My attention was drawn to a Working Paper by Alan Carlin (1) which was basically about how emissions reductions may be a dangerous strategy to avoid climate change. Much of his perceived threat is based on papers by Hansen (2007) and others who propose rapid melting of the Greenland and West Antarctica (henceforth Antarctica) Ice Sheets that causes a sea level rise of 5 m or more.
RAPID MELTING OF THE GREENLAND AND ANTARCTIC ICE SHEETS IS IMPOSSIBLE!
Hansen is a modeller, and his scenario for the collapse of the ice sheets is based on a false model.
Hansen has a model of an ice sheet sliding along an inclined plane, lubricated by meltwater, which is itself increasing because of global warming. The same model is adopted in many copy-cat papers. Christoffersen and Hambrey (2006) and Bamber et al. (2007). are typical papers, a popular article based on the same flawed model appeared in the June 2007 issue of National Geographic, and the idea is present in textbooks such as The Great Ice Age (2000) by R.C.L. Wilson et al.
Hansen’s model, unfortunately, includes neither the main form of the Greenland and Antarctic Ice Sheets, nor an understanding of how glaciers flow. The predicted behaviour of the ice sheets is based on melting and accumulation rates at the present day, and on the concept of an ice sheet sliding down an inclined plane on a base lubricated by meltwater, which is itself increasing because of global warming. The idea of a glacier sliding downhill on a base lubricated by meltwater seemed a good idea when first presented by de Saussure in 1779, but a lot has been learned since then.
It is not enough to think that present climate over a few decades can affect the flow of ice sheets. Ice sheets do not simply grow and melt in response to average global temperature. Anyone with this naïve view would have difficulty in explaining why glaciation has been present in the southern hemisphere for about 30 million years, and in the northern hemisphere for only 3 million years.
To understand what is possible it is necessary to know something about the physics of glacier flow, which explains a few things not accounted for in the Hansen model, including:
Why are ice crystals at the foot of a glacier a thousand times bigger than those in the snow that feeds them?
Why does lake ice deform at lower stress than other ice?
Why do crevasses only reach a limiting depth?
In reality the Greenland and Antarctic ice sheets occupy deep basins, and cannot slide down a plane. Furthermore glacial flow depends on stress (including the important yield stress) as well as temperature, and much of the ice sheets is well below melting point. The accumulation of kilometres of undisturbed ice in cores in Greenland and Antarctica (the same ones that are sometimes used to fuel ideas of global warming) show hundreds of thousands of years of accumulation with no melting or flow. Except around the edges, ice sheets flow at the base, and depend on geothermal heat, not the climate at the surface. It is impossible for the Greenland and Antarctic ice sheets to ‘collapse’.
A glacier budget
In general glaciers grow, flow and melt continuously, with a budget of gains and losses. Snow falls on high ground. It becomes more and more compact with time, air is extruded, and it turns into solid ice. A few bubbles of air might be trapped, and may be used by scientists later to examine the air composition at the time of deposition. More precipitation of snow forms another layer on the top, which goes through the same process, so the ice grows thicker by the addition of new layers at the surface. The existence of such layers, youngest at the top, enables the glacial ice to be studied through time, as in the Vostok cores of Antarctica, a basic source of data on temperature and carbon dioxide over about 400,000 years.
When the ice is thick enough it starts to flow under the force of gravity. A mountain glacier flows mainly downhill, but can flow uphill in places. In an ice sheet the flow is from the depositional high centre towards the edges of the ice sheet. When the ice reaches a lower altitude or lower latitude where temperature is higher it starts to melt and evaporate. (Evaporation and melting together are called ablation, but for simplicity I shall use ‘melting’ from now on).
If growth and melting balance, the glacier appears to be ‘stationary’. If precipitation exceeds melting the glacier grows. If melting exceeds precipitation the glacier recedes.
How glaciers move
Flow is mainly by a process called creep, essentially the movement of atoms from one crystal to another. The first clues to this came from the study of lake ice, which can flow at a stress much below the shear strength of ‘regular’ ice if the stress is applied parallel to the lake surface. This results from the crystal properties of ice. Ice is a hexagonal mineral with glide planes parallel to the base. Lake ice is a sheet of crystals with the c-axes vertical and the glide planes all parallel to the lake surface, so a push parallel to the glide planes deforms the ice readily. Much greater stress is needed to deform ice perpendicular to the glide planes.
