days ago I used a combination of Arctic sea ice volume data from the University of Washington’s PIOMAS model and NSIDC sea ice extent numbers to project that the Arctic Ocean would be effectively ice-free in late summer within ten years. The key to that exercise was the rate at which the volume of sea ice has been declining — 350 km3 per year over the last 30 years for the full dataset, 410 km3 per year over the last 20, and 740 km3 over the last decade at summer minimum. The rate of volume decline has obviously been increasing. Using those numbers to project ice extent in the future is one thing, but they also tell us something interesting about the overall Arctic heat budget — and we can use that to make a rough guess about when the Arctic will become ice-free year round. The answer is surprising…

The Arctic heat budget is the balance between the heat being shipped to the top of the planet by the summer sun, the atmosphere and ocean currents, and the heat lost over a sunless winter. The sea ice volume trends tell us that the polar heat budget over the last three decades has been dominated by excess incoming heat — enough to melt hundreds of cubic kilometres of ice every year. We don’t need to worry about the details at this point — we don’t need to look at all the items in the budget, positive and negative, but like a good CEO we can focus on the bottom line, and that’s what the volume decline represents.

Another aspect of the volume data tells us something else about the budget: the amount of heat lost over winter. If we take the full 30 year PIOMAS data, the average maximum ice volume is 28,600 km3, and the average minimum is 13,400 km3. In other words, in what used to be an average winter the Arctic lost enough heat to grow 15,200 km3 of new ice. Let’s be generous, and assume that in current circumstances (starting from a low summer minimum) winter ice growth is potentially around 20,000 km3.

Once the perennial ice has gone, the Arctic heat budget will not simply stop showing a surplus. Instead of melting ice, energy will go into heating the ocean and atmosphere. More heat will have to be lost each autumn before ice can start to reform, and the arrival of the first ice of winter will be delayed. This effect can already be seen in the data. Take a look at the area anomalies at Cryosphere Today — they are already greatest after the late summer minimum, reflecting the delayed formation of new ice (more on that here). The greater the delay, the smaller the volume of ice that will regrow over what’s left of winter. At some point in the future enough heat will have accumulated in the ocean to prevent winter ice formation, and the Arctic will have completed its transition to an ice-free state.

…it may be already too late to do anything to prevent the Arctic sea ice disappearing completely

How soon could that happen? The ice volume data provides a simple way to arrive at an estimate: divide the normal winter heat loss by the annual heat surplus. At 350 km3 of ice lost per year (the 30 year volume trend), it will take 57 years. If the Arctic is seasonally ice-free by 2020, then it will be ice-free year round by 2080. However the recent volume loss has been running at 740 km3 per year, and if that rate continues it might only take 27 years for the winter ice to disappear. If the summer ice is gone by 2016, as might be possible at that rate of decline, then the Arctic could be ice-free in winter as early as 2043. This is not only much faster than most researchers have been willing to countenance, but also falls within the 30 year climate commitment — the inevitable warming caused by current greenhouse gas levels, as the climate system comes back into thermal equilibrium. If my sums are right (please, prove me wrong!) then it may be already too late to do anything to prevent the Arctic sea ice disappearing completely.

This speculation is clearly a considerable over-simplification — not a back-of-the-envelope calculation so much as a topologically infeasible back-of-the-back-of-an-envelope scribble — but the basic logic seems sound to me. The mechanisms that are creating the Arctic’s energy surplus may not operate the same way in future — negative feedbacks may come into play (increased cloudiness, freshening of the surface layers of the ocean), but so will positive feedbacks such as the “albedo flip” (replacing ice with dark ocean will increase heat absorption from solar radiation). The balance between those factors will determine how long it will actually take to move to a permanently open ocean, but there are signs we are heading that way at some speed.

We have a good analogue in the geological record for what a warm Arctic might be like — the Paleocene Eocene Thermal Maximum 58.5 million years ago. A sudden warming episode, probably associated with the release of a large amount of methane from oceanic methane hydrate deposits, saw Arctic sea surface temperatures spike up to 24ºC, and there’s evidence of sub-tropical vegetation (specifically palms) growing on neighbouring land masses. Not good news for the Greenland ice sheet, or the huge amounts of methane hydrates trapped under an already melting permafrost cap on the seabed off Siberia…

When I wrote Hot Topic (over NZ summer 2006/7), I suggested that the Arctic might be ice free in summer during my lifetime and thought I was going out on a limb by saying that. The record retreat of the sea ice in 2007 was a worrying confirmation of my gut feeling. Now it seems possible that if I can hang on until I’m 89, I might see the Arctic lose all its sea ice. The complete and utter transformation of a planet in my lifetime. And still we do too little, too late…

[The Shins]

Five years (threnody for Arctic sea ice) Gareth Renowden Oct 16

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Earlier this month the US National Snow & Ice Data Center issued its analysis of this year’s Arctic sea ice minimum — at 4.60 million km2 on September 19, the third lowest extent in the satellite record. However extent (defined here) doesn’t tell you everything about the state of the ice — according to the University of Washington’s PIOMAS ice model 2010 managed to set a new record low for sea ice volume.

