Moulins, Calving Fronts and Greenland Outlet Glacier Acceleration
Guest Commentary by Mauri Pelto
The net loss in volume and hence sea level contribution of the Greenland Ice Sheet (GIS) has doubled in recent years from 90 to 220 cubic kilometers/year has been noted recently (Rignot and Kanagaratnam, 2007). The main cause of this increase is the acceleration of several large outlet glaciers. There has also been an alarming increase in the number of photographs of meltwater draining into a moulin somewhere on the GIS, often near Swiss Camp (35 km inland from the calving front). The story goes—warmer temperatures, more surface melting, more meltwater draining through moulins to glacier base, lubricating glacier bed, reducing friction, increasing velocity, and finally raising sea level. Examining this issue two years RealClimate suggested this was likely the correct story. A number of recent results suggest that we need to take another look at this story.
The Acceleration:
Jakobshavn Glacier, West Greenland, retreated 30 km from 1850-1964, followed by a stationary front for 35 years. Jakobshavn has the highest mass flux of any glacier draining an estimated 6% of the GIS. The glacier terminus region also had a consistent velocity of 19 meters/day (maximum of 26 m in glacier center), from season to season and year to year, the glacier seemed to be in balance, as I noted in a 1989paper. This is the fastest glacier in the world, no steroids needed. After 1997 it began to accelerate and thin rapidly, reaching an average velocity of 34 m/day in the terminus region. The glacier thinned at a rate of up to 15 m/year and retreated 5 km in six years. Jakobshavn has since slowed to near its pre-1997 speed, the terminus retreat is still occurring, but likewise is.
Helheim Glacier, East Greenland had a stable terminus from the 1970’s-2000. In 2001-2005 the glacier retreated 7 km and accelerated from 20 m/day to 33 m/day, while thinning up to 130 meters in the terminus region. Kangerdlugssuaq Glacier, East Greenland had a stable terminus history from 1960-2002. The glacier velocity was 13 m/day in the 1990’s. In 2004-2005 it accelerated to 36 m/day and thinned by up to 100 m in the lower reach of the glacier. Helheim and Kangerdlugssuaq combined drain 8 % of GIS. Hence, they are more than canaries in the coal mine. In 2006, the velocity of Helheim and Kangerdlugssuaq decreased to near the 2000 level, the terminus of Helheim advanced a bit (Howat et al., 2007).
The first mechanism for explaining the change in velocity is the "Zwally effect", which relies on meltwater reaching the glacier base and reducing the friction through a higher basal water pressure. A moulin is the conduit for the additional meltwater to reach the glacier base. This idea, proposed by Jay Zwally, was observed to be the cause of a brief seasonal acceleration of up to 20 % on the Jakobshavns Glacier in 1998 and 1999 at Swiss Camp (Zwally et al., 2002). The acceleration lasted two-three months and was less than 10% in 1996 and 1997 for example. They offered a conclusion that the “coupling between surface melting and ice-sheet flow provides a mechanism for rapid, large-scale, dynamic responses of ice sheets to climate warming”. The acceleration of the three glaciers had not occurred at the time of this study and they were not concluding or implying that the meltwater increase was the cause of the aforementioned acceleration. However, many others have made this assertion and are investigating (Stearns and Hamilton, 2007). Examination of recent rapid supra-glacial lake drainage documented short term velocity changes due to such events, but they had little significance to the annual flow of the large glaciers outlet glaciers (Das et.al, 2008).
The second mechanism is a "Jakobshavn effect", coined by Terry Hughes, (1986), where a force small imbalance of forces caused by some perturbation can cause a substantial non-linear response. In this case an imbalance of forces at the calving front propagates up-glacier. Thinning causes the glacier to be more buoyant, even becoming afloat at the calving front, and is responsive to tidal changes. The reduced friction due to greater buoyancy allows for an increase in velocity. This is akin to letting off the emergency brake a bit. The reduced resistive force at the calving front is then propagated up glacier via longitudinal extension in what R. Thomas calls a backforce reduction (Thomas, 2003 and 2004). For ice streaming sections of large outlet glaciers (in Antarctica as well) there is always water at the base of the glacier that helps lubricate the flow. This water is, however, generally from basal processes, not surface melting.
If the Zwally effect is the key than since meltwater is a seasonal input, velocity would have a seasonal signal. If the Jakobshavn effect is the key the velocity will propagate up-glacier, the terminus velocity will be impacted by tides, and there will be no seasonal cycle.