Another method of flow is important in ‘regular’ ice. There is constant gain-and-loss of atoms between different crystals in a mass of ice, and in the absence of any stress an individual grain of ice will lose about the same number of atoms that it gains, and so remain unchanged. But if a crystal is stressed it will lose more atoms than it gains and so shrink, while a nearby unstressed grain will gain more than it loses and so grow. In this way there will be preferential growth of those ice crystals which are oriented in such a way that their glide planes are parallel to the stress, and grains in other orientations will tend to disappear. This is observed in glaciers, where it is found that a preferred crystal orientation appears with distance down-valley, and the ice crystals at a glacier snout have a volume about a thousand times greater than that of the first-formed ice crystals at the source of the glacier. These observations cannot be explained by mechanisms that ignore the crystal structure of ice.
The flow of material in a solid crystalline state is known as creep, and there are three laws of creep relevant to the flow of ice:
1. Creep is proportional to temperature.
2. Creep is proportional to stress (essentially proportional to the weight of overlying ice)
3. There is a minimum stress, called the yield stress, below which creep does not operate.
All these laws have significant effects on glacier movement. Alpine glaciers differ significantly from the ice caps of Greenland and Antarctica, and care is needed to transfer knowledge of one kind of glacier to the other. Incidentally, the physics of ice as described here was worked out over 60 years ago, by people such as Perutz (1940)
Creep is proportional to temperature.
The closer the temperature comes to the melting point the greater the creep rate. In experiments at a fixed stress it was found that the creep rate at -1oC is 1000 times greater than at -20oC. In valley glaciers the ice is almost everywhere at the prevailing melting point of ice, because the latent heat of ice is very much greater than its specific heat. Very little heat is required to raise the temperature of an ice block from -1oC to 0oC; it takes about 80 times as much heat to turn the same ice block at 0oC into water at 0oC. Since the temperature does not vary in valley glaciers they are not affected by this first law of creep.
But ice caps are very different. They are cooled to temperatures well below freezing point, which reduces their capacity to flow very greatly. Ice caps can be kilometres thick, and their warmest part is actually the base, where the ice is warmed by the Earth’s heat, and where flow is concentrated. The drilling of the Northern Greenland Ice Core Project (NGRIP) was stopped by relatively high temperatures near the base and new equipment had to be designed to drill the core from 3001 m to 3085 m. It is because ice only flows at the base that great thicknesses of stratified ice can accumulate, as revealed in the ice cores.
Some Greenland cores show no flow at all. This is cold-based ice. A large geomorphology literature describes delicate landforms such as tors and patterned ground in areas that were formerly covered by an ice sheet. The general view is that cold-based ice essentially preserves any pre-existing landforms, and the erosion potential of cold-based ice is zero or minimal. Importantly for ideas of ‘collapse’, the ice is not sliding: it is not moving at all.
Greenland differs from Antarctica in that the ice sheet spills out through gaps in the mountain rim, and the glaciers overlie deep narrow valleys. According to van der Veen et al. (2007) such valleys have higher than usual geothermal gradients, so it might be geothermal heat, rather than global warming, that causes some Greenland glaciers to have higher than usual flow rates. The overspills have some of the characteristics of alpine glaciers, where evidence of glacier recession is more obvious.
Creep is proportional to stress (essentially proportional to the weight of overlying ice)
This means that the thicker the ice the faster the flow, but a great stress is required if the ice is very cold. This is shown by the huge thicknesses of undisturbed ice revealed by the ice cores that are used to work out palaeoclimates. In Antarctica, in the Vostok cores the undisturbed ice that provides the desired information continued to a depth of 3310 m or 414,000 years, but below this the ice starts to be deformed.
There is a minimum stress, the yield stress, below which creep does not operate.
At the surface there is no stress, so the ice does not flow: at a certain depth the weight of ice is sufficient to cause flow, and all the ice below this limit must flow. The threshold boundary between non-flowing ice and flowing ice marks the yield stress level. The upper, brittle ice is a solid being carried along on plastic ice beneath. Since the flow is uneven the solid, brittle ice is broken up by a series of cracks called crevasses. The base of crevasses marks the position of the yield stress and the transition from brittle to plastic ice.
