Thank you. This is very interesting. It’s only yesterday that I read some articles and blogs by deniers dealing with Antartica, which is, according to them, the biggest proof that climate science is wrong, because the ice is not thinning and is, in some places, even getting thicker. Of course, I do not believe this. I do not believe anything from these people. Best regards, Will
[Response: Yup. It’s easy to focus on a place where we have the least information, to try to declare such information wrong. Of course, we do have enough information: the rate at which Antarctica is losing mass has been increasing along with Greenland. The rate of increased loss is an additional 14 billion tons/year, each year. See e.g. panel b in Rignot’s figure (site linked in the article above, figure here).–eric]
How is this likely to affect the interpretation of ice cores, if at all
[Response: Not much – this kind of ice is very different to compacted snow (no air bubbles for instance), and the isotopic values will be much more homogeneous than the rest of the core. So if they found this kind of ice, they’d know it. It might impact where people might drill though. – gavin]
Comment by Gordon Morrison — 10 Mar 2011 @ 9:41 AM
Actually, it doesn’t seem odd at all that water would flow uphill in these conditions. Makes sense to me, anyway.
But what I don’t understand (depths of ignorance, freely confessed – probably a stupid question) is this: are the lateral forces on the mountain range in equilibrium? That is: is the ice exerting a force through the mountains, in the direction of whichever side of them has the more mobile ice forms, or not? If so, is the heat generated by that non-trivial?
Comment by Jaime Frontero — 10 Mar 2011 @ 10:37 AM
[Response: You are correct. A straight line in these figures (with negative mass balance) would be a constant loss of ice, the slope indicates that the loss is increasing over the last twenty years. – gavin]
In 2010, the sea level contribution of Greenland and Antarctica is 1.67mm/y
The contribution of ice caps and mountain glaciers is 1.25mm/y (402 gt/y in 2006 with 12 Gt/y^2 acceleration).
The sum is about 2.9mm/y in 2010 and 2.52mm/y in 2006.
The average is 2.7mm/y.
The altimetric sea level for this period is about 3mm/y.
So, the steric sea level is only 0.3mm/y for this period.
With regard to the question of #7 regarding the steric sea level change in 2010, another term to add into the mix might be interannual variations in land storage. Also, when calculating a term in a budget as a residual, it is important to propagate the errors through the calculation. There may be a bit of a range on the steric sea level change estimate in this case.
Hansen conjectures exponential increase, rather than quadratic, but over the short timescale of the data, exponential and quadratic are indistinguishable. So Hansen’s constant doubling time idea is not ruled out.
[Response: Any extrapolation based on fitting an arbitrary function is problematic and will inevitably diverge from reality sooner or later – I would much rather have an estimate based on physics. But the meantime, these extrapolations need to be treated rather carefully. – gavin]
In 1992 the sea level rising was about 3mm/y.
It’s the same that the 2010 rising.
In 1992 the “melt” rising was 0.5mm/yy, so the steric was 2.5mm/y.
In 2010 the melt rising is (selon Rignot et al) 2.9mm/y.
So the steric is 0.1mm/y (OK there are error bars …))
If this steric rising is decreasing this is because (in the middle term)the radiative budget TOA is also decreasing.(but perhaps the climatic variability could help us?)
This is very “inconvenient”, I think.
And I don’t think that land storage variations can explain this.
But maybe Gavin could give a response?
“On ne sait jamais…” [Response: I think you’re ignoring the uncertainties on all these numbers. If the new ice dynamics numbers make other estimates necessarily smaller, or larger, but still within their original uncertainties, this means ‘no detectable change’. Try those numbers again, but include the uncertainties as given in the published literature, and *then* see if there is anything that requires an ‘explanation’.–eric]
Just a sligthly off-topic and technical question (I can’t get access yet to the article, must check in my lab but I have doubts) : which wavelength (and instrument) did they use ? I read on the profile a 2000m penetration, which is very impressive considering we are dealing with ice (our own small hand-held radars can barely get to 20 meters …)
(Recaptcha : from turequa. Lord Inglip knows where it comes from …)
[Response: It’s all about wavelength of course, when it comes to penetration. For the bit of ice radar work I’ve done, it’s 5 MHz frequencies. Bell is using higher frequency, but has a lot more power than our little home-built devices. These instruments are all custom made, in Bell’s case I would guess they are using instruments built by the U. Kansas engineering group (see their web site https://www.cresis.ku.edu. From the paper. “150 MHz ice penetrating radars with bandwidths of 15- 20 MHz produced high-resolution images of the internal structure of the East Antarctic ice sheet.”–eric]
Familiarity with its molten state makes it easy to forget that water is a mineral- the first of the oxides in Dana’s classic System of Mineralogy.
And like all minerals abundant enough to form rocks, it is encountered in a variety of textures, including dynamically generated ones, termed mylonites, where the motion of rocks at interfaces has milled their hard and soft crystalline components into pulp.
As fine division accelerates ion exchange, some clays originate this way, and subglacial grinding sometimes contaminates admixed ice with silicate and clay mineral particles fine enough to dispersion strengthen the frozen bulk, stiffening some layers and rendering interfacial flow complex- basal melting is not the only determinant of ice rheology.
The clear bulk ice is a product of re crystallization, and recrystallization can erase dynamic history much as retrograde metamorphism obscures metas*matism in ‘dry’ rocks.
I’m curious how their findings relate to the isostatic adjustment issue raised by Wu et al. 2010 (doi:10.1038/ngeo938), which led the latter to conclude that mass loss in Greenland and Antarctica was roughly half what other recent GRACE-based studies had found.
While not an expert, it’s safe to say that ice cores drilled for climate study most probably would not be drilled in such areas. The exception might be for surface accumulation studies and then the cores would be relatively shallow. (Accumulation rates are so low that short cores can record centuries of data.) Cores for climate records tend to be drilled in unexciting places — ice divides, slow moving ice, places with little or no liquid precipitation (not a problem in most of Antarctica).
The ice sheet is relatively flat at the surface, with respect to the size of the mountain ranges and their relative topography.
Pressure is a scaler (strictly speaking for liquids), so that along the mountain ridges and integrating downward, the normal forces pretty much cancel thenselves out on either side, resulting in little to no net lateral forces upon the mountain ranges, in total (assuming full contact).
Ice sheets, like water, will seek the path of least resistance. Their flow field will be predominantly perpendicular to the bottom contours/topography, somewhat similar to slowly varying open channel flows of water.
The major heat source at the bottom of an ice sheet is primarilarly from within the Earth itself (thus the submerged lakes seen there, subjected to very high pressures).
I used to be a Research Hydraulic Engineer, in a previous lifetime, with much of my work involving naval architecture of floating and submerged bodies, so, for example, a neutrally buoyant submarine has a zero net force (and moment) acting upon it, the same applies to freely floating bodies.