On Jakobshavn the acceleration began at the calving front and spread up-glacier 20 km in 1997 and up to 55 km inland by 2003 (Joughin et al., 2004). On Helheim the thinning and velocity propagated up-glacier from the calving front. Each of the glaciers fronts did respond to tidal variations indicating they had become afloat, detached from their bed (Hamilton et al, 2006). This had been the case at Jakobshavn for the last 50 years, but not for Helheim or Kangerdlussuaq. In each case the major outlet glaciers accelerated by at least 50%, much larger than the impact noted due to summer meltwater increase. On Jakobshavn the acceleration was not restricted to the summer, persisting through the winter when surface meltwater is absent.
As a result of the above Luckman et al. ( 2006) concluded:
“The most plausible sequence of events is that the thinning eventually reached a threshold, ungrounded the glacier tongues and subsequently allowed acceleration, retreat and further thinning. It is reasonable to believe that the 1998 Jakobshavn speed-up, also following a long period of stability, was triggered by the same processes of thinning but occurred earlier and after a shorter period of thinning because the tongue was already afloat.”
Examination of the acceleration of other glaciers such as the Petermann Glacier indicate a much smaller acceleration than that observed on three glaciers we have focused, and indeed it is in the summer and of a magnitude that the Zwally effect could explain (Rignot, 2005). Other large outlet glaciers such as the Rinks and Daugaard-Jensen have been stable since 1960 (Stearns et al, 2005). Many other lesser outlet glaciers have accelerated substantially.
That each of the three glaciers has a reduced velocity in 2006 and 2007 despite some exceptional melt conditions in 2007 further suggests that meltwater is not the dominant driver of the acceleration of the main outlet glaciers. Temporarily, there appears to be a force imbalance at the glacier fronts. This will reduce the annual contribution to rising sea level from glacier dynamic changes. The bad news is that the degree of acceleration that can occur via the Jakobshavn effect is greater in these cases than that from the Zwally effect. The Zwally effect is nonetheless real and also implies a direct sea level impact of greater melt.
The Jakobshavn is of particular importance as it has a bed below sea level for at least 80 km inland from the terminus. In this reach there are no significant pinning points, or abrupt changes in slope or width (Clarke and Echelmeyer, 1996) that would help stabilize the glacier during retreat. It is the only outlet glacier of GIS to lack these, and can then (via backforce reductions) tap into the heart of GIS. We know that surface melting is a slow process for raising sea level. but as Greenland’s major outlet glaciers have recently shown, rapid acceleration can quickly deliver large volume of ice to the ocean. The pace of change is not glacial.
Clarke, T.S. & Echelmeyer, K. 1996: Seismic-reflection evidence for a deep subglacial trough beneath Jakobshavns Isbræ, West Greenland. Journal of Glaciology 42(141), 219–232.
Hughes, T. (1986), The Jakobshavn effect. Geophysical Research Letters, 13, 46-48.
Pelto, M.S., Hughes, T.J. & Brecher, H.H. 1989: Equilibrium state of
Jakobshavns Isbræ, West Greenland. Annals of Glaciology 12, 127–131.,
Thomas, R. H. Abdalati W, Frederick E, Krabill WB, Manizade S, Steffen K, (2003) Investigation of surface melting and dynamic thinning on Jakobshavn Isbrae, Greenland. Journal of Glaciology 49, 231-239.
Thomas RH (2004), Force-perturbation analysis of recent thinning and acceleration of Jakobshavn Isbrae, Greenland, Journal of Glaciology 50 (168): 57-66.
18 April 2008 at 1:39 PM
Thanks for the report, I have one question:
you say “The Jakobshavn is of particular importance as it has a bed below sea level for at least 80 km inland from the terminus. In this reach there are no significant pinning points, or abrupt changes in slope or width (Clarke and Echelmeyer, 1996) that would help stabilize the glacier during retreat.”
yet your photo appears to show a widening at the 2006 position. Would you like to comment?