In Antarctic and Greenland ice sheets crevasses occur towards the edges, where the ice is flowing, but not in the areas of accumulation. In the middle of the ice sheets there are no crevasses to transmit meltwater to the base of the ice sheet, even if it were present (which is impossible).
Some results of the laws of glacier flow
These simple rules of creep allow us to understand some observations on glaciers
The speed of valley glaciers has been measured for a long time, and is rather variable. Sometimes a valley will flow several times faster than it did earlier. Suppose we had a period of a thousand years of heavy precipitation. This would cause a thickening of the ice, and more rapid glacial flow. The pulse of more rapid flow would eventually pass down the valley. It is important to understand that the increase in flow rate is not related to present day air temperature, but to increased precipitation long ago.
Melting and climate
On July 21, 1983, the lowest reliably measured temperature ever recorded on Earth was at Vostok with −89.2 °C. The highest recorded temperature at Vostok is -19o C, which occurred in January 1992, and during the month of July 1987 the temperature never rose above -72.2o C. At these temperatures ice cannot flow under the pressures that prevail near the surface. Warming has no effect at such low temperatures: ice will not flow faster at -60oC than at -70o C.
Ice sheets may take many thousands of years to flow from the accumulation area to the melting area. The balance between movement and melting therefore does not relate simply to today’s climate, but to the climate thousands of years ago.
Glaciers and precipitation
Glaciers and ice sheets are in a state of quasi-equilibrium, governed by rates of melting and rates of accumulation. For a glacier to maintain its present size it must have precipitation as snowfall at its source. This leads to a slightly complex relationship with temperature. If the regional climate becomes too dry, there will be no precipitation, so the glacier will diminish. This could happen if the region became cold enough to reduce evaporation from the ocean. If temperatures rise, evaporation is enhanced and so therefore is snowfall. Paradoxically a regional rise of temperature may lead to increased growth of glaciers and ice sheets. Today, for example, the ice sheets of both Antarctica and Greenland are growing by accumulation of snow.
The age of ice sheets
In the Greenland ice sheet several cores have over 3 km of undisturbed ice which go back in time for over 105,000 years, much less than the Antarctic equivalent. The Vostok cores in Antarctica provide data for the past 414,000 years before the ice starts to be deformed. Dome F core reached 3035 m and Dome C core 3309 m, and both date back to 720,000 years. The Epica core in Antarctica goes back to 760,000 years, as does the Guliya core in Tibet. But what is more important than the age is that vast thicknesses of ice are preserved, and they retain complete records of deposition, in spite of the fact that temperatures at times during that period have been warmer than now. They do not fit the model of surface melting, even infrequently. After three quarters of a million years of documented continuous accumulation, how can we believe that right now the world’s ice sheets are collapsing!
The collapse of ice sheets
Some of the present-day claims that ice sheets ‘collapse’ are based on false concepts. Ice sheets do not melt from the surface down – only at the edges. Once the edges are lost, further loss depends on the rate of flow of the ice. The rate of flow of an ice sheet does not depend on the present climate, but on the amount of ice already accumulated, and that will keep it flowing for a very long time. It is possible that any increase in temperature will cause increased snowfall thereby nourishing the growth of the ice sheet, not diminishing it.
The very ice cores that are used to determine climates over the past 400,000 years also show that the ice sheet has grown over that period by accumulation of stratigraphic layers of snow, and has not been deformed or remelted. The mechanism portrayed by Christoffersen and Hambrey (2006), of meltwater lakes on the surface finding their way down through cracks in the ice and lubricating the bottom of the glacier is not compatible with accumulation of undisturbed snow layers. It might conceivably work on valley glaciers, but it tells us nothing of the ‘collapse’ of ice sheets.
The global warming doomsday writers claim the Greenland and Antarctic ice sheets are melting catastrophically, and will cause a sudden rise in sea level of 5 or more metres. This ignores the mechanism of glacier flow which is by creep. Glaciers are not melting from the surface down, nor are they sliding down an inclined plane lubricated by meltwater. The existence of ice over 3 km thick preserving details of past snowfall and atmospheres, used to decipher past temperature and CO2 levels, shows that the ice sheets have accumulated for hundreds of thousands of years without melting. Variations in melting around the edges of ice sheets are no indication that they are collapsing. Indeed ‘collapse’ is impossible.