Having said that, the ice sheet is moving relatively slowly, there are friction forces, separations occur with the bedrock, so that, as one would expect, erosion of the bed will occur, as the ice sheet grinds ever so slowly away on the bedrock.
In closing, mass continuity is preserved at the bottom of an ice sheet, it moves that liquid (under very high pressure) from point A to point B (in this case if the slope is steep, the high pressure water moves upwards, because the ice sheet loses it’s direct contact pressure with the bedrock (also remember rho water > rho ice), the water pressure is greater then the ice sheet contact pressure, then refreezes, the cycle repeats, and you get “ice growth” at the bottom-sides). Nothing gained and nothing lost. Kind of like robbing Peter to pay Paul, if you know what I mean.
Little to no heat is generated from within the ice sheets themselves, they can be heated from the Earth’s interior, or they can be cooled from the Earth’s surface.
Finally, here’s a link to the Rignot paper (I’m still looking/waiting for the Science weekly e-publication of Bell’s paper though, it might better explain the physics than what I have assumed in my explanation above, but I think I’m fairly close to guessing the correct physics, YMMV);
[Response: Other terms will oscillate – thermal expansion, ground water extraction, mountain glacier, irrigation demands etc. Given the uncertainties in those, we’ll only get a credible closure on relatively long decadal timescales. – gavin]
I’m not sure where you get the statement “even in the highest forcing A1F1 scenario, the IPCC calculated only a 0.3 mm/year contribution from the ice sheets averaged over the whole 21st Century”.
From Table 10.7 of the AR4 WG1, it seems we need to add the average contributions for “Greenland Ice Sheet SMB”, “Antarctic Ice Sheet SMB” and “Scaled-up ice sheet discharge”. Over the ~105 years between 1980-1999 and 2090-2099, these contributions are:
I do find this radar penetration technology very interesting, it might help them find places where the fabled 1.2-1.5MYa ice core(s) could exist, that they all all would like to drill for on the EAIS (the one where they pick up the 100KYa to 41KYa transition sequence). Can’t remember that acronym now, but older ice cores (AFAIK) are expected to be near mountain ranges, which are further removed from the Earth’s internal heating (as seen in this paper).
Sea level rise will not be uniform. Some coastal areas will see much large increases than others. But, I have not seen a study that gives estimates of which areas will see higher than average increases and which lower around the globe. Does anyone know of such a study?
Thank you both; EFS_Junior (#18) & Hank Roberts(#23).
Heh – there are conflicts in the two papers you’ve cited. But that’s the best of it, isn’t it?
Bestmann’s(et al) temperature numbers are huge (“…giving flash temperatures of 274 °C (slow speed model) to 239 °C (high speed model).”). And oddly, higher for slower-moving ice. I had to wade through the numbers on that – I thought he’d accidentally reversed a sign or somesuch. And that was 2006 – five years ago. We’ve added so much since then.
In any case, thank you both again – I’ll go back to lurking now…
Comment by Jaime Frontero — 11 Mar 2011 @ 12:51 AM
Sidd, the time scale doesn’t seem to be too short for isostatic adjustment to matter; all these studies correct for it one way or the other, Wu found their correction made a big difference over as short a period as 2002–2008, and Rignot covers two decades.
I’m not sure how to compare Rignot’s and Wu’s results (or whether they are comparable), but by a naive calculation, Rignot too gets more than half the Greenland + Antarctic mass loss rate of Wu.
Since Rignot et al. find good agreement of the GRACE gravity method with the totally independent mass budget method, I reason that their findings disconfirm the novel isostatic adjustment corrections of Wu et al.
But I’m a total layman here, so please clue me in if I’m reading it wrong.
Yep, the papers don’t conflict, they describe different situations; and those are just two out of a large number of papers. This isn’t simple and isn’t all measured, some is theoretical. There are some experts reading here, pointers welcome to papers that would help the rest of us with yet another huge field of science to learn about.
It needs to be remembered that there are significant temperature gradients in the solid ice. Those temperature gradients are the only way the geothermal heat is transported to the surface. In liquid, there can be convection, but the density of water is highest at 4 C (at one atmosphere).
The strength of ice is a very strong (and non-linear) function of temperature, at the melting point it goes to zero.
The higher density of liquid water is the reason that ice sheets always collapse catastrophically. The pressure at a column of water is higher than at the bottom of a column of ice, and at the melting point the ice has essentially zero strength. This is what causes melt water on top to flow to the bottom.
When that water meets ice that is at a temperature below the melting point, the water freezes and deposits its heat of fusion. That warms the ice up to the melting point. Once the whole ice column is at the melting point, there is no temperature gradient for heat to flow down. The ice at the base stays at the melting point where it has very little strength.
My guess would be that there is a high temperature gradient up stream of the melt pocket and a lower temperature gradient down stream. My guess is that what is keeping the system stable is the cold ice being convected into and past the melt pocket faster than the melt water can flow “upstream” (because the cold ice is strong enough to resist the pressure differential of the water vs ice hydrostatic pressures).
At some point, as the temperature of the ice flowing down stream gets higher, it won’t be enough to maintain the ice cold enough to maintain its strength to resist the flow of water. Once the water flow starts, it will warm that ice and weaken it still more and there will be positive feedback until it collapses catastrophically.
As I recall, some of the earlier work on Greenland ice balance and ice sheet stability was done via altitude measurements and indicated that there wasn’t much change.
The GRACE measurements contradicted this and did show a reduction in total ice. My question, is the observation of not much change in the height of the top of the ice while there is a change in the amount of ice present an indication that the density of that ice is going down; in other words that the average temperature of the whole ice column is going up?
Dan H. above points to the recent open access article (full text available):
Climatic Change (2010) 100:733–756 DOI 10.1007/s10584-009-9689-9
(I don’t see any surprises there; it’s a new method proposed and evaluated for getting more detail out of the available proxies; nice graphics).
Persistent multi-decadal Greenland temperature fluctuation through the last millennium, by Takuro Kobashi, Jeffrey P. Severinghaus et al.
Re # 32 I concur strongly, and suggest that the Missoula floods (and similar) were the result of a progressive collapse of a valley full of ice at its melting point rather than the discharge of a melt water lake.
Thus, apparently solid ice can convert to a Jökulhlaup without a volcanic trigger.
> Are you saying that the temperature increase in
> Greenland is expected due to long term fluctuations?
Nonsense. I’m not saying that.
The paper you pointed to isn’t saying that.
A few denial sites are saying that. They’ve been saying “temperature increase … is expected due to long term fluctuations” regardless of the science. That’s a common PR denial talking point.
Read the paper you pointed to.
They describe a new technique that may get better information out of the available proxies and give better information about the natural variability in the past.
Anthropogenic climate change is added on top of the natural variability.
No surprise there.
I read the paper. That is why I brought it up. The results are different from other proxies, not just a diffferent technique. What I am trying to discern is how much of the recent warming in Greenland (and glacier melt) can be attributed to climate change, and how much to natural variability.