18 April 2008 at 2:12 PM
not a criticism per se … but this motion of glaciers is complex: at once moving in one direction, retreating in the other and thinning - it therefore seems like a constructive idea to make these motions clear at the outset, people can then form a type of cognitive map, and this will (of course) contribute to understanding, retention and so forth
18 April 2008 at 2:18 PM
Ice loss in Greenland seems to be constrained by outlet glacier calving rates. Is there a point where the mountains ringing Greenland open up such that as the calving fronts continue to retreat, they will begin to greatly widen? Essentially uncorking the plugs to the Greenland Ice Sheet? At that point, the Zwally Effect may become more important than the Jacobshavn Effect. I seem to recall that large parts of Greenland are a ring of mountains with a mushy center that is near or below sea level, like an atoll.
18 April 2008 at 3:12 PM
Another relevant analysis is recent work presented at the AGU fall meeting which assessed how much Greenland’s outlet glaciers would need to speed up to get a sea-level contribution on the high side by 2100 or so. Basically all the outlet glaciers would have to get into a highly implausible state of utter overdrive and stay there with no slowdowns for the entire century to have Greenland contribute a meter or two (pretty sure I have that basic sketch right).
As I wrote on Dot Earth in January:
Some scientists assessing the recent acceleration of ice flows propose that the rates of increase can’t be sustained long enough to get a truly disastrous rise in seas by 2100 from a warming Greenland. Tad Pfeffer, of the University of Colorado, and Joel T. Harper of the University of Montana laid out their argument for caution at the American Geophysical Union meeting in San Francisco in December, and quite a few glaciologists seem to agree with them.
I’d love to see Pfeffer or Harper weigh in here. Pfeffer has a nice pdf with his main findings.
18 April 2008 at 3:46 PM
90 to 220 cubic kilometers/year translates into what in terms of increase in sea level?
Is this a net figure for Greenland as a whole or a gross figure for the glaciers under consideration?
[Response: That’s net Greenland I think, and translates to about 0.3 to 0.6 mm/yr (out of a total of ~3-4 mm/yr currently). - gavin]
18 April 2008 at 3:48 PM
Does anyone know how long it took to empty Glacial Lake Agassiz into the Atlantic?
18 April 2008 at 3:54 PM
Glacial Lake “Agassiz”, link to article follows.
http://www.und.nodak.edu/instruct/eng/fkarner/pages/agassiz.htm
18 April 2008 at 4:10 PM
@Bernie. Earth surface = 511 million square km. Sea = 71% = 360 million square km. 90 cubic km = 1/4 of a millionth km = 0.25 mm. 220 cubic km = 0.6 mm. Both per year.
18 April 2008 at 4:50 PM
Our (me, Joel Harper, and Shad O’Neel) work on estimating the outlet glacier velocities required for Greenland to deliver a really big sea level rise (we looked at 2 m or more) has been submitted for review, so I don’t want to go into a lot of details now. However, the idea is simple, and I’ve talked about this much in many presentations this winter: Take the amount of ice you need to get rid of from Greenland to raise sea level 2 m in the next century, reduce it by your best estimate of the amount that would be removed by surface mass balance losses, and try to push the rest out of the aggregate cross-sectional area of Greenland’s marine-based outlet glaciers. You learn 2 things: 1) the outlet flow speed has to be *really* high, and 2) the volume required is so large that even generously inflated surface mass balance losses can’t touch it.
This is a pretty simple calculation, conceptually anyway. The reason it’s valuable is that for all the recent discussion of fast dynamic contributions to sea level rise, no one has looked at the glacier dynamics that would be required to accomplish it. Rough analogies with past conditions (e.g. sea level rise was big 125,000 years ago, and fast 15,000 years ago, so therefore it makes sense that sea level rise should be big and fast now) don’t take into account any constraints imposed by glacier dynamics, and they neglect the fact that we live in a vastly different world glaciogical world than we did 15,000 years ago. In particular, we don’t have the Laurentide Ice Sheet hanging over us any more. The Jakobshavn Glacier is a monster on a human scale, but in terms of getting rid of the Greenland Ice Sheet fast it’s one of a small number of pretty tiny slots. There are no Hudson Straits in Greenland. There is a fairly large fraction of the interior that lies below sea level, but it’s very poorly connected to the ocean via marine based channels.
The bottom line for me is that glacier dynamics is a very important and unresolved issue (and let’s not forget surface mass balance – it hasn’t gone way and it’s not small). I think there’s been a chicken-little effect at work, however, which tends to make us want to embrace potentially impressive processes rather uncritically. As several other posters have mentioned, we still have a lot of work to do. Let’s get the physics right (or as right as we can), and let’s consider all the sources.