In terms of the future of the Arctic sea ice, the volume of ice remaining at minimum is a crucial metric because it represents the size of the heat budget buffer between an ocean with a perennial floating ice cap and one that’s seasonally ice-free. For the Arctic to be ice free in summer, that buffer has to disappear, or become a lot smaller. I’ve been writing about sea ice volume for some time, and considered the overall Arctic heat budget in this post a couple of years ago, so news of the new low volume prompted me to think about what it might mean for the extent metric over the next few years. To do that, I downloaded the NSIDC’s September monthly average extent for the last 21 years, and plotted that against the PIOMAS model’s September average monthly volume (kindly supplied by Jinlun Zhang). Here’s what the data looks like when you plot it on the same chart.

SeaIceData.png

The red line at the bottom, labelled “thickness”, is what you get when you divide volume by extent, and that too has been in decline, reflecting the fact that the loss of volume has been happening faster than the reductions in extent.

“Thickness” is not a real representation of the actual thickness of the ice at minimum — that varies considerably with the age of the ice, older ice being thicker. It’s just a number that depends on the relationship between extent and volume, and that makes it interesting. Here’s what it looks like if you plot it at a finer scale:

thickness.png

In 1990, the sea ice at minimum was 2.2 metres “thick”. In 2010 that had declined to 0.94 metres — reflecting the marked loss in old thick ice over the period. Over the 21 year period, the ice has been thinning at about 4 cm per year, and over the last decade — reflecting the steep recent drop — at 8 cm per year.

For sea ice volume, the PIOMAS numbers show an average drop of 410 km3 per year since 1990, but over the last ten years that loss increases to 740 km3 per year, mainly because of the steep falls in 2007 and 2010. For extent the 21 year trend is a loss of 110,000 km2 per annum, rising to 200,000 km2 per year over the last decade.

So what happens when we project these trends forward? To do this I plotted two graphs, the first assuming that the 21 year trends for volume and “thickness” would continue over the next ten years. From those numbers I calculated the equivalent extent:

21yrtrend.png

By 2020 September average sea ice extent is reduced to 850,000 km2. The following year (not plotted) it reaches a minimum of 90,000 km2. In other words, if the rate of reduction of ice volume continues at the average rate of the last 21 years, the Arctic will be ice free in summer by 2021.

What happens if you plot the same graph, using the current (last decade) trends for volume and “thickness” to project extent? It’s a striking picture, I think you’ll agree:

10yrtrend.png

If these trends continue, then September ice extent dips below 2 million km2 in 2015, before all but disappearing in 2016. Hence the title of this post…

I also looked at what happens if you use the trends in extent and “thickness” to project volume going forward. This results in ice volume reduction at half the rate observed over the last two decades (a quarter of the current rate), and so looks unlikely — although it does postpone an ice-free Arctic summer until 2030/31.

Of course, these projections are very “smooth”, and make no allowance for the year to year variations that are obvious in the records for volume and extent. That “noise” could work to our advantage, and delay the loss of ice. For instance, if volume reductions occur at the rate apparent in 2002-6, then 2020-21 looks possible. On the other hand, just one more year with a drop in volume as large as in 2007 or 2010 could bring the end of the ice before 2015.

Some caveats: the PIOMAS data is model generated, and while regarded by the sea ice community as the best available at the moment, it is subject to uncertainty. The absolute numbers could be wrong, as could the exact trends, but the big picture is all I’m really relying on for these projections. Improved volume numbers should become available as the new Cryosat 2 mission begins to produce data.

Bottom line: if the relationship between ice volume and extent evident in the NSIDC and PIOMAS data over the last 21 years continues in the near future, then the Arctic will be effectively ice-free in late summer sometime between 2015 and 2020. One interesting observation: the 10 year trend chart above suggests that 2007′s record minimum extent could remain unbroken next year, and the ice would still be on course to disappear within five years. If there’s any upside at all to this message (and I’m struggling to find one) it is perhaps that such a rapid and visible loss of sea ice might finally persuade the international community to take urgent action to reduce the atmospheric carbon load. What a seasonally ice-free Arctic might mean for global climate is something I shall look into a future post.