About Meteor (#7, #11) and leftymartin (#20) concerns.
If there’s no accelerating trend in sea level rise (cf. Topex-Jason) and if Rignot at al 2011 is correct, we whould conclude that the steric change (from thermal expansion) of SLR is decreasing.
But if so, where is the ‘missing heat’ (Trenberth) or ‘global warming still in the pipeline’ (Hansen) – heat storage in the ocean, whose first effect would be an increasing SLR from thermal expansion ? Does it mean that transient climate response (as expressed by ice sheet or see-ice melting among other events) to GHGs is not so far from equilibrium climate sensitivity ?
Post scriptum : furthermore, RC recently commented the Lyman 2010 paper, finding an increase in ocean heat content 0-700 m from 1993 to 2008, nearly the same period Rignot and Velicogna observe the ice-sheet increasing contribution. These causes should add for SLR, shouldn’t they ? Which if any of the three measurements (ocean heat, ice-sheet, SLR) is considered as the less robust in climate science community?
In light of the enormity of the current clamity in Japan, especially Sendai and the scale of the earthquake 8.9; taken with a whole cluster of similiary sizable and deadly quakes all within the past 3-5 years all over the globe how much study is being done on the correlation between global warming and tectonic activity?.
I have been hearing about large and destructive quakes almost on a monthly basis for a number of years now. To me it’s unusual that the last 10 years have been progressively the hottest on record (both land and sea) and it’s seems to fit with a corresponding increase in significant tectonic instability of the large continental plates and the smaller fault lines that crisscross them almost everywhere on the planet. I’ve asked this question before on this forum and I think Gavin or Eric said as far they were aware there was no connection. Have you looked into this any further perhaps? I’ve still got this annoying feeling in the pit of my stomach that the two are related but don’t know which direction to start.
Any feedback on this will be very welcome.
Comment by Lawrence Coleman — 12 Mar 2011 @ 4:15 AM
Have there been any studies examining if accelerating global ice melt rates have any impact on seismic activity?
With the immense volume of glacial ice being shed each year, we are looking at a tremendous reallocation of weight upon the earth’s surface in an exceptionally short time (by geologic standards). Considering that isostatic rebound occurs even where comparatively small glaciers have receded, is it not plausible that the billions of metric tons of ice melted annually is not only contributing to isostatic rebound, but affecting even the tensioned detente between tectonic plates? And that the consequent readjustments might be reflected as earthquakes?
I have been hearing about large and destructive quakes almost on a monthly basis for a number of years now.
Cell phone cameras and other lightweight, portable still and video devices mean that news agencies have a lot more footage to inundate us with. I suspect you’re noting more coverage rather than more earthquakes. I’m in my 50s and until recently you never got much footage of a post-quake tsunami, for instance. The last two large tsunamis, thailand a few years back and now japan, yielded more video than I remember seeing the rest of my life put together.
Thanks for the answer/link Didactylos. That’s a good point dhogaza regarding modern media saturation. And of course there are more seismographs in the world as well.
Accepting that there is no measured increase in earthquake frequency thus far, is it implausible to consider that at some point, the annual reallocation of billions of metric tons of ice, which has been suppressing the earth’s crust with its weight, would affect plate tectonics?
I am not fishing for catastrophes: there may be a scientific basis for this not to occur. I just wonder if there is a point at which the intensification/recalibration of the carbon cycle and hydrological cycle will correspond with an intensification/recalibration of the tectonic process.
I’m more than happy to agree with Didactylos(#45) and USGS on recent siesmic activity, and Dhogza’s (#46) point about the proliferation of cameras is also obviously correct. The worlds stock of large-scale tsunami footage has been massively boosted in the last decade. Some of the footage from Japan has been quite staggering, and also quite distressing.
Another point to add is that we should surely expect to see an increase in the human cost of earthquakes, tsunamis and vulcanism over time, due to the increase in global population.
Like Lawrence I have also posted questions about possible connections between climate change and seismic/volcanic activity. The response has generally been pretty negative on RC, but I think this is partly because in the trenches of the ‘Climate Wars’, there is little enthusiasm amongst climatologists to open another (somewhat speculative) front.
As far as i can see (and i am merely an interested layman who never even finished my enviromental science degree), amongst geoscientists there is considerably more interest in this link.
Everett(#44) might be interested in the results of a very quick google i did, which turns up this…
This article contains comments from 3 geoscientists who all refer to evidence of this link. All of the comments are actually from 2006, since which further evidence has been published.
When i previously quoted one of these geoscientists, Bill McGuire, in previous questions on RC, regular posters highlighted that McGuires research institute was partially funded by the insurance industry. This rather familiar ‘skeptical’ tactic of impuning a scientists professionalism was rather depressing.
He is the former director of the Benfield Hazard Research Centre at University College London, which is the largest academic hazard centre in Europe, and the author of over 300 books, articles and papers.
So i take pleasure in quoting him again, from the article linked to above…
Bill McGuire, professor of Geophysical Hazards at University College, spelled out the scenario further in a 2006 article in New Scientist, titled “Climate change: Tearing the Earth apart?”.
“It shouldn’t come as a surprise that the loading and unloading of the Earth’s crust by ice or water can trigger seismic and volcanic activity and even landslides. Dumping the weight of a kilometer-thick ice sheet onto a continent or removing a deep column of water from the ocean floor will inevitably affect the stresses and strains on the underlying rock,” he wrote. “[While] not every volcanic eruption and earthquake in the years to come will have a climate-change link… [As] the century progresses we should not be surprised by more geological disasters as a direct and indirect result of dramatic changes to our environment.”
McGuire has written an article about the Japanese disaster, published yesterday…
Of course there is a positive correlation between recent global warming and large earthquakes – but there is also a correlation between earthquakes and the number of reservoirs, the number of obese people, and the number of iPhones. Correlation does not mean causality! All it means is that two things share the same trend, such as a recent rise, whether there is any relationship between them or not.
In this case, if you look closely, McGuire and others are talking about geological events that have some proximity to recent changes in ice loading. That’s not the case for the recent large earthquakes.
Most scientists won’t pursue a putative relationship between global warming and recent large earthquakes because of a lack of a plausible causal mechanism. This means there would be an excellent chance that they’d be wasting valuable time on a wild goose chase.
Scientists have been through this drill many times before, e.g. solar cycles and various posited correlations with weather. This has led to the development of a large body of statistical tests aimed at distinguishing random events from actual relationships.
someone could make a statistical analysis on the clusters of larger earthquakes keeping in mind that quakes under 6.5 may have gone unnoticed as late as 19th century on areas with less population. assuming the processes within the mantle are constant, there should be some clustering present, shouldn’t there?
It seems to me that the more rapid decompression of the crust could be a mechanism that would influence other plate activity. It might not be, or it may be impossible to determine, or the spreading epidemic of obesity may be offsetting the lost glacial ice weight – I don’t know.