Appenzeller, T. 2006. The Big Thaw. National Geographic, June 2007. 56-71.
Bamber, J.L., Alley, R.B. and Joughin, I. 2007. Rapid response of modern day ice sheets to external forcing. Earth and Planetary Science Letters, 257, 1-13.
Carlin, A. 2007. NCEE Working Paper #07-07.
Christoffersen, P. & Hambrey, M.J. 2006. Is the Greenland Ice Sheet in a state of collapse? Geology Today, v.22, pp. 98-103.
De Saussure, H-B. 1779-1796. Voyages dans les Alpes.(4 volumes) Manget, Geneva.
Hansen, J. 2007. Scientific reticence and sea level rise. Environmental Research Letters, May 24.
M.F. Perutz. Mechanism of glacier flow. Proc.Phys.Soc., 52, 132-135, 1940.
van der Veen, C.J., Leftwich, T., von Frese, R., Csatho, B.M. & Li, J. 2007. Subglacial topography and geothermal heat flux: Potential interactions with drainage of the Greenland ice sheet, Geophysical Research Letters, v.34, LI2501, doi:10.1029/2007 GL030046.
Copyright 2007, Cliff Ollier – reproduced with permission
Cliff Ollier, School of Earth and Geographical Sciences, The University of Western Australia, Crawley, WA 6009, Australia [firstname.lastname@example.org]
For duck’s sake at least get what Hansen is saying correct.
(1) Greenland and Antarctica ain’t all gonna melt – a total melt is a much bigger number – like 68 metres.
(2) he’s basing his assertions on paleo history more than modelling – i.e it’s happened before
(3) catastrophic collapse is NOT happening right now
(4) yes his position is controversial but at least let’s try lying straight in bed and quote from his words not opinions pulled out of your backsides or right wing scum/spiv op-eds.
http://pubs.giss.nasa.gov/docs/2007/2007_Hansen_etal_2.pdf says in small part:
“The imminent peril is initiation of dynamical and thermodynamical processes
on the West Antarctic and Greenland ice sheets that produce a situation out of
humanity’s control, such that devastating sea-level rise will inevitably occur.
Climate forcing of this century under BAU would dwarf natural forcings of the
past million years, indeed it would probably exceed climate forcing of the middle
Pliocene, when the planet was not more than 2–38C warmer and sea level 25G
10 m higher (Dowsett et al. 1994). The climate sensitivities we have inferred from
palaeoclimate data ensure that a Business as Usual (BAU) GHG emission scenario would produce
global warming of several degrees Celsius this century, with amplification at
Such warming would assuredly activate the albedo-flip trigger mechanism over
large portions of these ice sheets. In combination with warming of the nearby
ocean and atmosphere, the increased surface melt would bring into play multiple
positive feedbacks leading to eventual nonlinear ice sheet disintegration, as
discussed by Hansen (2005). It is difficult to predict time of collapse in such a
nonlinear problem, but we find no evidence of millennial lags between forcing and
ice sheet response in palaeoclimate data. An ice sheet response time of centuries
seems probable, and we cannot rule out large changes on decadal time-scales
once wide-scale surface melt is underway. With GHGs continuing to increase, the
planetary energy imbalance provides ample energy to melt ice corresponding to
several metres of sea level per century (Hansen et al. 2005b).
With this danger in mind, it is appropriate to closely monitor ice sheet
conditions. Area of summer melt on Greenland increased from approximately
450 000 km2 in the first few years after satellite observations began in 1979 to
more than 600 000 km2 in recent years (Steffen et al. 2004). Iceberg discharge
from Greenland increased markedly over the past 15 years. Mass loss increased
from 4–50 km3 yrK1 in 1993–1998 to 57–105 km3 yrK1 in 1999–2004, based on
radar altimeters, with probable losses at the higher ends of those ranges (Thomas
et al. 2006). Recent analyses of satellite gravity field data yield a net annual loss
of 101G16 km3 yrK1 during 2003–2005 (Luthcke et al. 2006).