My thanks to Jinlun Zhang at the University of Washington for supplying the PIOMAS data. My amateur prognostications should not be taken as endorsed by him or the PIOMAS team, the NSIDC or any respectable sea ice scientist for that matter. ;-)

[Bowie, 1972]

Arctic sea ice projections: 6 billion dead within a year (it really is grim up North) Gareth Renowden Jun 25

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The first set of ARCUS/SEARCH projections for the September Arctic sea ice minimum have been released, and amid all the mundane statistical, heuristical, and modelistical musing there’s a remarkable effort — and I really do mean remarkable — by one Charles Wilson. Here’s the graphic showing all of the submitted forecasts. See if you can spot Mr Wilson’s offering:

ARCUS1006.jpg

Yes, that’s him on the left. He appears to have no affiliation to any academic institution, but he is not afraid to make a very definite projection. Download the full set of forecasts [pdf], and take a look. He expects a massive melt, leaving the Arctic Ocean more or less ice-free by September. That’s pretty scary, but here’s what he thinks this may bring for the northern hemisphere. Ocean current disruptions will bring 300mph winds to the northern hemisphere:

= Destruction of nearly ALL aboveground structures North of 10 Degrees Latitude = 99% Deaths in USA, Europe, etc. within 2 years. … In the Worst Case:
Immediate Action can create Clouds with: Airplane contrails, seawater mists, or high- altitude sulfur (e.g. heightening Smokestacks at Norilsk).
But it needs to be done in the next few Weeks – – – months before we can be sure an Early Melt WILL happen.

In a comment at µWatts he expands his point a little:

If the Great Melt Off happens = Warm Currents turn around = 300 mph Winds come February or so..
Currently I give it 15%
… times 6 Billion dead.

Now that’s what I call alarmist.

There’s further coverage of the projections at Skeptical Science, and Neven’s excellent new Arctic Sea Ice blog, but to me the Proper Scientists look to have been pretty conservative. The June report is based on May numbers, so the rapid melting of recent weeks hasn’t yet been accounted for. It’ll be interesting to see how things change in the next report, due in July (I think). Put me down somewhere between Maslanik and Gauthier et al…

For a one-stop review of all the latest numbers/graphs and pictures, the aforementioned Neven has assembled a great selection here. Worth a daily visit for the next six to eight weeks, at least… Today’s notable change: the PIOMAS team have updated their ice volume graph, and it continues to drop further below trend. Perhaps Mr Wislon, who sets great store by the PIOMAS numbers, is on to something. But I hope not.

My white ice cycle Gareth Renowden Jun 03

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Eli Rabett, that ever-curious but lovable lagomorph, has noticed the appearance of an apparent annual cycle in the Arctic sea ice area anomaly chart at the excellent Cryosphere Today. I mentioned the same thing in a post on Arctic sea ice back in April, and hinted that I might look at it “another day”. Well, that day has come, not least because the ice “experts” at µWatts have been suggesting it might be a satellite problem (it isn’t).

Here’s the relevant chart from Cryosphere Today. I downloaded it last night, and added the crude red circle round the interesting bit (click the image to see the current version of CT’s graph — it updates daily).

100602seaice.anomaly.arcticedit.png

It covers the entire satellite record, and shows the anomaly — that is, the difference between the actual ice area for a given day and the average ice area for that day over the entire period. Looking at the anomaly should remove the annual cycle, because that’s accounted for in the average that forms the baseline. Nevertheless, from 2007 onwards it looks very much like the anomaly is itself showing an annual cycle.

100602seaice.anomaly.arcticcrop.png

Here’s a close up. The first big drop occurs in 2007, the year of the record summer minimum area, but it’s there again in 2008 and 2009 — and shows every sign of happening again this year. If you look closely, you’ll see something just as interesting as the cycle itself. The maximum anomaly occurs after the summer sea ice minimum. This is obvious on CT’s graph of area over last two years. The red line at the bottom is the anomaly, and you can see that the maximum anomaly occurs after the ice area has started to regrow — which means that the freeze-up has begun later than the 30-year average. However, once the ice starts refreezing, the anomaly decreases rapidly and gets up towards the zero line over winter. So what’s going on? Why is the late summer anomaly so much greater than the winter anomaly, and why have we only started seeing the cycle in the last few years? Here’s my stab at an explanation…

Consider the geography of the Arctic sea ice. You can divide it very roughly into two regions — the ice in the Arctic basin, that is the ocean around the pole, north of Canada, Alaska, Siberia, Svalbard and Greenland, and the sea ice that forms outside the Arctic basin (Barents Sea, Bering Strait, Kamchatka, etc). Every winter the Arctic basin freezes up. That happens every year without fail (so far). The winter anomaly therefore depends on the amount of sea ice that grows outside the central Arctic. But all that ice melts long before we get anywhere near the late-summer ice minimum — in other words, it’s irrelevant to prospects for the summer.