I appreciate the skeptical approach that there is no relation until a viable theory is borne out by multiple experiments. Another skeptical approach would be to question the position that two of the largest mechanisms adjusting the earth’s crust have no bearing on each other.
My calculator isn’t big enough, but I’d be curious (and I accept that this may be no more than a party trick factoid) to compare how much earth is moved by isostatic rebound compared to a major earthquake.
[Response: That’s easy: earthquakes can move the crust vertically by cm to m in a few tens of seconds (let’s call that mm/s); isostatic rebound occurs at rates of mm/year (or less). So the difference in magnitude is about a factor of around the number of seconds in a year, or about 30 million.–eric]
Interesting idea Aaron. I’ve ranged all over the mountains in the area of Lake Missoula. How do you explain the visible shorelines, if the valley had been full of ice until the moment of melting? I’m assuming the ice you hypothesize was still in glacial motion at the time of the hypothetical sudden melting, so wouldn’t that have erased the humps on little shoreline humps on numerous mountain slopes? Or maybe what I saw as humps were somehow formed some other way and i’m just confused? (I’m not a geologist)
Thanks for the calculation Eric. Along with upgrading my calculator, I should probably upgrade my cerebellum.
Originally I was pondering a comparison of earthquakes and isostatic rebound over time – curious to know if there was a hare – tortoise relationship where the tortoise might eventually catch up. But considering the magnitude and frequency of earthquakes, especially if we take into account the lower end of the Richter scale from .1- 3.0 magnitude, the tortoise has no chance. That is: plates are always in motion, constantly surpassing isostatic rebound rates.
Thus any relation between isostatic rebound and tectonic activity would be of fantastically miniscule proportions.
All right – I think I have caught up with the rest of the class.
re # 56 Steve,
I think that in cold years, Clark River froze in place and did not move. There would have been shallow pools of water (from the Clark River in the summer) that formed the wave benches. In warm years, moulins would form, and falling melt water from above, would rapidly warm the ice until it suffered a progressive collapse.
We think that lowlands will be warmer than higher altitudes. However, sometimes basins catch draining cold air and are colder than the slopes above them.
Glacial Lake Missoula formed when a tongue of the Cordilleran Ice Sheet blocked the outlet of the Clark River in Idaho. Eventually the water level behind the glacial tongue built up to the point where it washed out the ice releasing the lake waters. This happened at least 25 times over a 2000 year period from 15,000 to 13,000 years ago.. Geologists estimate after each flood it took an average of 55 years before the tongue washed out again.
It was not a result of the Clark River simply freezing solid or ice melting quickly (on a human scale, ice was melting relatively quickly on a geologic scale at the time).
59 and 56. Glacial Lake Missoula was formed by the damming of the Clark Fork River by a lobe of the continental ice sheet in the general vicinity of Sandpoint, Idaho. It was a lake and the shorelines reflect the depth of water in the lake and the wave action on the shorelines at that specific surface water elevation. Like any large lake in the northern tier of states or the Canadian provinces, it may well have been covered with ice during cold winters but neither the lake nor the Clark Fork River ever froze in place.
What I’m hearing (from reading here and elsewhere) is that while the re-arrangement of Earth’s water may have a seismic effect, the effect will be indistinguishable from general low-level seismic activity at the scale we are currently able to measure. It’s background noise.
Comment by One Anonymous Bloke — 13 Mar 2011 @ 3:39 PM
I don´t think the sea level will rise on some places in one time; it may have a different forms. Have you consider also the seabed abnormalities caused by earthquakes? As we know from the latest one there was a huge whirlpool that certainly changed the seabed. And by my opinion it may have an influence on the sea level after the water drops down back again.
Meanwhile, a newly active volcano, Shinmoe dake, in the southern island, Kyushu, may end up cooling off the planet for a couple years if it blows big–but that will not be of much comfort to the already triply besieged citizens of Japan.
To further explain Lake Missoula, it catastrophically emptied about 50 times when the water floated the ice dam. The multiple shorelines were caused by thinner ice producing successively lower lakes. It doesn’t seem to involve pressure melting.
Comment by don gisselbeck — 13 Mar 2011 @ 11:38 PM
Hi as a person with no formal expertise and am just an interested plebe, in item of info I read years ago in response to Lawrence (43) . A hypothesis that was raised and supposedly presented to Einstein who considered it a possibility but had other interests. Namely that warming of the oceans increases atmospheric H2O increasing atmospheric energy, this as with ENSO deposits more snow at the poles and northern winters, but more importantly extreme monsoonal and cyclonic rainfall in the tropical areas on fixed land masses as in Aust recently close to the rotational circumference provides a rotational imbalance due to mass transfer from the fluid oceans to the fixed land mass and slight wobble, being seasonal the Earth does not compensate and it results in a seasonal flexing of the plates . I too would be interested if anything further has been researched in this area. Re insurance connection. Believe me I would trust their research scientists more than many others, the ultimate bookies are only interested in the odds and the facts.
The goodness of a model depends on how well it predicts future behavior of the system. Our models of ice flow are still pretty crude, but most of the uncertainty is on the high side.
As to climate models, they are adequate to have predicted a more than 30 year warming trend, as well as the spatial and temporal characteristics of the warming. Again, though, there is a fair probability that the models underpredict the severity of the problems we will face. Uncertainty is NOT your friend.
This comment follows the embedded thread here related to Glacial Lake Missoula “wave benches” (#56, 59, 62, etc), but also does dance at the edges of this larger discussion about liquid water at the edge of ice, deep valley freezing, etc.
1. There are good reasons to think that the “wave benches” of Glacial Lake Missoula, along the mountain sides in north western Montana-Idaho border country, may not all be due to old shorelines (and maybe none of them are…).
“Cryoturbation steps” are well described in the physics literature about effects of freeze-thaw cycles. My favorite resource is a wonderfully written book by Neil Davis at University of Alaska Fairbanks (UAF) called “Permafrost – A Guide to Frozen Ground in Transition” (still in first edition from 2001 – things change slowly in this field?). He discusses the phenomenon at length, with thermodynamics as his base to the science.
Meanwhile, if you wander around the hillsides in the historic Lake Missoula region, those benches are persistent and very regularly continuous, including areas that just could not have been old lake shore. They are predominantly seen on north facing slopes, which is where cryoturbation effects are most likely seen at lower latitudes. The cryoturbation effects are independent of any body of water, frozen or not…
2. Davis’s book is built around his “Universal System Happiness Rule” that restates the 2nd law of thermodynamics as: “Every system is happiest when it contains the least possible amount of free energy.” He uses that concept to explain all matter of the odd things that happen in regions where permafrost is common, including the presence of super-cooled liquid water molecular skins on surfaces of ice at bottoms of frozen mountain valleys. The ice formations described at the start of this thread are well in range of those explanations.
