Unfortunately I couldn't include PIOMAS in the last blog post I did on sea ice thickness models, but to make up I'm putting up the latest volume data from the PIOMAS model, as calculated by FrankD.The graph was updated a few days back and the anomaly trend line seems to have dipped below 2 STD again.
As was discussed in the comments following Larry Hamilton's excellent Trends in Arctic Sea Ice Volume, these numbers differ slightly from the official PIOMAS numbers, because the latter are obtained by running several ensembles, whereas the PIOMAS graph (on which FrankD bases his dataset) on the website of the University of Washington's Polar Science Center is based on the results from the ensemble that has the best overall performance.
FrankD has also sent me this graph with simple quadratic trend lines for each month (click for a larger version):
Oh great, just in time for Apophis...
Posted by: Artful Dodger | May 11, 2011 at 18:57
In case you haven't noticed yet, the PIOMAS linear trend is now down to -3,600 km^2 per decade (as per the UWash/APL Chart above).
Posted by: Artful Dodger | May 11, 2011 at 19:42
Does anybody know why the Ice Volume Anomaly took such a extreme spike last June/July?
Very strange how it dropped so low and then recovered just about as quickly and to near the same anomaly level it was before.
Behavior over the last 5 months or so seems more reliable and believable. I'd tempted to dismiss some of last years data as a fluke.
Posted by: Andrew Xnn | May 11, 2011 at 23:22
Andrew,
It's important to remember that PIOMAS is a model and so it does not produce any actual "data"- it is not measuring anything real, but only spitting out what the model says the thickness of the sea ice MIGHT be. You can believe that the thickness of the sea ice did not actually spike, for it would be a physical impossibility to do so. Rather, the input variables that the PIOMAS model uses changed rapidly over a period and gave the spike. I'm fact, such spikes in models are good indications of potential weaknesses in the models ability to filter out short term fluctuations or inherent noise in what should be a smooth curve in the actual physical thickness of the ice over time.
Posted by: R. Gates | May 12, 2011 at 01:44
R. Gates,
I wouldn't say PIOMAS is just a model - it is the Pan-Arctic Ice Ocean Modeling and Assimilation System. The "assimilation" part is important, and keeps the model grounded in many different types of measurements, not just a long computer model run from initial conditions in 1979.
Assuming PIOMAS is fairly accurate, as previous comparisons to IceSat data showed:
http://psc.apl.washington.edu/wordpress/wp-content/uploads/schweiger/ice_volume/IceVolAnomaly19792010.MarNov2.png
you can see that 2010 had the lowest extent of the satellite era for that month:
http://www.ijis.iarc.uaf.edu/seaice/extent/AMSRE_Sea_Ice_Extent_L.png
June/July was lower than any other year, even 2007, which had an impressive spike down in anomaly.
(I'm assuming no years before 2002 were lower, based on this:
http://iup.physik.uni-bremen.de:8084/amsr/ice_ext_n.png )
Notice the extent for June was about 9 million km^2. If this ice was on average 1 meter thinner than usual for June, that would be an anomaly of 9000 km^3. To explain the 2010 anomaly spike of 3000 km^3, we would need that 9 million km^2 of ice extent to be 33cm thinner than usual (well, ice area, but this is just back of the envelope calculations...). Since there is also about 0.5 million km^2 of sea ice missing in 2010 compared to 2007, at about 2 meters thickness in June, that's 1000 km^3 right there, leaving the rest of the 9 million km^2 to be only 22cm thinner than usual in 2010, for that month.
Maybe it was less cloudy than usual that month, or the winds were a bit warmer, or the bottom melt was larger than usual, so the model, and measurements, showed the ice a bit thinner than usual.
The 3000 km^3 anomaly spike over a couple months is certainly NOT a physical impossibility. Later that summer, other years caught up to the extent and thickness of 2010 (maybe more clouds were forming, colder winds from Siberia, who knows...), so the anomaly went back to "merely" 1500 km^3 less than the linear trend.
Anomaly spikes just show that the timing of the summer melt, both thickness and extent, can be very different for different years. Of course, the anomaly is trending down, down, down...
Posted by: Anu | May 12, 2011 at 05:50
R.Gates is quite correct, it is as Patsy points out to King Arthur, only a model. But in the main, I'd agree with Anu - the anomaly is a reflection of the melt occurring 2 to 4 weeks earlier than average (of course, that also lead to a record low final volume).
This pattern is reflected in pure data as well, such as Cryosphere today's Sea Ice Area graph for Hudson Bay. The anomaly does not grow and shrink, exactly, but rather reflects the fact that the Bay is melted out earlier and froze over later than average (again, by several weeks).
Posted by: FrankD | May 12, 2011 at 07:30
R.Gates, thanks for checking in.
RE: "You can believe that the thickness of the sea ice did not actually spike, for it would be a physical impossibility to do so."
Please note that this 'spike' lasted through the melt season, and into the freeze season.
So in my opinion, it was not some short-term anomaly that can be dismissed as a 'fluke', but an indication of accellerated melt (and subsequent freeze) over a good part of 2010, which can certainly be real.
If the same 'spike' (accellerated melting) is going to occur again this melting season, would you be more convinced of it relation to reality, or not ?
Posted by: Rob Dekker | May 12, 2011 at 09:47
Spike or fluke, IMO it's as simple as Rob Dekker suggests. If it works out that way this summer, I should lower my estimated 3,8 MK with 1 MK. But sometimes I'm attracted to remain conservative, so I assume there will be some cloud protection during a part of the melt season.
For now, just look at MODIS. Draw a line between Cape Morris Jessup and Severnaya Zemlya. South of that line, I suspect that part of the pack is ready to be cleared when the ocean heat content in the North Atlantic pulses in during June/July.
Posted by: Werther | May 12, 2011 at 14:29
Yes, Hudson Bay melted out more than 30 days early.
Posted by: Artful Dodger | May 13, 2011 at 00:14
Hi Frank. Well mate, your Chart is famous. Would have been nice for Lou Grinzo to give you a shout-out, though... Cheers!
Posted by: Artful Dodger | May 13, 2011 at 00:50
Cheers Lodger, I thought it was a bit of a mess with all months plotted together, but some people found it striking, so...yay! "Information longs to be free", and all that. It's out of the bottle now and no shout-outs needed [but appreciated ;^)]
The thing I find funny is that I first fitted quadratics because I thought that the original linear trend fitted by the PSC guys to the anomaly graph was a bit "optimistic". Now that people (such as Lou's readers) are looking at the quadratic, they are observing that for the last four years all the data points are below the fitted curve, meaning that that acceleration is accelerating. It's about then that the "Oh, sh&t!" moment hits...
Posted by: FrankD | May 13, 2011 at 14:40
FWIW, the faster-than-quadratic decline in PIOMAS Sep volume was another reason I favored Gompertz curves as a naive model. Last 4 years are split above/below that curve, Figure 6 here:
http://neven1.typepad.com/blog/2011/04/trends-in-arctic-sea-ice-volume.html
Posted by: L. Hamilton | May 13, 2011 at 15:14
While I admire FrankD's graphing skills, I am unconvinced that the graph is not flawed as a predictor of an ice free Arctic.
I suspect that the graphs are a better indicator of when the Arctic will become free of thicker multi-year ice than an indicator of when the Arctic will be ice free.
Multi-year ice is steadily being replaced by first year ice. While it is difficult to obtain data on the rate of decline in thickness of first year ice, observations of the 4.25 million km2 region called the Arctic Basin on the Cryosphere today website suggest that this region is able to sustain itself. This region fairly quickly went from 2.5 million km2 at the September minimum to its maximum extent of 4.25 million km2 by late November of 2010 and has remained close this level through today.
http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/recent365.anom.region.1.html
The region appears to have slightly more ice area than it did at the same time last year. This region makes up a significant percentage of the ice remaining at the September minimum. I renew my comments from previous posts that the line drawing predictions need to be done using data only for the Arctic Basin region (area, extent, or volume) if they are going to provide an accurate prediction of when the Arctic will be ice free for a given month.