The gravest threat we foresee starts with surface melt on West Antarctica and
interaction among positive feedbacks leading to catastrophic ice loss. Warming
in West Antarctica in recent decades has been limited by effects of stratospheric
ozone depletion (Shindell & Schmidt 2004). However, climate projections
(Hansen et al. 2006b) find surface warming in West Antarctica and warming of
nearby ocean at depths that may attack buttressing ice shelves. Loss of ice
shelves allows more rapid discharge from ice streams, in turn a lowering and
warming of the ice sheet surface, and increased surface melt. Rising sea level
helps unhinge the ice from pinning points.
Climate change and trace gases 1949
Phil. Trans. R. Soc. A (2007)
West Antarctica seems to be moving into a mode of significant mass loss
(Thomas et al. 2004). Gravity data yielded mass loss of approximately
150 km3 yrK1 in 2002–2005 (Velicogna & Wahr 2006). A warming ocean has
eroded ice shelves by more than 5 m yrK1 over the past decade (Rignot & Jacobs
2002; Shepherd et al. 2004). Satellite QuickSCAT radiometer observations
(Nghiem et al. 2007), initiated in 1999, reveal an increasing area of summer melt
on West Antarctica and an increasing melt season over the period of record.
Attention has focused on Greenland, but the most recent gravity data indicate
comparable mass loss from West Antarctica. We find it implausible that BAU
scenarios, with climate forcing and global warming exceeding those of the
Pliocene, would permit a West Antarctic ice sheet of present size to survive even
for a century.
Our concern that BAU GHG scenarios would cause large sea-level rise this
century (Hansen 2005) differs from estimates of IPCC (2001, 2007), which foresees
little or no contribution to twenty-first century sea-level rise from Greenland and
Antarctica. However, the IPCC analyses and projections do not well account for the
nonlinear physics of wet ice sheet disintegration, ice streams and eroding ice shelves,
nor are they consistent with the palaeoclimate evidence we have presented for the
absence of discernable lag between ice sheet forcing and sea-level rise.” ENDS
Do I believe him – well depends on paleo history, climate sensitivity and past temperatures. At best this blog coiuld only agree on about 30%.
Anyone want to define an area we could agree on to start with or shall we just insult each other (more fun).
Paul – “Copyright 2007, Cliff Ollier – reproduced with permission
Cliff Ollier, School of Earth and Geographical Sciences, The University of Western Australia, Crawley, WA 6009, Australia [email@example.com]”
So Cliff has submitted this paper for peer review? How did it go?
Pirate Pete says
Thanks for that. Good explanation.
I was recently talking with an acquaintance who lives in Greenland about Greenland glacial melting. He says that the reason for increasing flow rates of Greenland glaciers at present is because sea temperature has recently risen by about 3 degrees. This has caused sea ice to melt, and the sea ice acts as a blocking mechanism to glacial flow. Now that the sea ice is gone, the rate of glacial flow has increased.
He also said that this situation does not worry the Inuit indians, because they have seen it before.
Ian Mott says
Luke posts a blurb of all the usual suspects but does not refute a single point made by Cliff Ollier.
The blurb has all the standard sleaze, like mentioning the change in Greenland ice loss from 50km3 to 100km3 but failing to mention the volume of ice deposition and, more importantly, that the 100km3 annual loss is from an ice mass that is more than 2,500,000km3. An annual loss of 0.00004 of 1%.
And like Luke’s vaseline jar that keeps turning up on the Director General’s desk, we have Hansens “albedo tipping point”. A point that can only take place when the 1500m thick ice sheet has actually melted.
But ice sheets don’t melt from above so this mythical tipping point could not possibly work as a trigger for ice sheet collapse because it will only take place AFTER the ice has gone.
But don’t let the facts get in the way, Gollum, there is always “the precious” to play with.
I see the resident putrid little runt is banging on about his favourite topic of onanism again.
Pity the deposition isn’t where the melt is ocurring hey? The old linearist and reductionist at work doing what tax dodging accounts do best socialising losses and capitalising gains. Sort of like hobby farmers.
You don’t have to melt the entire 1500m sheet. Did anyone say this would happen. No.
In any case I note your reluctance to engage on any matter of paleo records of sea level rise. Don’t you denialists normally rant on about it’s all happened before so it will happen again.
And we now seem to have gone from “oh no liquid water could possibly be present – it would freeze” to saying there is. Whole lakes actually.