Spoiler alert: you do need to (re)capture grasp of thermodynamics to follow the arguments, which can be a gatekeeper for many of us whose areas of science don’t require much physics. The book served as nightly sleep aid for me for weeks until I managed to keep awake long enough to put it together…
This thread serves as another example of that problem common to translating science for real world consumption – not so complicated once you grasp the basics, but most of those basics are much more complicated than the common world view… Faith is easier.
Post 70: It seems like this is once again wandering off topic, but this discussion illustrates the classic: It is not necessary to understand something in order to argue about it…
“Meanwhile, if you wander around the hillsides in the historic Lake Missoula region, those benches are persistent and very regularly continuous, including areas that just could not have been old lake shore. They are predominantly seen on north facing slopes, which is where cryoturbation effects are most likely seen at lower latitudes. The cryoturbation effects are independent of any body of water, frozen or not…”
In fact, in western Montana, north slopes, or aspects, are typically timbered and are the least likely place to see any evidence of Glacial Lake Missoula. The shorelines visible on Mt Sentinel immediately east of Missoula are a west facing slope and similar evidence of Glacial Lake Missoula are found on south facing slopes north of Missoula, among other places. Have a look at this photo: http://formontana.net/shores.html and draw your own conclusions.
Since the water depth where Missoula now sits was estimated to be 950 feet deep, why could these areas have not been a lake shore?
So your counter point is a “new assessment of the net mass balance of Antarctica and Greenland.”
What validity would this assessment be if it was at all modeled before this new information was introduced?
Is that your story?
Oh, there is some guys out there that show a whole new hydro-dynamic process regarding ice sheets, but lets not forget this other assessment that may or may not even be relevant.
Way to go Gavin.
[Response: :) – so gravity measurements stop working if ice is formed differently. Curious. – gavin]
I know this thread is about ice sheets and not particularly about sea ice, but still, the developments in the Arctic over the past few years, and especially the sharply declining ice volume numbers as estimated by models like PIOMAS made me realize something very interesting and also very obvious:
I think it was Trenberth who asserted that currently our GHG emissions cause a radiative forcing across the top of atmosphere, essentially reducing our planet’s cooling, by some 1 W/m^2. On most of the planet, that heat flux goes into warming the oceans, causing the planet to warm up, as witnessed by multiple observations.
However, in the Arctic, that heat cannot go anywhere. It’s the coldest spot around, so it cannot offload heat to another place, and it’s ocean is covered with ice so it perpetually at close to 0 C. So the heat can only go into melting sea ice.
The Arctic covered by sea ice is some 1.5 E 13 m^2 in size. With 1 W/m^2 forcing, this means that the Arctic accumulates some 4.7 E 20 Joule of heat per year that has no place to go. That is enough heat to melt some 1400 Gton (km^3) of sea ice, every year.
Incidentally, if we look at the PIOMAS ice volume numbers, we see a reduction of volume of indeed some 1500 km^3 per year. Look at volume numbers per month, as they reduce year after year : http://snipt.org/wnoP
(courtecy of FrankD posted at Neven’s Arctic blog)
So it seems that Arctic sea ice volume reduction is very easily explained by our GHG emissions, and the reduction in radiation from the Arctic that this has caused.
Please tell me where I made a mistake, because if this is correct, then we have less than 3 years to see an ice-free Arctic ocean in summer.
Even worse, it is a-priori unclear when the equilibrium will be restored, since every year the Arctic still accumulates 5E20 Joule more heat.
Sorry if I posted something in the wrong thread. But the importance of the prospect of an ice free Arctic in the very near future, and the attribution of our GHG emissions as a cause of that scenario, made me realize that it’s better to post a simple attribution calculation in the wrong thread than to let this go by unnoticed.
@ #70 I suppose this is again a bit off topic, but I have lived, hiked and ridden in and around Missoula for decades. I contemplate Mt Sentinel on my morning commute. I have never seen the north facing “wave benches” and the formations on the west and south faces make sense only as shore lines. Today the snow outlines a prominent line 600 ft or so up that can be traced across 2 mountains and several miles. http://www.flickr.com/photos/23839726@N00/5533697330/ and http://www.flickr.com/photos/23839726@N00/5533696914/
(Sorry I haven’t figured out the link business yet.) This is another example of settled science being challenged by strange outlying opinion.
But then ask yourself if you could be wrong a second way, even if you’d been right in your first mistaken assumption.
Is there any place near Antarctica that’s colder?
How could you check? Find an instrument:
“The difference between the extreme cold of outer space and what you measure when you point an infrared thermometer at the sky is caused mainly by the water vapor in the atmosphere, which is warmed as it absorbs infrared emitted by the Earth. Water vapor strongly absorbs the infrared radiation emitted by the Earth.”
Oh, and just to tie that one up, compare the Arctic (an ocean surrounded by land) with the Antarctic (a high-elevation, very low-humidity icecap, surrounded by ocean). What difference does it make if the Arctic ice melts? What do you think? Will the Arctic lose less heat to space when the sea is covered with frozen ice, and the air over that is colder and dryer? or when the sea is open water, and the humidity is higher there?
“Humidity in the Arctic
In the Arctic, the prevalent air mass is characterized by low temperatures and low moisture content. The continental air of the subarctic in winter is significantly colder and dryer than arctic marine air. Steam fog which occurs when cold air moves out over a warm water surface, causing moisture to evaporate into the air near the surface, is common in arctic regions. A typical value of relative humidity at the surface is 50 to 60 percent.” http://nsidc.org/arcticmet/factors/humidity.html
I think statistical analysis of earthquake clusters has to overcome some difficuluties. It is well know that any large event changes the stress distribution over a substantial area. This increases the probablity of other earthquakes in the area -and perhaps on adjacent sections of the same fault system for a number of years. So one has to be able to disambiguate this effect from the signal you are looking for.
There are modern (although much smaler) analogs for the lak Missoula emptying. I think Lake George in Alaska undergoes an annual event. Doubtlessly there are other locations in the world with longer breakout periods.
Note that this graph is heading for an abyss (ice free September) no later than 2016.
After we have an ice free September, radiation can increase again, due to water warming up (just like what happened in all other oceans). However, until then it seems that GHG forcing in the Arctic caused a 70% reduction in (September) ice volume and is heading for total elimination before 2016, at least if PIOMAS and Navy ice-thickness measurements is to be trusted.
Rob there is nothing special about the arctic. The forcing of 1 watt/ meter squared is a change to the radiation balance globally averaged. There is no reason a priori that at any particular location the radiative balance must change by the average. Only that globally averaged that is what you would get for a quasi equilibrium state. Just because the arctic is a net sink, doesn’t imply it is a net sink for the change. Only detailed simulations can answer that question.
I appreciate your comments, but the “detailed simulations” have been done over and over again in many different peer-reviewed publications. Most of these simulations are faced with variability of some 10 W/m^2 in the various heat in- and out-flux numbers. Also, many of these simulations are not even valid for ice-free conditions (they assume ice cover).