One other point: it’s *not* all Greenland and Antarctica. We neglect the other glaciers and ice caps at our peril. Glaciers and ice caps contributed 28% of total sea level rise compared to 14% combined for Greenland and Antarctica for 1993-2003, using IPCC 4th assessment numbers, or GIC 33%/Greenland and Antarctica 20% for 2006 using Meier et al (Science 2007) numbers. The total sea level rise potential from the glaciers and ice caps is tiny, of course, compared to the ice sheets (50, 60, 70 cm – the number is shifting around. Take your pick). But on the century time scale, 50-70 cm of sea level rise is not tiny. One comment I get a lot is that the glaciers and ice caps will run out of ice soon, so why bother to count them? True enough, they might run out of ice – but under what sea level rise conditions do we regard 50-70 cm as loose change, down in the noise level? The other comment I get is that the glaciers and ice caps aren’t subject to the same dynamic effects as Greenland and Antarctica. They’re not? What about the marine-grounded outlet glaciers draining the Russian and Canadian Arctic, Alaska, Patagonia, etc? How vulnerable are they? The fact is we don’t know – we don’t even have a decent inventory assembled of the marine-grounded glaciers in those areas. We need that information, and until we have it and can answer these questions I’m not ready to write off the glaciers and ice caps.
18 April 2008 at 5:06 PM
I interpret the picture as meaning that the Jakobshavn Glacier has become a liquid water river. Is this correct? If so, there would be no more solid ice Jakobshavn effect and the GIS is free to flow as liquid water down Jakobshavn Glacier’s riverbed. But the bulk GIS ice experiences Jakobshavn effect “shoulders” at the ends of the 2006 line so that the bulk ice can’t flow over a broader front? So the GIS is a “caged iceberg” unable to slide whole into the sea because of 50 or so kilometers of mountains holding it in place? I get the imaginary image that GIS is a dangerous monster trying to escape. Is the bottom of the GIS above or below sea level? If below, could a warm ocean current some day flow through Greenland, adding heat? Can you make for us a 3D picture of Greenland?
18 April 2008 at 5:17 PM
You have this net loss, and people tend to talk almost always about the loss side of it: melting, moulins, calving, lubrication, etc.
How about Greenland’s precipitation? Is there any change in the rate of elevation increase in the interior? Also, as the perimeter of the GIS recedes, when, if ever, does rebound become a factor?
[Response: Net loss includes the accumulation in the interior (that’s what makes it ‘net’). Rebound is already a little bit of an issue - but from deglaciation at the LGM, not today. - gavin]
18 April 2008 at 6:30 PM
Re #9 Tad Pfeffer you say:
“The bottom line for me is that glacier dynamics is a very important and unresolved issue (and let’s not forget surface mass balance – it hasn’t gone way and it’s not small). I think there’s been a chicken-little effect at work, however, which tends to make us want to embrace potentially impressive processes rather uncritically.”
As I see it there has been an inverse chicken-little effect at work. To avoid being called “Chicken Little” the scientists have refused to suggest stories if they are scary and they have emphasised any doubts they may have had.
The IPCC AR4 left out ice melt from sea level rise completely, and scientists have been loath to accept that AGW is causing glaciers to melt. Obviously we are not going to have a rapid rise caused by a pro-glacial lake disgorging into the oceans. We have no pro-glacial lake to do that. However, we should consider the scenarios where a disastrous Greenland ice sheet collapse occurs in case that can happen.
There are two positive feedbacks which have not been mentioned. First, as glaciers melt sea level rises and grounding lines retreat speeding the remaining glaciers’ advance into the sea. Second, as the glaciers melt their height reduces bringing a greater proportion of the glacier below the snow line. Sea level rise has a similar but lesser effect. Both of these cause more melting. Both could end with a runaway melt.
But the biggest danger is the one which is obvious and urgent. When the Arctic sea ice goes the increase in water vapour in the Arctic region will accelerate the Greenland melt. Glacier ice melts by contact with water vapour not warm air. The latent heat in moist air is much greater than the sensible heat. Without the Arctic sea ice insulating the air from the water beneath, the increase in water vapour will be dramatic. This is an obvious and real danger. Why is it not being raised?
Cheers, Alastair.
18 April 2008 at 6:54 PM
Speaking of Ice Caps - this just in.