Posted by: William Crump | May 16, 2011 at 22:37
William,
I have on occasion reflected that there is some merit in focussing on extent as opposed to volume. Actual decline in ice derives from a mix of factors, in some of which extent is paramount (eg albedo effect) and in others volume is (disspation of excess heat in the process of melting ice). I am doubtful of the merits of your insistence that the Arctic Basin needs to be considered in isolation.
However, for me at least, whatever merits your arguments may have are lost in being distracted by your continued misprepresention of what I have shown in this graph.
Could I beg you not to continue to do so? I have repeatedly explained its context at length here, at ChatterBox, at Tamino's etc, and I will not bore the readers with further disclaimers about what it is and above all what it is not.
I have never claimed that it is "a predictor of an ice free Arctic", and I would be grateful if you would desist from suggesting that I have. If you choose to view it as a "predictor" that is your business. So far from claiming that it is, I have repeatedly affirmed that it is not.
I have only EVER claimed that quadratic curves fit the PAST data better than the linear fit shown on the graph on the PSC website, but have as often reminded that while a better fit, a quadratic is unlikely to be an accurate model of what is happening.
Can I make that any clearer?
My alleged graphing skills are also misrepresented - any idiot can use Excel, and quite a few do... ;^P
Posted by: FrankD | May 17, 2011 at 08:16
My alleged graphing skills are also misrepresented - any idiot can use Excel, and quite a few do... ;^P
Confirmed!
Posted by: Neven | May 17, 2011 at 12:24
- any idiot can use Excel, and...
Denied!
I can't and I am a 100% foolproof idiot.
Posted by: idunno | May 17, 2011 at 17:29
FrankD:
Is this just an excel line drawing exercise with no real world meaning?
If you do not believe that extending the lines of the chart beyond 2011 is a valid exercise,then why draw them until they reach a zero level?
What other interpretation of the graph is there?
There should at least be a disclaimer that the originator of the graph does not believe the lines on the graph represent an accurate forecast of future ice levels.
Posted by: William Crump | May 17, 2011 at 20:45
William,
I don't think there is anyone who would dispute that the Arctic Basin is crucial when one wants to "provide an accurate prediction of when the Arctic will be ice free for a given month".
FrankD's graphs show ice volume trend of the Arctic, and your opinion that these graphs are "a better indicator of when the Arctic will become free of thicker multi-year ice than an indicator of when the Arctic will be ice free." does not affect the notion that extrapolation suggests that 4 years from now the majority of ice volume consists of 'zero-year' 'ice'.
So my question to you is : What other interpretation of FrankD's graphs is there ?
There should at least be an explanation of why William Crump believes that graphs that stop in 2010 represent an accurate 'forecast' rather than an observation of an accellerating trend of ice volume reduction.
So what exactly is your point ?
Posted by: Rob Dekker | May 18, 2011 at 11:18
It seems to me that quibbling over whether or not the chart is an accurate predictor of ice free conditions is missing the forest for the trees. When I look at the chart I'm not focusing on the year the curves hit zero. I don't care. I'm looking at the big picture that says, "Hey folks, this boat is going over the freaking falls!"
I don't see much point in breaking out the stopwatches to estimate the exact second the boat gets dashed on the rocks.
Posted by: Robhon | May 20, 2011 at 19:35
Since we are going to be focusing on extent a little later this year I decided to brush off Tamino's calculations of last.
You can see what he used here:
Summer Ice
Tamino, 2010-07-26
http://tamino.wordpress.com/2010/07/26/summer-ice/
... and how well it served him here:
I got lucky
Tamino, 2010-09-22
http://tamino.wordpress.com/2010/09/22/i-got-lucky/
He predicted 4.78 million square kilometers and what we got was 4.81 million.
I duplicated his results just to make sure that I understood his calculations then included the data from last year. A quadratic fit of NSIDC September monthly gives 4.63 million square kilometers for this year.
That gives us a 0 September monthly around 2030, not 2016, 20 years rather than 5. And you can't have zero volume and still have a non-zero extent.
However, volume is 3D and the ice is being eaten away from above and especially from below. Something not taken into account by a quadratic fit of extent. So I would expect the quadratic fit of extent to become progressively worse over time.
Given my earlier (embarrassing) experience with quadratic fits, I still expect that a one time unit extrapolation will be fairly close, however. So I am projecting 4.63 for this year. Thoughts?
Posted by: Timothy Chase | May 21, 2011 at 19:18
Rob, I was thinking about what you have said and there is a great deal of sense to it. But as humans we are naturally curious about exactly how events will turn out even when what ultimately happens is largely a forgone conclusion.
Furthermore this sort of discussion somewhat playfully puts the spotlight on a very serious issue. It is an issue that people should be paying a great deal more attention to.
So oddly enough I view this sort of discussion as an important one -- because it gets people to thinking and discussing important changes that are taking place in our world. And we have to do at least that much if we are to begin to change the path that we are taking.
Posted by: Timothy Chase | May 21, 2011 at 19:29
So oddly enough I view this sort of discussion as an important one -- because it gets people to thinking and discussing important changes that are taking place in our world. And we have to do at least that much if we are to begin to change the path that we are taking.
That's what this blog is here for, Timothy:
"Furthermore, despite the ever-increasing evidence that the Earth's atmosphere is warming, that it is mainly caused by human emissions of greenhouse gases and that this potentially could have serious consequences for the world's ecosystems, economies and societies at large, there is still a large amount of controversy, mainly conjured up by contrarians, that undermines the public's perception of the problem of Global Warming and thus delays meaningful and positive action that is needed to mitigate and adapt to the consequences of an atmosphere and oceans being charged with a large amount of extra energy. The - up till now - spectacular story of the Arctic sea ice melt might change this and move the debate forward towards solutions. There's plenty to debate on that subject as it is."
Welcome to this blog!
Posted by: Neven | May 21, 2011 at 19:44
OK, here is my post in PIOMAS, like I promised.
Thanks for the comments from Gas Glo and others, which made me realize that, among other things, I had used the wrong terminology. So, in an attempt to sweep them all up in one answer, here's my attempt at a thought experiment.
Imagine that at Year 0 on September 15 at the minimum, you have 8 km3 volume of Arctic ice in an area of 4 km2, or an average thickness of 2 meters, with a standard deviation of 1/3 meter. Your average thickness is decreasing compared to past years at that time by 1 meter per year.
In Year 1 (or, if you prefer, 2010) you see a little more than 4 km3 of volume, a little less than 4 km3 of area, and average thickness of 1 meter. You see, about 2% of the ice (3 SDs out on the normal curve) has gone; it has "negative thickness". What happens to the water where the ice was? It collects heat from the sun in a "bankable store" that must be added to the heat to be lost before refreezing occurs.
In Year 2, according to our projections based on all previous years, volume should go to nearly zero. However, only half the ice has "negative thickness". The other half has an average thickness of about 1/2 meter. So the volume is down to about 1 km3, and the area is down about 50% to about 2 km2, while the average thickness is 1/2 meter.
In Year 3, volume is only about 0.08 km3, and its average thickness is about 1/4 meter (?). So now area is about 0.32 km2, or about 8% of the original area. 92% of the original area is a "bankable store".
And, of course, in Year 4 (or, if you prefer, in 2016 or 2017, according to our projections of "zero volume", which is really zero average thickness) it's all gone, and for one day in the year, 4 km2 has a "bankable store" to be overcome.