The changes that we see reflected in PIOMAS ice volume indicate a long-term loss of some 700 km^3 ice loss per year (recently accellerating to 1000 km^3 loss per year), which is equivalent to a 1 W/m^2 ‘forcing’. So long-term observations of PIOMAS easily fall withing the noise of these “detailed simulations”.
Still, if PIOMAS (and the Arctic ice volume numbers in the link I provided) are correct, then we will hit ground-zero (ice free conditions) before 2016, at a rate of 1000 km^3/year deficit. That translates to a forcing deficit of 1 W/m^2 which would only become in equilibrium (after some ocean warming calculations) if we experience 3 C average temperature anomalies over a 2-3 month period during summer. That means ice free conditions for 2-3 months, and sea surface temperature anomalies of 0-6 C over the entire Arctic region.
That is a vastly different Arctic than we currently experience, folks !
> > You point out yourself that the Arctic can cool only to space.
> No, I pointed out that the Arctic _can_ cool to space, after you missed > that part.
Sure, but the Arctic can ONLY cool to space. And when you realize that in summer ice cannot get above 0 C, all heat due to GHG forcing will go to melting sea ice. Which was my point.
> Next, I pointed to Spencer’s explanation that a cooler object can lose
> heat to a warmer object.
I think you misunderstood Spencer. A cooler object can lose IR radiation to a warmer object, but it will not loose heat, since it will always receive more IR radiation from the warmer object than it loses to it.
> Others point out this isn’t just radiation and melting; air and water
> movement transfer a lot of heat.
For sure, air an water move a lot of heat into the Arctic. But my point is that even if you consider that heat flow to remain constant over long periods (decades), the GHG forcing in the Arctic would explain the reduction in ice volume.
> You’re claiming authoritative sources for data:
> > at least if PIOMAS and Navy ice-thickness measurements is to be trusted.
> You’re fitting a simple curve to recent years. The people
> fitting “natural cycles” curves do the same, picking the chunk of time
> they want.
> Look at the previous century; where do your simple curves fall?
I hear you, but PIOMAS is not an appeal to authority. There is a physical explanation for the trend (GHG forcing), and even for the accelleration of the loss of volume (albedo amplification).
> Perhaps you’d be interested in a wager on this? I can suggest some
> people who might like to make a bet with you on your prediction.
Well, that’s a good one.
I normally engage in bets only when I know the probablities of the outcome.
In this case, there is one issue that prevents me from engaging in a bet.
That is the difference in model projections of ice volume in PIOMAS (collapse by 2016) versus projections in IPCC models (summer ice until at least 2050). That difference I do not understand because I do not know the differences between the models. One key paper is Tietsche et al, which uses IPCC models to project recovery when ice gets too thin (or even ice free conditions).
Give me some time to study that paper in detail, and I’ll be back.
Also, it sure will be interesting to see what will happen this summer in the Arctic.
P.S. Are these “people” that you refer to (that would engage in a wager) scientists ? If so, I’m more interested to hear their argument than to bet with them.
> only cool to space
Nope. Look at the ocean circulation; where does the cold bottom water go? What flows in to replace it? Look at the air circulation — same. You know those bursts of cold air in the American midwest in the winter? What replaces that cold air further north?
Are you accepting Neven’s bet where he believes that Arctic sea ice will set a new low within the next 3 years? If so, then I would tend to side with you as we witnessed higher minimums over the past 4 years making 2007 appear unusualy low. I would not take that bet over the longer term though.
Bell has extrapolated his observations forwards to 2050, as have Vermeer & Rahmstorf (2009). These give an ice sheet contribution of about 150mm by then; a mere 39 years away.
Hansen recently commented that an extrapolation from 1mm/yr this decade plus a guestimated doubling time for the rate of 10 years would give 5 metres SLR by about 2095. But he didn’t give a particularly solid basis for his assumption of continued doubling of the rate.
Are any of these authors prepared to put their necks out and give us a prediction for 2100 AD on the same seemingly robust basis as they used for their 2050 prediction?
It is not that I think the minimum extent of sea ice will expand over the next three years, but that we will not break the low of 2007. The minimum extent has already increased 25% since the low in 2007. It appears that 2007 was anomalously low, just like global temperatures were anomalously high in 1998. The trend is lower, but the extrapolated trend lines do not approach 2007 levels in the next three years. I would not be surprised if this year’s minimum was higher than 2009 considering the rather strong La Nina.
Maybe you will get a willing ear at sites like WUWT or CA or from Goddard, but let me assure you that physics and reality are not particularly graceful towards denial, scapegoating and preconceived belief systems.
Besides that, I’ve given you 3 pointers that show that opinions like yours are no longer believed by the market place. So if you are serious about this, then offer a bet, or anonymously make your money on Intrade.
But for all time sake, stop bothering scientists and the rest of us rational thinking people with your fairy tales that all is nice and dandy with the Arctic and that 2011 ice extent may actually top the 2009 minimum.
The time of denial and blaming scientists and empty rethoric is over.
It’s time we face reality as it has been staring us in the face all along.
My question to you, what really matters more than predictions, is what will your own reaction be if this year does present a new minimum? Will you start to doubt your obstinate refusal to consider global warming as a threat? Or will you just shrug your shoulders, say it’s an anomaly, and bet that the ice will recover 150% next year?
Personally, I’m of the opinion that this year’s ice may well shape up to be frighteningly, earth shatteringly low. I won’t make that a prediction because one can never tell. Last year, looking purely at extent, the ice first stayed high late into Spring, then dropped precipitously, and then just when it looked certain to be headed for another record melt it put on the brakes.
The difference that I see this year is that when looking at the actual ice distribution at The Cryosphere Today, and comparing it to previous years, one can see that while the area of 15% (or 30%) ice coverage is roughly the same as in previous years, if a bit low, the extent of ice breakup in the 15% to 80% range this year is substantially more advanced than in all previous years, including 2007. It’s all counted the same when compiling those simple extent graphs, but it’s not actually the same. Really, if one were to look at the image right now without a date on it, being asked to guess what time of year it is in the Arctic, one might say that it looks like mid to late May or even early June.
Of course, things can change rapidly, but my own understanding is that the ice is and has been rotten for some time, that it has been melting from underneath, but that no matter what happens, the results can always be easily disguised by nature, due to the fact that the sun goes south for the winter and the whole thing refreezes, however thinly and superficially, to mask what is really going on.
Will this be the year that this all becomes apparent? It’s much too soon to say, and I’m never in the prediction business. It’s a fun game, but it’s only a game. Right now, however, the data (the graphs, and the images of the ice concentrations) are all pointing to a precipitous melt this year.
But what are you going to say if it does happen? Will it finally be time to wake up and become responsible about things? Will it be time to use your energies and posts into making people more aware of the issue, rather than heaping praise on people like Watts and Nova and Lindzen for the complicity in damaging the future of the human race?