“Only five large ice shelves remain in Arctic Canada, covering less than a tenth of the area than they did a century ago.”
Trent U. report, 4/16/08
http://www.sciencedaily.com/releases/2008/04/080415205350.htm
18 April 2008 at 7:00 PM
I hope it is net since the meltwater amounts to an average rainfall for Greenland of about 2 to 3″ per year. I suspect, but don’t know, that this is a not excessive proportion of the annual precipitation.
18 April 2008 at 7:35 PM
Mauri Pelto said:
What does the last sentence mean? Especially the part after “pre-1997 speed”?
18 April 2008 at 8:42 PM
Pfeffer’s “back-of-the-envelope” calculations are quite compelling (as presented at the Midwest Glaciological Meeting in Burlington, VT last month). Hopefully these calculations will be more widely available soon.
His observation, “One other point: it’s *not* all Greenland and Antarctica. We neglect the other glaciers and ice caps at our peril.” is important. For example, the south dome of Barnes Ice Cap, Baffin Island (the last remnant of the vast Laurentide Ice Sheet) has experienced a rapid lowering in the last two decades. This is an ice cap, the size of Rhode Island, whose melt water flows into Baffin Bay & the Foxe Basin. (http://climatechange.umaine.edu/glaciology/PDFs/2008Geology24013A1.pdf)
The small glaciers (less than 100 sq. km) of Svalbard do seem to be rapidly shrinking yet some of the larger ones are in near steady-state (unpublished thesis data). JCH asks, (#11) “How’s about Greenland precipitation?” Bamber,et al. (GRL V.31, 2004) found that the largest ice cap on Svalbard (Austfonna) was increasing in elevation and correlated the increase to the decline in sea ice which, in turn, provided more open water and, hence, more local precipitation. They do, however, caution that “large perturbations in the mass-balance of other Arctic ice masses may be expected.”
It seems likely that the “small” ice masses of the Arctic archipelagos will, over the next 90 years, contribute more to sea level rise than Greenland. Yet, there is much (as Pfeffer points out) that we do not know about the state of the smaller, non-Greenland, Arctic ice masses.
18 April 2008 at 9:03 PM
Rather than flow speeds (presumably at or near the terminus) I’d rather see the total flux of ice presented. That way corrections for the cross sectional area where the velocity has been measured (averaged?) are corrected for. Of course this isn’t directly observed.
If I assume surface melting of 1M/year over the interior, say 500e3 KM**2 due to warmer climate & darker ice surface (old wet ice versus clean dry snow) that would contribute 1.4mm/year to sea levels. Significant, but several times smaller than the catastrophic rates in the popular (nonscientific) literature.
Looking at your chart of the Jakobshavn, my concern would be that further retreat would lead to a much longer terminus as the confining topography is bypassed. Or is only a small part of the upstream terrain immediately inland of the current terminus is below sea level. A longer terminus could potentially lead to a large net calving rate. Is this a possibility, or does convergent flow mean that the present terminus should be very stable against further retreat?
18 April 2008 at 9:45 PM
10. Edward, here are some 3D pictures for you
http://membrane.com/sidd/greenland.html
18 April 2008 at 10:23 PM
I wanted to ask a question very similar to one already asked by Alastair in #12: Is anyone looking at what the affect on GIS might be of a warm Arctic sea due to albedo effects once the sea ice is gone in the summer?
18 April 2008 at 11:06 PM
Of the last great meltwater effects between 10,000 and 20,000 years ago there was massive sea level rises (5 meters per century) because there was massive ice sheets that stretched out to its continental shelf, before breaking off and scarring the edge of the shelf itself. Today the only place we have massive ice sheets is in the East Antarctic and to a lesser extent the West Antarctic, but now the world is twice as hot. The geography of Greenland is now preventing a rapid collapse of its glaciers ( something i call the Cascade Effect ) even though the Zwally Effect and the Jakobshavn Effect are at work now as they were 10 to 20 thousand years ago. My concerns are with the West and East Antarctic, especially the openings at the Ronnie and the Ross ice shelf’s in the West and the Amery ice shelf in the East Antarctic. Are my concerns founded.
Cheers Simon.
19 April 2008 at 1:07 AM
Tenney, that is THE question at hand, and I’ll bet no one will even touch it.