Next you’ll be saying that there is more than one source of rare plants that aren’t all on your mate’s farm.
All good front bar bulldust with the “boys” isn’t it. Tell us another story then gramps – like the time you met the scandanavian lasses in the Mediterranean. Although on second thoughts how about not.
A WW2 aircraft has been restored, recovered after fifty years from beneath 100 meters of snow and ice in Greenland.
Did it sink?
Louis Hissink says
It was not a paper for scientific peer review but an expert opinion by a geologist about comments made by Hansen.
Dear Mr. Ollier,
With reference to your recent contribution, THE GREENLAND-ANTARCTICA MELTING PROBLEM DOES NOT EXIST, you may be interested in my correponence with James Hansen some years ago.
From: Volz, Dr. Hartwig
Sent: Thursday, March 18, 2004 5:16 PM
To: ‘James Hansen’
Subject: Slippery Slope
Dear Dr. Hansen,
Thank you for sending me your submitted climate change editorial. Your publications are always interesting reading, though I do not always agree.
One remark: “..many years ago I did a lot of “adventure travelling”, also mountain and ice climbing in Greenland. From this time I vaguely remember the following: the sub-ice geomorphology of Greenland is kind of shaped like a saucer. This is the reason why most of the Greenland glacier can not escape by glacier surge, because of the natural sediment and lava barrier. The same is true for Vatnajokull in Iceland, the third largest glacier in the world. So this situation is different from e.g. the situation of the North American ice shield at the end of the last glacial. The top of the Greenland glacier is far too high and too cold to melt. More details you may find by googling e.g. “Greenland sub-ice geomorphology” or asking an expert directly”.
In other words Ender, Hansen has a serious problem with his understanding of the physics of the Greenland Ice Cap.
Have you read Hansen’s paper Horsesink? Of course not. Where does he say it will all melt? Reference pls! Or be a goat.
Louis Hissink says
Luke, or is it Ken Done, (it doesn’t really matter, but I have gotten under your skin, haven’t I, and without one pejorative or ad hominem thrown at your direction.
But I will humour you – he says it will melt at the edges, but melting glaciers do not disgorge millions of tonnes of ice into the sea, they simply fade away backwards up the valleys.
I have no problem with Greenland’s ice burden melting at the edges – for heavens sake, it still hasn’t receded to the MWP times, (and in England they still cannot grow wine grapes in areas that the Romans are reputed to have).
Luke, to paraphrase the memorable statement in David Lean’s film “Lawrence of Arabia”, you are a “silly” little man.
Louis Hissink says
As Hansen has described, the Greenland Ice Cap sits on a saucer shaped depression. Given the catastrophic melting of the ice, as opposed to the assumed slightly less catastrophic isostatic readjustment of the rocks underneath the Greenland Ice cap when the ice “suddenly” melts, the Hansen’s scenario will more likely result in a Green Lake.
Louis Hissink says
And that would be a fresh water lake, or sea, since melting ice in a continetally sized depression would hardly be expected to flow into a surrounding sea.
Or would be it a Greenland Sea?
Dear Louis – so desperate – I now know you haven’t read it as Hansen makes no mention of the word “saucer” in his paper.
Not all of Greenland is in a saucer shaped depression and he’s not saying ALL will melt. There is also the more important Antarctic contribution.
I notice you’ve now moved from “it can’t melt” to having undergone some melt in MWP times. So keep melting 🙂 ROTFL & LMAO
Strange that a geologist like youself would have no idea about past sea level rise and associated global temperatures. After all this is about history as much as the future.
Phil sends hugs.
James Mayeau says
Everytime I see something like this I wonder when and who is going to get this message out. I mean out so that every Joe Blow on the street can say “Sorry Mr. Gore but the ice cap of greenland is sitting in a bowl and it is impossible for it to flow into the ocean.” or “Sorry Mr. Gore but icecaps melt from the bottom due to heat from the Earth’s core, not from surface air temperature.
I want that guy hounded. I want him mainlining Milk of Magnesia for his chronic worry ulser.
I want him to be embarrassed to show his face in public. I want him to retreat from the laughter when ever he pokes his head out of his limo or greenhouse gas belching private jet. I want the school children to pelt the screen with spitwads whenever they show AIT in a classroom.
That’s not too much to ask for, is it?