OK, here is my post in PIOMAS, like I promised.
Thanks for the comments from Gas Glo and others, which made me realize that, among other things, I had used the wrong terminology. So, in an attempt to sweep them all up in one answer, here's my attempt at a thought experiment.
Imagine that at Year 0 on September 15 at the minimum, you have 8 km3 volume of Arctic ice in an area of 4 km2, or an average thickness of 2 meters, with a standard deviation of 1/3 meter. Your average thickness is decreasing compared to past years at that time by 1 meter per year.
In Year 1 (or, if you prefer, 2010) you see a little more than 4 km3 of volume, a little less than 4 km3 of area, and average thickness of 1 meter. You see, about 2% of the ice (3 SDs out on the normal curve) has gone; it has "negative thickness". What happens to the water where the ice was? It collects heat from the sun in a "bankable store" that must be added to the heat to be lost before refreezing occurs.
In Year 2, according to our projections based on all previous years, volume should go to nearly zero. However, only half the ice has "negative thickness". The other half has an average thickness of about 1/2 meter. So the volume is down to about 1 km3, and the area is down about 50% to about 2 km2, while the average thickness is 1/2 meter.
In Year 3, volume is only about 0.08 km3, and its average thickness is about 1/4 meter (?). So now area is about 0.32 km2, or about 8% of the original area. 92% of the original area is a "bankable store".
And, of course, in Year 4 (or, if you prefer, in 2016 or 2017, according to our projections of "zero volume", which is really zero average thickness) it's all gone, and for one day in the year, 4 km2 has a "bankable store" to be overcome.
OK, now suppose you're in Month x, and you want to freeze some ice in Month x + 1. To make things harder, we're somewhere between 2030 and, say, 2045, January is ice-free, and we want to freeze some ice on February 15.
Well, there's not much heat coming from light from the sun, because the Arctic is in darkness. There's heat on the surface of the ocean from what's left of the "bankable store" after 3 months of lack of sunlight to replenish it, and some from currents from the south. Meanwhile, the temperature should be -30 C this time of year -- but is it?
Well, while you've been busy in the Arctic, things have been warming up down south -- and, for that matter, in the Arctic air itself. More CO2 has gone into the air from emissions, so that you're at 425-445 ppm -- and you're seeing maybe 75% of that (Hansen) in the land/ocean temperature, or 2 1/4 degrees C, with the Arctic typically double that, year-round. Also, the shallow seas off Siberia have started bubbling like a teapot with methane, doubling the effect on worldwide and Arctic temperature. And, because they're shallow, they're extra warm as a result of that "bankable store" -- and they're further south. So now we're up about 10-15 degrees C over the old days. Add another degree C from the heating of the ocean, and 3-4 more degrees from the fact that the greater energy in the winds is more frequently blowing in warmer winds from the south, raising the temperature further on average. Now add another degree or so from that "bankable store", and add a further 4 degrees before you can squeeze the salt out and turn the water into ice. You may in fact be only 5 degrees C away from being unable to turn Arctic ice into water at any time of year -- and you're probably already there in the southern Siberian Sea.
Now suppose you want to melt that water again. Because of the insulation effect, if I understand Gas Glo, without sunlight you may not be able to do it until April, assuming the air temperatures don't go above freezing before then. But when the melting does happen, because all this heating is still continuing worldwide and therefore above-zero Arctic air temps will start happening before the sun shows up, that melting will happen slightly earlier than the year before, meaning a greater "bankable store" for next year.
And note that the rate of at least some of the heating is increasing at this point (that is, from year to year). The methane, for example, is probably well less than halfway through being released, and so is still ramping up faster and faster, with a follow-on effect on air and ocean temperatures, as well as on the energy in the winds and the amount of "bankable store" in the ocean.
OK, now hopefully I've given you a better target to shoot holes in.
Posted by: Wayne Kernochan | May 25, 2011 at 19:21
oops,sorry about the duplication of the first seven paras.
Posted by: Wayne Kernochan | May 25, 2011 at 19:22
I am not sure you have understood me. Also not at all sure I want to project what may happen in 2030 - 2045 as I have enough difficulty in trying to appreciate whether we accelerate toward virtually ice free for 1 day in Sept or decelerate.
But since you are pushing me, compared to what you suggest, I think your "bankable store" is absolutely huge at the end of October, much bigger than the 1C you suggest, because of the albedo effect on all that open water (thats the 4.3M Km^2 area not your 4Km^2). However with little ice in November, the amount of heat lost to space over the winter also becomes absolutely huge because there is much less ice insulation between warm water and atmosphere slowing down the heat transfer.
It is, I think, a matter of which of these two absolutely huge figures is growing faster and I don't think I am keen on speculating past the virtually ice free in September stage. I want to see the level of acceleration / deceleration as we approach that stage (and our understanding of it)before throwing in wild (almost certainly wrong) speculation on what happens after that.
I think these two effects are the dominant
changes in the heat budgets. No doubt there are other effects as well...
Anyway, I am impressed by your ability to reach speculation of a suprisingly small "You may in fact be only 5 degrees C away from being unable to [?freeze water anytime of year?]"
Posted by: Gas Glo | May 25, 2011 at 22:18
When constructing your "bankable store", have you taken into account the thinning of the mixing layer underneath the diminishing sea ice?
Without a melting ice cap to replenish that cold layer of water, insolation, albedo changes and winds will quickly dissipate it. The net effect will be to bring the warmer, deeper layers to the surface, enhancing the melting of the remaining ice and adding extra reserves to your bank balance.
When compounding the interest in that fashion, your ledger may surprise you.
Posted by: Daniel Bailey | May 26, 2011 at 04:38
All of which illustrates why 'we'--meaning those skilled enough to do it--construct mathematical models. It's easy enough to hand-wave reasonably about various factors, but without quantifying them and specifying algorithms for how they interact, confidence in predictive value is pretty hard to come by!
None of which is particularly comforting in terms of the substantive debate. As Ray Ladbury always says, "Uncertainty is not our friend."
Posted by: Kevin McKinney | May 26, 2011 at 17:43
Rob Decker:
My point is that these charts exaggerate when the Arctic will become ice free.
These aggressive predictions of a virtually ice free arctic are counter-productive because when they fail to occur it casts doubt on the message that AGW is a problem that needs to be addressed. Instead, the failure of these predictions will lead people to say the situation is not as bad as was thought.
The comment by Robhon is very sensible. Instead of quibbling over when the Arctic becomes "virtually ice free" we should focus on the inevitability that the Arctic is headed for ice free conditions.
There will be positive and negative features to an ice free Arctic, but clearly there is change.
While dramatic, the decline in Arctic sea ice is just a side show compared to the potential damage from rising sea levels due to the melting of West Antarctica Ice Sheet and the Greenland ice sheet. These blocks of ice deserve more attention than the Arctic ice cap.
Posted by: William Crump | May 29, 2011 at 10:12
William, I don't think I quite agree with you there.
First of all, the Arctic sea ice cap is also important for the Greenland ice sheet. Where do you think all that extra heat will go once there is no more sea ice to melt?
Second: chronology. This is happening now, this is visible. Rising sea levels are too slow to grasp for most people, even at three times the current rate (which will take some time).
And to top it off I'm copying Werther's last comment:
People are in denial. They want to be in denial. That's just a fact of psychological life. We who are not in denial about this, are most probably in denial about other things. Most people are in denial about AGW, even when they accept something like An Inconvenient Truth, it just doesn't hit home enough to make significant changes.
And whether you bring it to them slow and nice, or whether you predict something that in the end doesn't come about, doesn't matter one bit. People simply refuse to inform themselves properly. Only things that are visibly changing, here and now, will break through the concrete wall of denial.