Yes, the current ice extent is below the 2009 values, but it is also above the 2006 values, and 2006 witnessed the 2nd highest minimum in the past decade. On the flip side, 2010 had the 2nd highest maximum, and look what happened in the summer. Only 2003 showed a continuation from winter into summer. Based on the data, I see no reason that this year should exceed the 2007 minimum.
If you refuse to talk rationally with scientists, that is fine with me. But if you continue your whining and insults, maybe you should go elsewhere, as scientists will take you less seriously.
What is your basis for suggesting that this year’s ice will be “frightening, earth-shattering low.” I made my statement that cold northern waters will keep the ice from reaching a new minimum low. Further, low ice maximum was likely a result of the warmer Greenland temperatures. What do Watts and Nova and Lindzen have to do with my posting energy?
I already provided my basis for suggesting this year’s ice could be (not will be, don’t put words into my mouth) very, very low… the ice appears to be breaking up early (as evidenced at Cryosphere Today), even though the area of concentrations above 15% is still reasonably normal and so the pretty graphs all look not-too-bad.
I can’t find your statement in this thread about cold northern waters, and I don’t think your Greenland logic applies (albedo that far north during winter months is going to be a bare minimal factor — although you do get points for the recognition of a positive feedback potentially in action in the system). I also doubt that La Nina has anything to do at all with ice extent (just because cold water is exposed in certain oceans or parts of the oceans doesn’t mean the whole planet suddenly got instantly colder everywhere — that’s not what La Nina does or is).
I honestly don’t think any of that matters. There are far too many unmeasured factors which we don’t understand right now to predict ice extent in any particular year. All that we can accurately do is to measure the trend (seriously down), evaluate qualitative differences (i.e. rotten ice), and wait and see. Although if I were to jump from a skyscraper, I may not do a very good job at all of predicting exactly where I’ll land, but it’s not too hard to predict the eventual end result.
As far as the Watts/Nova/Lindzen comment… it wasn’t actually directed at you specifically, but rather denial-lurkers in general… although I notice you did completely skip and fail to answer my main question, which I placed at both the beginning and end of my post…
Predicting ice extent is a game for the likes of S. Goddard. But if the extent reaches a new minimum in the next three years, will you begin to take global warming seriously, or just blame it on a “bad year” and keep expecting things to just average out, or to blame things on some other convenient phantasmical mechanism like the end of the latest La Nina or any other convenient excuse?
Sorry, I don’t mean to attack you personally, but I’ve grown tired of the repeat offenders showing, over the course of literally years (not necessarily you, again), absolutely no sign of ever opening their “skeptical” minds to the idea that maybe they are wrong, and it’s time to reconsider.
How many years of decline (ice) and increase (temperatures) will it take for you (and others like you, who are reading but not commenting) to reconsider your rather staunch position?
I disagree that the ice is breaking up early. This year does not look all that different from others, 2005 showed a much earlier break up, and 2010 was much later. My La Nina point, combined with a largely negative NAO, indicates that colder waters are being measured in the northern oceans. 2007 reached its record low in the presence of a large amount of Atlantic water entering the Arctic. I do not see that happening this year, but se ice extent is relatively unpredictable on a yearly basis.
I am not sure what your last two paragraphs are all about, nor what you would expect me to say if the sea ice does reach a new minimum.
Kevin – you should point out that folks need to select ‘Anomalies’ to get the full flavour of the problems exhibited on that DMI map. ‘Warmer than climatology’ is putting it mildly.
The anomaly hotspot off Newfoundland / west of Greenland has been in that area for weeks, and it’s very ‘hot’. I have no idea what the effect will be once the ice gets moving, but it gives no cause for optimism. The other ‘feature’ – for want of a better word – of the anomaly maps has been the fleeting and very small guest appearances of any blue areas. There just don’t seem to be any balancing features of other areas being colder than climatology to offset the really large and persistent ‘hot’ areas.
(Coming from a place that has never recorded a temperature below 0C, I find these conversations about ‘warmth’ in the Arctic a bit disconcerting.)
That’s a good tip, Adelady–I forgot the thing defaults to absolute temperatures. As you say, the anomaly scale is more useful (at least for this purpose.
I know what you mean about the relative scales of ‘warmth’–as a kid in Sault Ste. Marie, Ontario, 80 F was very ‘warm’ indeed. So when I first arrived in Athens, Georgia, to find 95 F (September 5th at 7 PM, no less!) it was rather a shock. But one does adjust.
Sphaerica (Bob) stated the question that really comes to mind when reading your responses :
“what will your own reaction be if this year does present a new minimum? Will you start to doubt your obstinate refusal to consider global warming as a threat? Or will you just shrug your shoulders, say it’s an anomaly, and bet that the ice will recover 150% next year?”
You did not answer this question, which seems to indicate that you are in denial about the ice loss trend in the Arctic.
Would you care to correct your silence ?
You also state :
“This year does not look all that different from others”
You mention a few cherry-picked maxima/minuma which supposedly would give some merit to your statement, while completely ignoring that the 95% of other points that you could have picked would have falsified your statement.
And neither did not give any scientific argument that indicate would show any form of slowdown from the accellerating downward trend of sea ice.
So overall, I conclude that you fail to see what most other people realized a long time ago, or you don’t believe what you are saying yourself.
There is always one test to see if somebody is sincere in their opinion :
Put your money where your mouth is.
I currently have a bet offer outstanding at Stoat, for $ 10,000, that ice extent will dip below 3 million km^2 in 2011, 2012 or 2013. This is about 2 to 3 standard-deviations below the average trend (which is already steeply downward), so if you are serious when you say that “This year does not look all that different from others” then you would jump on it in a heartbeat.
If you don’t want to bet, then you should ask yourself why not.
Why, if you don’t want to put your money on it, are you venting opinions that you don’t even believe yourself ?
And remember that nobody but you yourself can make you realize that you may be in denial about what’s really happening out here in the real world.
Dan, if you want to see whether and how much the Arctic ice is changing, Cryosphere Today has one handy feature, apart from the animation and a whole heap of other goodies. When you scroll down you get the option of comparing one day with another.
Last melt season I made a habit of comparing the most recent picture available – usually a day earlier than the latest day in the animation – with the same date 30 years ago, sometimes with 2007. Very sobering.
Just now I’m comparing this year’s date just with last year’s. Downright nasty most of the time. Doing the same thing for 2007 or for 1980 I reserve for days when I’m pretty cheerful or determined. These comparisons do not make for happy viewing.
But there’s no point in covering our eyes or looking away. This is not a film, it’s reality. Look right at it, straighten the shoulders and get on with what’s needed.
First off I do not that kind of money with which to gamble. Secondly, these are opinions of which I firmly believe, and I support with facts.
I do not know where you are getting your numbers, but the recent ice minimum is still over 50% of what it was in the 1980s. At the current rate, sea will remain for at least another 30 years, not to mention that the remaining ice is located further northward, and in even colder waters than that which has declined over the past 30 years. http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.area.arctic.png
I did not cherry-pick anything, as you are obviously trying to do with your ridiculous statement about disappearing sea ice by 2016. No data supports that statement. My choice of years were examples to show that winter sea ice maximum does not necessarily correlated with summer minima.