Summer anomalies are determined by the ice melt in the central Arctic. Up to 2007, the summer melt mainly took place around the Canadian and Siberian shores, and in the Barents Sea. That’s why the Northwest and Northeast Passages were/are a tricky proposition — they depend on the fringes of the polar sea ice cap melting. In 2007, however, ice over a large chunk of the central Arctic basin melted away, setting a new record minimum by a 25% margin. That delayed the start of the freeze-up significantly, and so the anomaly increased to more than 2.5m km2 below average. But this is the central Arctic we’re talking about, and still a very chilly place, so even though the freeze-up was delayed, the sea ice regrew as autumn turned into winter and covered the entire basin.

The emergence of an annual cycle in the anomaly therefore occurs because there’s now more variability in summer area/extent than there is winter area/extent, and because there is, in absolute terms, more central Arctic ice to lose. 2007′s record melt triggered the appearance of the cycle. And as and when we hit new record minima, we’re likely to see even bigger swings in the cycle as long as the entire central Arctic freezes up every winter.

[This is not news to real ice scientists, by the way, because model runs show similar sea ice behaviour as the ice declines -- though it's being seen rather sooner than modelling suggested. This post at Primaklima at Scienceblogs.de shows some examples. H/t to Georg himself in comments at µWatts]

There is another tantalising hint to be discerned in the new cycle. In each of the last three winters, the anomaly has approached zero — and sceptics have been keen to trumpet the ice as being back to normal. As we’ve seen, this is because of the growth of sea ice outside the Arctic basin, and so it is irrelevant to the state of the ice that will melt the following summer. The slightly reduced winter anomalies (compared to the four or five years prior to 2007, though not earlier) might be related to changes in weather patterns outside the central Arctic (which has been warmer than average throughout recent winters, while parts of Siberia have been colder), or perhaps to reductions in salinity caused by greater run-off of fresh water (making it easier to freeze) — but that’s highly speculative.

IceVolumeAnomaly100530.png

It’s interesting to note that the annual area anomaly cycle is to a certain extent mirrored in the PIOMAS ice volume data. Here’s the last few years snipped from their latest chart. There was a record volume anomaly in summer 2007, as you might expect, followed by a recovery over winter as the ice cover regrew. Another minimum occurred in summer 2008, followed by a smaller regrowth, and then another drop to a record minimum in summer 2009. Not much new ice since, though, and in the last couple of months the volume anomaly has plummeted. They’ve had to add another section to the bottom of the chart since I last posted it here…

Talk of betting on the summer minimum is underway at the mustelid’s place, and I am on record there as suggesting that this summer will see a greater melt than the last couple of years. A new record? Perhaps, but I’m not betting on it. Meanwhile, the SEARCH forecasting exercise has posted its first “pre-release” ice forecast: Adrienne Tivy, a post-doctoral fellow at the International Arctic Research Center (IARC) has developed a statistical model that projects a 4.539m km2 Sept average, “below normal” but way above the last three years. Still, when you look down on the top of the world (or bottom, from my perspective) from the vantage of NASA’s Terra and Aqua satellites, the eyeballs in the sky (there is life beyond the pooliverse!) make the sea ice look very broken up and mobile. Click on the little image at the top of the post (which shows open water at the western entrances to the NW Passage yesterday) to see the latest Arctic mosaic, and make up your own mind…

[Tomorrow -- another dreadful pun, sorry. ;-) ]

Feel floes (gone by 2016) Gareth Renowden Apr 27

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The usual suspects have been making much of the fact that over the last few weeks Arctic sea ice extent (NSIDC daily graph here) has been bumping around the 30 year average for this time of year. John Cook at Skeptical Science posted on the subject last weekend, making the important point that what matters most is not extent or area, but the total volume of ice that’s present — and that’s showing no signs of “recovery”. John’s post is well worth reading, but it set me off on a very interesting trawl through the references he provided — and drew my attention to a most useful graph of ice volume and trend. It also pointed me to research that suggests the Arctic could be effectively ice-free in summer within ten years — possibly as soon as 2013.