The Arctic sea ice might be that thing, although there are probably some other black swans lurking in the coalmine as we speak. We are here watching it, this is climate change (with weather patterns perhaps getting increasingly out of whack).
If the data swing back up, I'm sure we'll be the first to notice it. But right now everything is pointing down, down, down.
Posted by: Neven | May 29, 2011 at 11:22
Neven, to illustrate this on a personal level, speaking for myself. In my practical life I’m a denier too. Family life, getting along in actual society are excuses not to reshape my personal carbon footprint.
That psychological double standard stresses me through my life. Though being happy, the feeling has always been mixed since I first heard the echo’s of the Rome Club in 1971/-72. And I remember very well myself, 17 years old, darkly prophesising during biology class there would be 40 years before... To be true, I’m not completely different from that American preacher. Time is running out?
Posted by: Werther | May 29, 2011 at 12:12
Psychological resistance to understanding and accepting Climate Change as the result of Human activity is discussed in Feinberg & Willer (2011):
Apocalypse Soon? Dire Messages Reduce Belief in Global Warming by Contradicting Just-World Beliefs Psychological Science January 2011
From the ABSTRACT:
Posted by: Artful Dodger | May 29, 2011 at 14:27
"My point is that these charts exaggerate when the Arctic will become ice free."
Do they, Will? Even though I told you months ago that they are not predictions, you persist in misrepresenting them. Why is that Will?
And while you're at it, Will, when does the Arctic become ice free? You must know, because you know these non-predictive graphs exaggerate it. The only way you can know that is if you are from the future.
So tell us, Will, are you from the future?
Posted by: FrankD | May 29, 2011 at 15:06
"These aggressive predictions of a virtually ice free arctic are counter-productive because when they fail to occur it casts doubt on the message that AGW is a problem that needs to be addressed. Instead, the failure of these predictions will lead people to say the situation is not as bad as was thought."
So Will, you're telling us that in the future you are from, a bunch of people who accepted the need to do something about AGW changed their minds when my little curve-fitting graph didn't live up to its misreprentation as a prediction. Did any policy changes result, Will? What catastrophic consequences followed?
I have to say, they amount of influence I will have on the future is really trippy. I wonder if I can get future people to like disco again...?
Posted by: FrankD | May 29, 2011 at 15:13
I'll resist the almost-overwhelming temptation to deconstruct Will three further paragraphs of combined handwaving and soapboxing and cut to the chase. If Arctic Sea Ice is a "sideshow", why the hell do you waste your time posting on a blog called Arctic Sea Ice?
I can think of two reasons, neither good. So here's the final question for you, Will. Surprise me.
Posted by: FrankD | May 29, 2011 at 15:17
Frank, mate: You've done Yeoman's service in transforming PIOMAS anomalies into yearly trends. You really do not need to defend yourself against outlier views. I don't think you'll find many here that share them...
Still, everyone is entitled to their own views (see up-thread on 'Psychological resistance') just as everyone will inevitably make up there own mind. As Upton Sinclair was fond of saying, "It is difficult to get a man to understand something, when his salary depends upon his not understanding it!"
As events unfold over time, more and more people will grudgingly come around to the truth. You probably suspect we have already crossed a number of climate tipping points which will make a certain amount of pain inevitable. Remember, Mother Nature bats last, and doesn't give a rip what we say.
Posted by: Artful Dodger | May 29, 2011 at 16:16
It is likely that people will not respond to global warming until they are personally affected by or impacted by some catastrophic event. Hearing about ice loss in the arctic is not a personal, catastrophic event, nor is massive release of methane from arctic areas. Reading about tornadoes, floods, fires, melting glaciers, rising CO2 levels etc makes people aware of climate change but it does not affect them personally. There will come a tipping point when enough people have been, or can see that they soon will be, severely impacted. When that point is reached governments will finally act. We are a long way from there at this time. Melting of the arctic sea ice does not directly affect non arctic peoples and is therefore of little interest to them. When their food or jobs or houses or families are threatened they will respond. By then it may be too late. I include myself in the list of bystanders because I still go on vacation to Europe or Asia and heat a big house and have two cars. How many of us have really made the huge sacrifices that are necessary?
Posted by: r w Langford | May 29, 2011 at 18:23
SPOILER ALERT:
This will be OT, but hey it's Sunday ;^)
Bob, the human capacity for empathy is what empowered photo-journalists covering the Vietnamese conflict to bring about an end to the war. They achieved this by influencing Public Opinion over the course of about 5 years.
But there are real effects of the loss of Arctic Sea ice already.
The heavy snow this Winter in Eastern North America was a direct result. Now, tornado alley storms are supercharged by outbreaks of cold Northern air penetrating deep into the U.S. There it mixes with a Gulf airmass carrying 8% extra water vapor (storm fuel), due to +2F SST anomalies in the Gulf.
Not impressed yet? You know there was a hole in the Arctic Ozone layer this Spring, right? By March 29, 2011 over 40% of Stratospheric Ozone had disappeared over the U.K. This is a direct result of green house gases trapping OLW radiation near the surface, which causes the Stratosphere to cool, and leads to chemical reactions which destroy Ozone. This can not happen at the higher temperatures usually present in the Arctic Stratosphere, but did this year for the first time, as was predicted would eventually happen. The Arctic Ozone hole will only get deeper and wider as GHG levels increase without bound. Canada (and any other Northern Country) is Ground Zero for the Ozone hole...
What's your personal tolerance for UV? How about your Neighbor? How about Risk? Don't you think there's enough reason already to act? Isn't it irresponsible not to act? And it all begins by Demanding Less...
Posted by: Artful Dodger | May 29, 2011 at 19:23
Artful, most of us are not being impacted catastrophically yet, put another way we can use sunscreen for now. When food is significantly limited by high UV levels that will be catastrophic but I digress from the topic. Sea ice is but a side show to the general public. Don't confuse this to mean that I think it isn't driving climate change. Nor does it mean I am not intensely interested in it but most people I talk to yawn when I bring up the topic then get into their SUV. Hope I don't offend anyone I am presenting an opinion as to when the tipping point of serious public action will come.
Posted by: r w Langford | May 29, 2011 at 20:22
FrankD:
Why not provide a chart or graph that indicates when you estimate the Arctic will be virtually ice free for each month so there is no confusion?
Sure it is fun to watch the dramatic change in the Arctic and I enjoy the strong response, but I doubt that seeing an ice free arctic, even for a week, is going to cause people to make changes.
As a baseline question, what changes would be necessary to get the Arctic back to where it was in 2000 and how many years would it take for this to happen and what is it going to cost?
In the mean time, like it or not, the opening up of the Arctic to human exploitation by the removal of the ice is likely to boost the worldwide economy.
I also do not think your analysis of the impact of the diminished ice cap includes all impacts. I have seen some analysis which suggests that a diminished Arctic ice will cause a loss of coastal ice cap areas, but will strengthen the higher elevations of the Greenland ice cap as it could result in an increase in Arctic humidity which could cause an increase in precipitation at the higher elevations of the Greenland ice cap which remain well below the melting point and well below 80 degrees north.
I enjoy the discussions here, but I doubt that the more aggressive predictions of a virtually ice free Arctic by 2013 or 2016 will come to pass.
Posted by: William Crump | May 29, 2011 at 21:02
Wow, all, lots happens when I'm away. Let's see if I can provide some not too banal responses.
Gas Glo, I'm sure I have made lots of SWAGs. My concern is more to try to zero in on the most likely combination of factors rather than to be conservative about those with a great amount of uncertainty, because I think that in the past that has led to too much underestimation of the effects (esp. volume) we are seeing now.