I am not in denial about anything. I have a real beef with people using short-term data or single incidents to “prove” something. If we break the sea ice minimum this year, it will just be one more data point to establish the long-term trend. I am not “denying” the trend; simply pointing out that the trend over the last 30 years is -80,000 square km / yr. At that rate, it will take more than three years to melt 3 million square km. http://chartsgraphs.wordpress.com/2010/01/01/arctic-sea-ice-extent-trends-with-r/
Your unwillingness to even address the question speaks volumes to the mindset of the denial crowd. It’s not about truth, or facts, or reason. It’s about a total and complete inability to deal with truth, facts and reason. Your mind just shuts down at even the hint of an outcome which is not in line with your predefined and desired conclusions, to the extent that you cannot even answer a hypothetical concerning possible future events.
You can wander into the most complex train of rational thought, as long as it inexorably chugs towards the destination you’ve chosen. Nothing can derail it, not even that fact that the tracks ahead, let alone the destination, could be purely imaginary.
You repeatedly simply could not bring yourself to answer a simple question which is at odds with your hardened world view.
You really should seriously consider what this means.
I have no clue what you are talking about or what you think I believe. I suggest you talk a few minutes to calm down and check out the science surrounding the Arctic. As I have already pointed out, the sea ice is declining at about 80,000 km2/year, even though Rob above does not seem to accept that. Are you denying that also? The trend line is not projected to pass the 2007 low for about 8 years, why do think a single year might? As I seaid earlier, single year values are virtually meaningless in the long run, however they are used by alarmists and deniers to “prove” thier case. You appear to be among them. If the current trend were to continue, it indicates that the sea ice would disappear completely in about 75 years. Are you unable to accept that? Neither of you have shown anything that indicates otherwise, except for what the gamblers believe. Sorry, but I will stick with the science.
#104–“The trend line is not projected to pass the 2007 low for about 8 years, why do think a single year might?”
Again, you’re looking purely at extent. There’s also this thing called volume, remember? The volume data aren’t as good as we’d like–us ‘alarmists’ are really, really eager to get better numbers from Cryosat–but paying due attention to the third dimension is not “unscientific.”
The most detailed attempts to model the Arctic sea ice decline show seasonally ice-free Arctic waters around 2030, IIRC–and the modeling has so far consistently under-predicted the decline. The suggestion that the ice cap has 75 years left is simply unrealistic.
Even so, Dan, the Arctic ice is not declining as fast as your credibility.
…it indicates that the sea ice would disappear completely in about 75 years. Are you unable to accept that?
Why do you keep dodging the question? I proposed a hypothetical, asked what your reaction would be, and you repeatedly keep arguing about the sea ice. I’m not arguing about that. You can make any prediction you want, and so can I. I don’t care about predictions.
The question I asked which you are so studiously avoiding, and which by your silence screams to the world the true character of deniers such as yourself, is:
How would your position on global warming change if, contrary to your own predictions, the summer sea ice minimum in the Arctic continued to fall in the next three years, rather than to show signs of recovery?
It’s a simple question. It has nothing to do with what will happen or is likely to happen. I don’t care about numbers or trends or this or that.
I care about how you, as a person, will behave given a particular scenario.
If, despite all of your logic and protestations to the contrary, sea ice in the Arctic continues to decline, will you re-evaluate your stance on global warming?
Once again, my position would not change. If the sea ice continues to decline at the current rate, there is nothing to change.
If the sea ice minimum were to decline faster than recently observed, then I would rethink my position and conclude that warming is occurring faster than expected. Similarly, if the decline slows significantly, I would conclude the opposite.
I simply look at the most recent data in line with the long term results and ask myself, is their reason to conclude that a change has occurred? Remember, my position is not that sea ice would not continue to fall, but rather that it would not break the 2007 minimum in three years.
Does that satisfactorily answer your question?
“The trend line is not projected to pass the 2007 low for about 8 years, why do think a single year might?”
That has to be the silliest thing I’ve read so far today. Really, it demonstrates a lot about why Dan is struggling with this whole debate.
Okay, Dan. First, the decline is non-linear. Predicting what will happen is difficult. Second, there is considerable variability. Just as 2007 was substantially below the trend, 2011 or 2012 may be also.
Now, you observe that single years are “meaningless” in the long run, in a failed attempt to turn around that argument we keep making to deniers when they lovingly cherry-pick some date they like. But you got it wrong. Single years aren’t meaningless. They are each one data point. And each year that falls substantially below the trend changes the trend. This is what we have observed. September 2007, 2008, 2009 and 2010 were all below the linear trend as computed by NSIDC.
When we see this on the end of a 30 year downwards slope, it really isn’t hard to see the non-linearity. It also isn’t that hard to analyse just how non-linear it is.
> If the current trend were to continue
You don’t even know if the current trend is linear.
As Tamino has taken pains to point out many times, if simply fitting trend lines or curves to past performance were a useful way of anticipating future events, science would be simple–but as changing the physical world changes what happens, it isn’t.
Dan H.: You are getting very tiresome. I’m sure we have been over all this with you before. PIPS is for submarine navigation, so it calculates the thickest ice in a region, not the average. This makes it largely irrelevant for calculating volume.
2009 didn’t fall on the line back in 2009. But that trend line keeps moving. Next year 2009 may be above the line.
You still don’t get why cherry-picking is bad, and why I’m not cherry-picking. You have all the data right there, but rather than look at it, you replace it with a single line! As I said, my claim isn’t based on eyeballing, but by looking at the actual analysis. Moreover, we don’t *expect* the ice loss to be linear.
Okay, enough. Can you please go back to the bore hole now?
…it is not my calculation, but by the University of Colorado…
That’s offensively disingenuous. You’re implying that the NSIDC and U. of Colorado agree with your logic of computing a linear trend based on 31 years of non-linear data, which is patently false. The graph in the post was produced by one D Kelly O’Day, the blogger at the site, as attributed on the graph itself, using NSIDC data. To claim that that is the position of the NSIDC because it made use of their data is absurd.
How about being a little more obvious, or at least clever, in your arguments?
116, Dan H
…how would it impact your view?
Being a logical and open minded person, I’d retreat 100% from my current position and completely rethink things, long, long before the Arctic returned to 1980s levels.
Comment by John E. Pearson — 4 Apr 2011 @ 10:39 AM
Aside for anyone new to the subject, “Eddie” (3 April 2011 1:59 pm) says “7 feet” — that’s one estimate for this century for melting isolated glaciers, not the longterm number. Look where sea level was the last time the polar icecaps weren’t there. Same amount of water in the world. http://en.wikipedia.org/wiki/Current_sea_level_rise but read the history, there are edit wars going on in climate topics most of the time.