Here’s the graph that caught my eye. It’s produced by the Polar Science Center at the the University of Washington in the USA, and is regularly updated — this was generated on April 17th.

Icevolanom100417small.png

It shows the sea ice volume anomaly and its trend, as calculated by the Pan-Arctic Ice Ocean Modelling and Assimilation System (PIOMAS) developed Dr J Zhang and his colleagues at the PSC. It’s important to note that this is the anomaly that’s being shown — the difference between the ice volume on a given day and the average for that day over the full 79-09 satellite record (in other words, the seasonal cycle is removed). The blue line is the trend (- 3,300 km3 per decade) and the grey bars show one and two standard deviations from that trend. Two things are I think obvious: the ice volume has been steadily declining over the last 30 years, and the rate of loss looks to have increased markedly over the last ten years. We’ll come back to that point…

Now lets compare that graph to the sea ice area anomaly as calculated by the Polar Research Group at the University of Illinois, from their Cryosphere Today site.

iceareaanom100425small.png

I grabbed that graph a day or so ago, from here. It updates daily, so the end point will have changed, but the history won’t. Again, we’re looking at the difference from average for any given day in the record, with the seasonal cycle removed. There’s been a steady decline over the last 30 years, and a noticeable steepening over the last ten. So what’s the difference between area and volume? The thickness of the ice, of course. Estimates of extent or area give us only 2D information — but the amount of ice floating on the Arctic Ocean is the area times the thickness.

Now focus on the most recent three years on both graphs. You’ll recall that Arctic sea ice recorded a new record low summer minimum in 2007. Looking at the area anomaly, you can see that clearly as the lowest spike on the graph — the minimum was over 2.5 million km2 below average. The anomaly then gets smaller as the winter freeze-up continues, bigger again in summer, and so on. What’s striking is that the amplitude of the “cycle” between low and high anomalies has become much larger since that 2007 record melt. Why that might happen is an interesting question (for another day, perhaps).

The PIOMAS data provide a different perspective. The 2007 summer low is obvious on the graph, but it is no longer the lowest point. That was reached in 2009. In Feb-Mar 2009 the Arctic sea ice volume was 11,900 km3 — below the average minimum September volume over 79-09, and the current volume is only slightly above that. In other words, the sea ice hasn’t “recovered” by any stretch of the imagination — it’s two standard deviations below the trend, which is already showing decline of 3,300 km3 per decade. The PIOMAS numbers reflect the loss of thicker multi-year ice in recent years, replaced by thinner one and two year old ice.

What happens if you look at the recent sea ice volume trend and project it into the future? Here’s a graph from a presentation [pdf] by the US Naval Postgraduate School’s Prof Wieslaw Maslowski, given at the ARCUS State of the Arctic conference in Miami last month (anyone interested in Arctic research will find a treasure trove of material at the conference web site):

IcevolprojectionMaslowski.png

This shows the October-November ice volume over the last 30 years and five different estimates of the current rate of decline in those months. The most recent data (from Ron Kwok’s team at NASA) is consistent with a rate of decline of about 1,000 km3 per year. The green line on the graph shows the volume of ice left in the Arctic when there’s a bit clinging to the Canadian archipelago and Greenland (see the little map above). Maslowski therefore projects an “ice-free fall by 2016 (±3yrs uncertainty)”. Not having been present at his talk, I can’t tell you exactly how he put that in words, but the graph and quote come from his slides. Maslowski is well known for his aggressive projections for summer sea ice loss, but this is the first time I’ve seen his argument quantified.

I’m still mulling over the implications (not least for sea ice bets). On one level, it’s confirmation of a worrying projection — an ice-free Arctic Ocean in late summer within the next ten years. The consequences of that, for both the climate of the northern hemisphere and the geopolitics of the Arctic are huge. On the other hand, there are undoubtedly arguments as to why this might not happen — at least, not so soon. A run of cool summers could allow the ice volume to rebuild as it did in the early 1980s. First year ice could become second year ice, then third year and so on. That seems to be within the range of natural variation in the PIOMAS numbers, but it might only postpone the inevitable by what — five or ten years?

Here’s the context: the IPCC’s fourth report put Arctic summer sea ice loss out into the second half of the century. Current volume numbers are consistent with loss within ten years. Warmer Arctic autumns mean snowier northern hemisphere winters and significant changes in weather patterns. The sea ice is not recovering — instead it shows that rapid climate change is happening here and now. And that’s not alarmist, it’s truly alarming.

[Beach Boys: apologies for the appalling pun, but I'm running out of relevant song titles for ice posts. All suggestions gratefully received.]