I would raise a question about one of your statements, that there would be a huge outflow of heat from water to space. What I am arguing, I think, is that at, say, right now, we should see air temps in November that are higher than in the past, because of warmer air from down south, and therefore the outflow of heat from the water might be less than you think. And, as time goes on, and this feeds into yet warmer temps down south, the same applies to each successive month. Beyond that, you know way more than me.
Daniel - no, I hadn't taken that into account. I assumed that it would be counteracted by accelerated melting of the Greenland ice caps, which would release a flood of additional cold water, some of which would find its way to the Arctic. For that reason, Hansen in his latest paper (cite?) sees a limit of about one meter/decade in worldwide melt, as the rest will go into slowing the rise in temps. However, I'm not sure his analysis takes into account that at some point fairly soon we will have to slow our emissions of pollutive aerosols (dust, black soot), which will drive the temp increases back up again.
William and Neven: Actually, I'm concerned about Arctic ice precisely because I see it as affecting Greenland and then the Antarctic, sooner rather than later. The effects on Greenland, as I understand it, are that blocking ice that "latches onto" the sides of the beyond-sea-level glacier flow or that extends to the opposite shore, "pushing back", is melted, speeding up glacier flow and the net loss of Greenland ice. Many glacier outlets are towards the north, where the ice has yet to melt even in summer. So, as we see "islands" like Petermann begin to break off more, that means the flow of ice behind is speeding up; and the more Greenland is sea-ice-free in summer and then year-round, the more glaciers flow faster year-round; and then the whole process moves under the bottom of the land ice and another speedup occurs.
Meanwhile, the overall temp rise in the ocean from Arctic albedo effects reaches down to the Antarctic and moves the circumpolar warm current closer, eating at the ice shelves there and making their glaciers flow faster -- as is already happening, according various papers. This greases WA (?), and once they go EA glaciers start to slide, both from the current and the lack of blockage from the lower EA ice.
William, your point about the increased humidity/snow precipitation is taken account of in recent studies of the ice cap, which show that so far the overall effect is an acceleration of the Greenland ice cap net melting at the rate of doubling every decade, as the rise in precipitation is more than counteracted by the rise in the elevations that remain below the melting point. I note this only in case someone else was confused.
And because of the feedback effects of the melting and CO2 release that have already occurred, the latest Hansen estimate as I understand it is that it will take thousands of years to take the CO2 level back to 350 ppm -- which would take the Arctic back approximately to where it appeared to be in 2000 -- and doing it in only thousands of years would be hard to achieve unless we reduce our fossil-fuel and related emissions of CO2 to 10% of their level as of right now, and do it in the next 5-9 years, and then keep it that way for thousands of years. Cf. climateprogress.org's citation of Hansen. Again, I am noting this for others to correct me.
Thanks again for all the corrective info, and apologies for any misstatements - Wayne
Posted by: Wayne Kernochan | May 30, 2011 at 01:23
Artful Dodger wrote:
This reminded me of the explanation I heard for the cold European and North American winters that were tied to low sea ice concentrations in the Arctic so I decided to look it up and see what parallels there are.
Expanding off of their presentation at the European Geophysical Union:
http://neespi.org/web-content/meetings/EGU_2009/Semenov.pdf
... the authors argue in:
Vladimir Petoukhov and Vladimir A. Semenov (Nov 2010) A link between reduced Barents-Kara sea ice and cold winter extremes over northern continents, Journal of Geophysical Research, Vol. 115, D21111
http://eprints.ifm-geomar.de/8738/1/2009JD013568-pip.pdf
... that low ice concentration in the Barents-Kara sea results in a high pressure zone, a reversal of the direction of atmospheric circulation in the region, and in essence an Arctic corridor bringing Arctic air into Europe and colder temperatures into Southern Canada and parts of the United States.
A climatologist does a brief review of the ideas behind the paper here:
Why has this winter been so cold in Europe?
Andy Russell, 2011-01-06
http://andyrussell.wordpress.com/2011/01/06/why-has-this-winter-been-so-cold-in-europe
However, over much of the Arctic the ice melt has begun late, there was a strongly positive rather negative Arctic Oscillation Index, and while parts Siberia has seen unusually high temperatures and Northern Canada usually cold temperatures in April:
Slow start to summer sea ice melt
May 4, 2011
http://nsidc.org/arcticseaicenews/2011/050411.html
... the lows didn't extend very far into the United States.
Please see:
NASA: Globe In April Was 4th Warmest On Record
2011-05-19
http://weatherdem.wordpress.com/2011/05/19/nasa-globe-in-april-was-4th-warmest-on-record/
As such the parallels with cold European and North American winters seem to go only so far, at least from what little research I have done. Do you know of a good analysis that ties the tornado outbreak to global warming and the conditions in the Arctic?
Posted by: Timothy Chase | May 30, 2011 at 04:08
Hi Timothy. Yes, Joe Romm posted recently on the relationship between Climate Change and Tornado activity:
Tornadoes, extreme weather, and climate change
Hi Bob: try purchasing 1 less tank of gasoline this month!
Cheers, everyone!
Posted by: Artful Dodger | May 30, 2011 at 06:42
For Gas Glo:
I'm not clear how Romm's post relates to my "thought experiment" up above, but he does note that the Met Office projections do not include methane release, and a subsequent post on "deniers" notes that winter temps should increase by more than summer temps throughout the world -- and that the data shows this is already happening. So I continue to view Feb. temps close to the point of ice not being able to freeze as perhaps the likeliest of all scenarios by 50 years from now at the latest.
Posted by: Wayne Kernochan | June 02, 2011 at 21:00
Some of you may not be aware of NSIDC's "Icelights" blog. A recent entry there is well worth reading for immediate consequences on a local level along the coast of Alaska:
Sea ice and the Arctic coast | Katherine Leitzell | NSIDC Sea Ice blog | May 23, 2011
Posted by: Artful Dodger | June 05, 2011 at 19:29
Great link, Dodger! These people are not only facing some of the most harsh of climate, they also have to move the whole community inland to get away from the receding coastline, 10 meter pr. year, that's really some challenge for poor citizens! Most likely the state of Alaska doesn't find it worthy to build molos to defend the land?!
Posted by: Christoffer Ladstein | June 05, 2011 at 21:16
Per NSIDC
June 6, 2011
Low ice extent in May, but summer melt will depend on weather
Arctic sea ice extent for May 2011 was the third lowest in the satellite data record since 1979, continuing the long-term decline. During the month of May, sea ice declined at a near average rate, while air temperatures in the Arctic remained generally above average. Although ice extent is low for this time of year, ice extent at the end of summer largely depends on weather over the next few months.
...Arctic weather in the next few months will be a critical factor in how much ice remains at the end of the melt season. New research led by James Screen at the University of Melbourne shows that the storms that move northwards into the Arctic from the lower latitudes during summer strongly influence sea ice extent at the end of summer. Years with dramatic ice loss, such as 2007, have been associated with comparatively warm, calm, and clear conditions in summer that have encouraged ice melt. Summers with slow melt rates are opposite and tend to be stormier than average. The number of storms influences how warm, windy and cloudy the Arctic summer is.
http://nsidc.org/arcticseaicenews/
Wayne:
Thanks for the updated information, particularly with respect to Greenland and the impact of reduced Arctic ice cover.
The Hansen information is rather discouraging. Are there other sources that challenge Hansen's analysis?
Posted by: William Crump | June 06, 2011 at 22:54
@ William
As far as Hansen, remember that it is not yet published, so it hasn't yet undergone the full peer-review process. After that point you will see subsequent papers either confirming, amending or refuting it. So it takes time. In the meantime, Hansen 2011 remains essentially a "white paper". Take it with a grain of salt, but also a shot of tequila, as his papers largely endure.