19 April 2008 at 2:27 AM
AFP and AP and New Scienist news story here:
Lakes on the surface of Greenland’s ice sheet are draining through the kilometre-thick ice and roaring to the bedrock with a flow rate exceeding that of Niagara Falls.
http://environment.newscientist.com/article/dn13729-greenland-ice-lakes-drain-at-speed-of-niagara-falls.html?DCMP=ILC-hmts&nsref=news5_head_dn13729
19 April 2008 at 6:36 AM
in reply to Thomas: “Rather than flow speeds (presumably at or near the terminus) I’d rather see the total flux of ice presented. That way corrections for the cross sectional area where the velocity has been measured (averaged?) are corrected for”
You’ll have to wait for the paper to come out, but this is how we did the analysis I described above.
19 April 2008 at 7:18 AM
I wonder once the front has retreated from salt water and sea mist that ultracold deep ice could refreeze fresh water and slow the breakup. Notice if you tip dry looking frozen peas into a pot of water that they knit into a frozen block, albeit temporary.
19 April 2008 at 8:01 AM
Re: #12
Although increasing latent heat has been raised before *,
the rapid opening of the Arctic Sea and latent heat effects on Greenland ice warrants immediate attention.
* comment #135 at:
http://www.realclimate.org/index.php/archives/2006/03/greenland-ice-and-other-glaciers/
19 April 2008 at 8:25 AM
As so much of the GIS is grounded below sea-level, it seems to me that the key to any possible catastrophic mass loss is the Jacobshavn effect: the ungrounding of the marine front as the ice thins and becomes buoyant. It seems to me that this has potential for really dramatic sudden mass loss (”sudden” as in hours/days, not decades), because there’s no guarantee of monotonicity in the (hmm, search for a term) hypothetical net areal buoyancy of the grounded ice.
That is, when a marine front becomes buoyant enough to unground, the section of ice behind the marine front becomes the new front. Until that moment, the buoyancy of that section (i.e. whether or not it has enough ice mass above sea level to remain grounded if exposed to the sea) has been irrelevant. There may be areas which already would float if they could, and which therefore will float very rapidly when the grounding line reaches them.
I’m glad this effect has a name, by the way. I’ve been trying to describe it in blog comments for months now, rather ineffectively.
So what we need is detailed topo maps of the bed and thickness of the GIS, and to work out a map of the “net buoyancy”, or some such (i.e. total ice area density subtracted from the area density of a hypothetical column of water resting on the bed and extending up to sea level). This will show the potential for catastrophic loss of this sort.
Oh, and the same thing for WAIS. I gather there is NSIDC data which makes producing such maps a SMOP.
I’m very much looking forward to seeing the paper to which Tad Pfeffer refers.
19 April 2008 at 8:38 AM
I would like to echo Mr. Edmonds inquiry as to the stability of the Pine Island and Thwaites glaciers which seem to connect directly to the Byrd Subpolar Basin, where the ice sheets are grounded far below sea level. I understand that acceleration of the Pine Island glacier has been observed, and there seem to be no natural pinning points. Coupled with the observations of surface melt from
Antarctica, would someone care to comment on the mechanics of glaciers in these sectors ? I seem also to remember a comment by Bindschadler stating that while GIS glaciers could retreat inland from warming oceans, there could be no similar escape for Antatctica.
19 April 2008 at 8:38 AM
Unable to find a publisher for it, I put my saturation article on the web:
Saturation
Readers will see my debt to RealClimate articles which touched on this.
19 April 2008 at 8:48 AM
I’m not a scientist, just a very interested citizen, but may I suggest another “chicken little scenario”:
With the outlets currently limited in size and location effectively damning the flow, might there be a subsequent built-up of melt with accompanying positive feedbacks further inland - supporting a much greater rate of melt than what we see flowing out? Could this be a building gigantic reservoir? Could such a reservoir break-through at some point of “non-linearity” such as when the Mediterranean flowed back into the Black Sea, raising sea levels dramatically practically overnight?
Possible?
19 April 2008 at 9:46 AM
Re: #19 and #21
Dear d.beck,
Have you noticed that water vapour is pouring out of the cracks in the Arctic sea ice in stupendous quantities?
19 April 2008 at 9:53 AM
Could the rapid melting of the ice also trigger mega-tsunamis? Ice can act as cement, stabilizing soil. After the ice is gone, you could perhaps have mountains that can break up and fall into the sea.