You also might want to read these recent reports:
1. Effects of Climate Change in Arctic More Extensive Than Expected
2. Today's Carbon Release to Atmosphere 10 Times Faster Than in the PETM
That last one is a real stunner. Like a triple shot of your liquid brain-death du jour followed by a 2x4 upside the head.
Posted by: Daniel Bailey | June 07, 2011 at 04:42
Daniel Bailey:
The 10X carbon release compared to PETM is a very interesting article.
If the PETM carbon release was due to a burp of CO2 from a warming ocean (somewhat like what happens to a beer or carbonated soft drink as its temperature rises)is it possible that a warming ocean in current times could result in a similar CO2 burp or is the current ocean concentration of CO2 sufficiently below "burp" levels that this is not likely to occur?
Is there an analysis of how much warmer the oceans would have to become before a methane burp from Methane clathrate would occur?
If the Hansen estimate of our ability to affect future CO2 levels is correct, and we would have to shut down 90% of the world economy to get CO2 back to 350 ppm, then maybe we are better off just gradually moving cities inland and building better seawalls.
Posted by: William Crump | June 07, 2011 at 22:28
Daniel Bailey:
Based on the Hansen report, if we gave up heating and cooling our homes and stopped driving cars on a world wide basis as of tomorrow, could "we reduce our fossil-fuel and related emissions of CO2 to 10% of their level as of right now"?
Is there a more realistic estimate of what can actually be done to reduce carbon emissions without tanking the world-wide economy?
I would read the Hansen paper as proof that a target of 350PPM is not achievable.
Is there another level, say 450PPM that is possible and would mitigate some of the expected sea level and climate disruption from the additional heat in the atmosphere?
The Arctic ice loss may be unstoppable, but in and of itself, it is likely to be a greater concern for polar bears and ice dependent wildlife than it is for humans.
While the topic is Arctic ice for this posting, ice loss from Greenland and the WAIS are more troubling an issue.
"We derive mass changes of the Greenland ice sheet (GIS) for 2003–07 from ICESat laser altimetry and compare them with results for 1992–2002 from ERS radar and airborne laser altimetry. The GIS continued to grow inland and thin at the margins during 2003–07, but surface melting and accelerated flow significantly increased the marginal thinning compared with the 1990s. The net balance changed from a small loss of 7+-3Gt a–1 in the 1990s to 171+-4Gt a–1 for 2003–07, contributing 0.5mma–1 to recent global sea-level rise. We divide the derived mass changes into two components: (1) from changes in melting and ice dynamics and (2) from changes in precipitation and accumulation rate. We use our firn compaction model to calculate the elevation changes driven by changes in both temperature and accumulation rate and to calculate the appropriate density to convert the accumulation-driven changes to mass changes. Increased losses from melting and ice dynamics (17–206 Gt a–1) are over seven times larger than increased gains from precipitation (10–35 Gt a–1) during a warming period of ~2 K (10 a)–1 over the GIS. Above 2000m elevation, the rate of gain decreased from 44 to 28 Gt a–1, while below 2000m the rate of loss increased from 51 to 198 Gt a–1. Enhanced thinning below the equilibrium line on outlet glaciers indicates that increased melting has a significant impact on outlet glaciers, as well as accelerating ice flow. Increased thinning at higher elevations appears to be induced by dynamic coupling to thinning at the margins on decadal timescales."
Posted by: William Crump | June 07, 2011 at 22:53
I find Greenland to be defined as part of the Arctic, and I trust Neven and the others in here to agree upon that!
Still, if people are to get really worried about these changes, the sealevel have to rise FASTER than just 1-2 millimeter a year...
Posted by: Christoffer Ladstein | June 07, 2011 at 23:27
BTW, talking about Greenland, have you noticed the skyrocketing temps there the last couple days? Very close to 20 C, after being held in a cold grip for weeks, are we to expect they're facing severe local floodings? Up north in Norway that "phenomenen" occured today due to the russian heatwawe, paying the Lapland of Norway a brief visit!
You noticed that the Siberian Russia already have more than 6000 km2 burned down in forestfires this season, much more severe than last year! And the summer just started....
Posted by: Christoffer Ladstein | June 07, 2011 at 23:35
Christoffer,
The drag in this all is that there isn’t any specific threat that is going to make a lot of people aware at the same time and at the right moment. The engineering riddle is that ‘we’ can control nature, even when sea level rises 50 cm (imagine Greenland having lost 200 KKM2, 2050).
But sea level isn’t the main problem (though I’m concerned living -1 m below SL). It is the complex of intertwining climatic change, that will mess up most traditional agricultural systems. Moreover, cheap energy supporting our technical capacities is running out, so ‘we’(that is most of our kin) won’t be able to clear the mess.
But 'we'´re not going to contribute that to AGW. 'We'´re going to miss that being covered by our main media. An example may be that we´ve noticed the tornado busts the US took, but there´s little covering of the rain drama in Colombia, now lasting for almost a year.
You see, it´s not a matter of Great Disasters, but of relatively fast, fine-scaled degrading ecology. Soon after our fossil-fuel energy potential is ending, that will have the main impact.
Posted by: Werther | June 08, 2011 at 00:07
William,
Hansen certainly did not suggest throwing away cars and all of moving back into caves. Why do you make such an absurd claim? The suggestion is to move into renewable energy (Hansen likes nuclear). Read the threads on Skeptical Science which describe how to generate all energy from renewables. We can have a similar standard of living without the carbon dioxide.
Posted by: michael sweet | June 08, 2011 at 02:33
@ William
Re: Clathrate releases
There is some evidence clathrate releases and destabilization may already be underway.
Re: Arctic Sea Ice loss
The seasons of the northern hemisphere are predicated on having a functional planetary air conditioning system. We lose that functionality than any likelihood of retaining our "sweet spot" goes bye-bye.
@ Werther
Re: Climate change & agriculture
This is a good read for an idea of changes now in the pipeline.
Posted by: Daniel Bailey | June 08, 2011 at 04:14
OK, I realize this is off-topic, but I'm not sure where else to ask:
What, according to Neven's daily graph, is going on with Antarctica temperatures? More than 20 degrees C above normal over much of the continent? Does that mean that, as it seems, some of the Antarctic peninsula is above 0 degrees F, or even above freezing? Is this in the range of normal variation in early winter? Context, anyone? As in, please talk me down ... - w
Posted by: Wayne Kernochan | June 08, 2011 at 20:00
"Is some of the Antarctic peninsula above 0 F, or even above freezing?"
See this image, which includes absolute values, not just the anomaly:
http://www.esrl.noaa.gov/psd/map/images/fnl/sfctmpmer_01b.fnl.html
Yes to the first, no to the second, it would appear. I'm not sure how normal it is, but I doubt it's all *that* extraordinary.
What say you, more-informed persons?
Posted by: Kevin McKinney | June 08, 2011 at 20:52
OK, I'll show my lack of statistical skills even further. I went through their anomalies for June 5 (the latest date I could) from 1980 to 2011 and found nothing as extreme (that is, on the continent of Antarctica itself). Always, positive anomalies were less extensive and usually lower, and negative anomalies were more extensive. Interestingly, there seemed to be a break around 1996, before which the mean seemed to average lower than after 1996.
Posted by: Wayne Kernochan | June 08, 2011 at 22:27
Wayne:
I have also been curious about "what's going on down under" for a while, but we have to remind ourselves that it's winter there now, and Antarctica is mildly speaking damn cold, even at summer, so even 20 C above normal must mean 10-30 below freezing, except the coastal areas stretching upward to Chile/Argentina.
http://en.wikipedia.org/wiki/Climate_of_Antarctica
OTOH, extreme positive anomalis also took place in the Arctic during "our" winter, and this is the present future, at both poles, as decribed rather frequently, also by IPCC.
Posted by: Christoffer Ladstein | June 08, 2011 at 23:09
Interesting observations, Wayne. Perhaps this is something to keep a bit of an eye on.
Posted by: Kevin McKinney | June 09, 2011 at 18:35
Arctic Sea Ice Volume Anomaly, version 2 has been released as of June 15, 2011.
http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/
Posted by: Artful Dodger | June 16, 2011 at 04:06
Frank, Wipneus, Larry: You'll appreciate this (as we appreciate your popular requests :^)
You are required to fill out a User form to receive a link to the Data.
Posted by: Artful Dodger | June 16, 2011 at 04:43
Thanks for those, Dodger (luv the new volume anomaly graph).
Any progress on what we discussed?
Posted by: Daniel Bailey | June 16, 2011 at 04:47
Arctic Sea Ice Volume Anomaly v2 Validation
Aiming for June 21, Yooper!
Wipneus, recognize these diverging curves? I think we have our answer now why Larry's numerical data doesn't match Frank's induced data... It's very similar to your plot of differences.
Posted by: Artful Dodger | June 16, 2011 at 05:34
Hmmmm..... I tried the link to the raw PIOMAS data and it appeared to be broken:
http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/data-2/
Posted by: Bfraser | June 16, 2011 at 08:12
Try this one:
http://psc.apl.washington.edu/wordpress/research/projects/arctic-sea-ice-volume-anomaly/data/
Fill the (optional ) data; click on "send" and a download link appears at the bottom.
Posted by: Wipneus | June 16, 2011 at 08:49
Dodger:
Larry's numerical data appear to have been lifted from a data set very similar to the now released version 2. The September values are very close to those from Larry: within 100 km3 or so.
Posted by: Wipneus | June 16, 2011 at 12:06
Eh?
So, if I have got this right, then PIOMAS goes off-line for 6 weeks, double-checks its data, then comes back and publishes the UNcorrected data as the main graph?
So instead of a fall of 3.6 k cubed per decade, as per the old dataset, or 3.5 k cubed per decade, as per the new corrected dataset, we have a fall of only 2.8k cubed per decade... er, unless you check the small print, which tells you that this is wrong, and too conservative.
I hope FrankD, that you can have a look at this issue before attempting to update your fine graph of the actual monthly values.
I'm surprised that PIOMAS hasn't noticed that this graph makes the situation much more clear than their own presentation of just the data anomalies.
Finally, ignoring all of these quibbles, it's also worth noting that volume has just nose-dived again, at around the same season as it did in 2010.
Posted by: idunno | June 16, 2011 at 12:12
So it appears they have gone from showing the graph of the adjusted series to the unadjusted series with error bars.
They did say "To be sure, this is not mea[n]t to create a “better” ice volume estimate but rather to test the sensitivity of the ice volume trend to potential systematic errors in the model estimates."
However their talk on the possible systematic errors seems like it could be confusing me.
"Most in situ measurements are based on sonar, which uses the first return from the sound that bounces off the bottom of the ice. The creates a bias in the estimate that is small when the ice is smooth and worse if the ice is rough. Because thick ice is often very rough, ice thickness estimates from in situ measurements may actually be biased higher for thick ice than for thin. It is therefore not totally clear whether the fact that PIOMAS tends to underestimate thick ice is a model or a data problem."
Talk of using 'first' return could mean the in situ measurements give a value that is below average. (Or maybe signal does not return if at a bad angle and only returns from lowest point.) Does biased higher for thick ice mean the in situ measurements give a value above actual?
If so, it would appear that the adjusted figures may be too high.
That thick ice problem will be more prevalent in early years. I suspect from what they are saying that in later years the adjusted trend may be a better estimate of volume.
Combining these two the adjusted trend may be a little too steep but the volume at the end may be a little lower than the adjusted trend (which is the lower of the two at this point).
Am I interpreting this correctly? If so, should we, or someone, try to create a better trend that moves from 100% unadjusted series at 1979 to 100% of 1% below adjusted trend at 2011? Then run a gompertz fit through that.
Posted by: Gas Glo | June 16, 2011 at 12:26
What they're saying is that when comparing the PIOMAS model to sonar measurements, in areas of thick ice, sonar gives values that are even thicker than the model.
There are two possible reasons for this:
1) PIOMAS model is understating the thickness of these regions.
2) The sonar is overstating the thickness of these regions.
The potential data issue with the sonar results is that these readings are taken by "pinging" upwards from underneath the ice and listening for the start of the echo - sonar thus measures the thickness of the deepest part of the ice, rather than the average thickness. Consequently, in areas of thick ice where the ice undersurface is very rugged, sonar measurements will overstate thickness. It's thus quite plausible that PIOMAS is correctly modelling the average ice thickness, and that the discrepancy with the sonar results is an error in the sonar measurements rather than in the model.
The reverse error may (or may not) be occurring in areas of thin ice: in these areas, sonar gives values that are even thinner than the model. Once again, you have the choice of whether to believe the model or the sonar measurements, and it's not a given which of them is more accurate.
However, it's important to look at the actual scatter plots, here:
http://psc.apl.washington.edu/wordpress/wp-content/uploads/schweiger/ice_volume/validation/Fig2.png
http://psc.apl.washington.edu/wordpress/wp-content/uploads/schweiger/ice_volume/validation/Fig03.png
They're being too hard on themselves when they say "PIOMAS tends to overestimate thin ice" - I don't think it does. There is actually very little systematic bias at the thinner end of the graph near the origin, and the scatter is symmetrical about the 1:1 diagonal line (in green). The asymmetry is almost all at the thicker end of the graph (top right), where the PIOMAS model gives lower values than the sonar measurements, and the points thus almost all fall below the 1:1 diagonal line.
The only place the supposed "underestimation of thin ice" shows up is in Fig02.png, the calibration data set, which has almost no points at all under 1m thick. Moreover, I suspect that because the calibration set is used to calibrate the average thickness estimates of the model - that's what calibration is for! - then the discrepancy at the top end must necessarily lead to an equal and opposite discrepancy at the low end for the points within the calibration data set. When you look at Fig03.png, which is based on independent measurements, i.e. not those used to calibrate the model, there is no discrepancy at all at the low end: i.e. it seems that PIOMAS is indeed correctly modelling thin ice, and that the discrepancy is restricted to thicker ice.
As for adjustments, the "adjusted trend" is what you get if you assume the sonar measurement is 100% accurate, and the discrepancy is all down to errors in the PIOMAS model. As I read it, it simply puts a linear regression through the scatter plot, and uses that to convert the PIOMAS model points into the best-guess of what the sonar measurement would show.
However, as noted above, the discrepancies are not linear - they predominantly affect the top right part of the scatter plot, in the thicker ice areas, exactly the places where the sonar measurements may be inaccurate. Performing a simplistic linear adjustment will have the effect of increasing the modelled thickness in regions of thick ice (to match the possibly-wrong sonar data) and decreasing the modelled thickness in regions of thinner ice - where there's no real discrepancy in the first place!
I guess the ideal solution would be to fit some kind of curve through the scatter plot and selectively adjust the data from thicker ice to match the sonar, but it's only worth doing that if you're confident in the sonar data in the first place!
All told, I'm sure this is why they plot the unadjusted data on the front page. The adjustment isn't required at all for current years, since there's so little thick ice that needs adjusting for - and the adjustment even for earlier years may be based on inaccurate sonar data.
Posted by: Peter Ellis | June 16, 2011 at 13:21
TLDR version:
1) Current PIOMAS ice volume estimates seem likely to be accurate.
2) Estimates for previous years may be underestimates, depending on how literally you take sonar measurements in areas of thick (rugged and ridged) ice.
3) If you correct for (2), you'll get a steeper trend, but it's not at all clear whether there's a real problem that needs correcting for.
Posted by: Peter Ellis | June 16, 2011 at 13:30
Thank you, that has certainly improved my understanding of it.
Posted by: Gas Glo | June 16, 2011 at 14:51
I have calculated monthly averages with the new data. Here are the plots:
September ice fitted with several curves:
http://img194.imageshack.us/img194/4402/piomastrnd1.png
No clear winners with regard to correlation coefficients: exponential, logarithmic, Gompertz and quadratic perform similar. The logarithmic curve fits especially good with the recent years, so maybe that is a point to remember.
All months fitted with an exponential curves, are here:
http://img42.imageshack.us/img42/2294/piomastrnd2.png
Posted by: Wipneus | June 16, 2011 at 16:17
Of course, the Big News out of this Exercise is the Error Bars. This is the first time PSC has provided a confidence interval for modeled Sea Ice thickness.
Drum roll please...
+/- 0.10 m Basin wide, with best fit in the Center. Bingo!
This pre-press Paper was released yesterday and will be published later this year in Journal of Geophysical Research – Oceans:
Uncertainty in Modeled Arctic Sea Ice Volume (62 pages of Answers to all your burning Questions ;^)
Posted by: Artful Dodger | June 16, 2011 at 17:28
The following is a quote from page 31 of Schweiger et al. (2011):
DRA above means "Data Release Area" for US Submarine Cruises, which are all within the Beaufort Sea and Central Arctic Basin (see Fig.2 on page 49).Of course, this is the main area of interest because we are already past the point in time where the other basins melt out consistently before the end of Summer.
Going forward, I expect CryoSat-2 data to be at least as reliable as IceSat data for Beaufort/Central Basin.
Posted by: Artful Dodger | June 16, 2011 at 19:06
I've feeded zunzun.com with the lowest volume of each year and let it choose best curve fit from its internal set of +500 non linear and +8000 linear function types. First 20 results did not select a linear function instead first 6 results even have a sharper decline than Frank's graph.
This function won:
n^2 = A + Bx^2 + Cx^4 + Dx^6 + E/x^2 + F/x^4 + G/x^6 + H/x^8
See here: http://goo.gl/NcnLI first 20 plots plus absolute error.
Given all the feedback effects, assuming nature behaves in a linear fashion sounds ridiculous to me.
Posted by: Arcticio | June 16, 2011 at 20:54
Funny. I just walked in thinking if one could do Fourier transformation to sea ice extent or volume series, and tried to find best fit with least frequency components. And what (if any) forecasting value this experiment would have.
Twenty years from my FFT days, so only vague musings.
Posted by: Janne Tuukkanen | June 16, 2011 at 22:26
This function won:
With no less than eight arbitrary parameters I'm not bloody surprised! As has been famously observed, with four parameters you can fit an elephant, and with five you can make him wiggle his trunk.
http://java-srv1.mpi-cbg.de/publications/getDocument.html?id=ff8080812daff75c012dc1b7bc10000c
Posted by: Peter Ellis | June 17, 2011 at 01:20
I was going to refrain from ragging on the 8 parameter fit, but with Peter breaking the ice (so to speak), that fit is silly. The arctic ice is a physical system and any simplified model of it has to have a physical rationale. One can make such a rationale for a Gompertz, logistic or exponential - maybe a couple others. In the absence of evidence that one is outside a linear regime, one would start there - however, we certainly have evidence of that in this case.
Posted by: Greg Wellman | June 17, 2011 at 02:29
Lodger - re your "I think we have our answer": The trend difference is exactly as expected - when we were surprised by the different data Dr Zhang sent Larry, I noted that the new data started lower and finished higher, with the difference between the two sets being in the 75.8 km^3 per year (for September data only). So the difference of ~800 km^3/decade is spot on. We do indeed have our answer.
I agree with Peter Ellis' remarks about the scatter plots - while the greater error is in the thicker ice, there's 9/10's of bugger-all ice above 3 metres thick left, so overall I would suggest that the new version is possibly overestimating the total volume.
Wipneus - great job on being so quick to run the new data into monthly curves! Fascinating that even though the trend is significantly flatter, the intercept for September is only two years later...
Posted by: FrankD | June 17, 2011 at 11:44
My PIOMAS journey started with trying to extract absolute volumes from their anomaly graphs to analyse them. Since PSC now publish this data, there is no requirement for me to continue doing so. Yay!
I had spent a fair bit of time over the last month trying to hammer out an article for Neven on confidence limits on ice-free periods based on PIOMAS volumes. Since that baseline data has now changed, and PSC now show error bars and have published a 62 page treatment (eeep!), that article needs a major rework. I don't really have the time or patience to do-over for now - PSC have now liberated enough data that better statisticians than me can play to their hearts content. So this will be my last "expert" (I use the term loosely) comment on PIOMAS. I'll happily settle back to spectator for now.
For what its worth, on their old data set, I found that a brief first season of ice-free-ness was succeeded by a very rapid expansion of that window - after the first ice free "moment", it expands to a full three months after only 3 years (using a quadratic trend) or 8 years (using linear). This expansion occurs at all statistical confidence levels (from -2SD to +2SD). That expansion slows as the melt recedes through Spring and the freeze comes ever-later through Autumn. Finally, when there is only Winter coverage, the pace accelerates again and a perennial ice-free state emerges quite quickly. The whole process takes between 16 years (quadratic) and ~40 years (linear). I hadn't got around to Gompertz analysis.
I assume the new data set will yield much the same qualitative results, although with the timeframes stretched a little. If no one gets there first, I might have another hack at it when I have more time later in the year. But don't forget to check the archive of this page in 2070 and see how that prediction stacks up!
:-)
Posted by: FrankD | June 17, 2011 at 12:17
That's a bummer, Frank! But thanks a lot for your efforts so far! This was (and is) a big subject of interest on this blog, mainly because of your work. And let's not forget Wipneus (I'll use that graph of yours later today) and Larry Hamilton.
Posted by: Neven | June 17, 2011 at 13:16
I have put up a new post for the new version of PIOMAS.
Posted by: Neven | June 17, 2011 at 14:33
Frank, agreed on the resolution between the two data sets. Nudge's as good as a wink, wot?!
In addition, I'd like to encourage you to publish your results. For one, I know you are the only Commentator that has deduced that Sea Ice has a natural thickness minimum threshold at around 1.1 m.
This is an important result! This year, End-of-Winter Sea Ice thickness in vast parts of the Beaufort Sea and Central Arctic Basin was only 1.3 m (as measured by the Alfred Wegener Institute / Polar5 / EM Bird).
This is a 20 cm decline over 2010 thickness, and 30 cm less tha 2009. If we have another Winter like 2011, then 2012 will see a major collapse in the Central Basin. That would be a additional 2+ Million km^2 decrease in SIE.
I suggest that you just gut the stuff that's been obsoleted, and publish that puppy!
--
Cheers, mate!
Posted by: Artful Dodger | June 17, 2011 at 16:13
The trend of trends.
Could we not test these extrapolations? We could produce a trend from data between 1979-2000, and write down the zero SIE date. Same for 79-01, 79-02, ... For the linear this could give something like 2100, 2080, 2050, ... And for the exp 2060, 2040, 2030. Then select the curve with the smallest deviation.
Doh! There must be deviation characteristics for each curve by its very own mathematical nature. But some way to compare these there should be.
I'm sure something like this the professionals of the field do every day.
Posted by: Janne Tuukkanen | June 18, 2011 at 13:46
Very interesting PIOMAS data, http://www.creditratings101.com/free-fico-score/
Posted by: William Ryall | October 18, 2011 at 09:54
What a weird spammer. Time to wield the broom!
Posted by: Peter Ellis | October 19, 2011 at 00:10