19 April 2008 at 10:03 AM
Thank you Mauri Pelto and also Tad Pfeffer for your insightful explanations and comments. It is always good to get some good news even if it is slight.
Those interested in some more information about this topic might be interested in the article in this week’s Nature (available at least at this time without a subscription):
http://www.nature.com/news/2008/080416/full/452798a.html
19 April 2008 at 10:34 AM
Count Iblis: There may be links between tsunamis and deglaciation (Storegga slide is touted) and there is a well-know paraglacial response of rock slopes to deglaciation. But any likely tsunami will probably be rather localised.
19 April 2008 at 1:08 PM
Tad Pfeffer (9) — I doubt that there are any (significant) marine grounded glaciers in Alaska or as part of the Southern Patagonian ice cap. Even Hubbard Glacier
http://pubs.usgs.gov/fs/fs-001-03/
appears to terminate in quite shallow water.
19 April 2008 at 2:30 PM
Barton Paul Levenson (#28) wrote:
Thank you!
It’s a good essay — and I have bookmarked it for future reference…
19 April 2008 at 3:17 PM
Tad Pfeffer:#9: “…Greenland to deliver a really big sea level rise (we looked at 2 m or more)…”
Why choose this particular (unquestionably catastrophic) situation? IMHO this would relate to an overall sea level rise of about 5 meters within 100 years, West Antarctic and higher latitude glaciers included. I never see such a potential rise discussed seriously.
This approach is of course interesting as it might provide an upper boundary for the risk - something that is badly missing. So why not re-compute the situation based on a 0.7 meter contribution from the GIS? That is bad enough for most practical purposes.
19 April 2008 at 4:55 PM
Re No. 34, There are a number of tidewater-calving glaciers on the west coast of the South Patagonian Icefield. The only similar glacier on the Northern Icefield, is the San Rafael (which used to have a high calving flux and velocity until it started receding into shallow water).
19 April 2008 at 6:28 PM
san quintin (37) — Thank you for the information. The issue, as I take it, is whether or not the glacier has dug a fairly deep submarine canyon, one which the terminus still occupies.
19 April 2008 at 7:05 PM
Thanks for a great post. From my perspective the interesting item you raise with both the Zwally and Jakobshavn effects is the persistent increase in the volume of water moving under, over and through these glaciers.
Obviously in the short term the ZnJ effects will give rise to variations in the rate of movement of the glacier, but it is the longer term effects relating to energy transfer that worry me.
Alastair notes that increased water vapour will carry more energy to the surface of the glaciers, likewise these increased water flows over, through and under the glaciers is also transferring vast amounts of energy into the ice. And turbulent flow is WORK being done on the water which generates more heat which is likewise dissipated into the ice.
Do you know of any investigations of current deep ice temperatures of the glaciers and ice caps? I understand that global surface temperatures are not responding as rapidly as they should be when the atmospheric models are considered. Is this ice the sink that is absorbing the currently ‘missing’ global temperature rise?
Among the ice sheet dynamics to fret about I see this change in the temperature of the ice from say -30C to ice-at-0C and the subsequent uptake of the heat to go from ice-at-0C to water-at-0C as the ‘dark matter’ of the cryosphere.
For me this raises the potential of items like the Jakobshaven changing from a ‘cork in the bottle’ of the GIS to being a warm run of open water sloshing about 80km into the GIS, and rather than the cross section available for movement of ice/water being confined to the cross section of the glacier it will increase to the side face area – which is much greater and exposes that new face to the same ZnJ effects..
So if as Arc says the ocean is 360 million sq km, then 2m rise is 720,000 cubic kilometres in a hundred years.
Roughly Greenland has a perimeter of 6600km
Say 10% of this is open to the present-day ocean, gives a ‘gap’ 660km wide for GIS to empty though.
720,000 cukm per hundred years = 19.7 cukm per day = 228,300 cubic metres per second.
228,300 cubic metres per second thru a 660km wide gap = about 350 litres per second per metre of gap.
(Check the numbers, please!)
A sheet flow 350mm deep moving at a leisurely one metre per second. Hydraulically that is VERY possible.
Interestingly the Amazon River - which gets up to 45km wide during the rainy season - discharges at an average rate of 218,000 cubic metres per second. That flow (if not balanced by the water cycle) gives (wait for it!) 1.9m sea rise over 100 years.
http://en.wikipedia.org/wiki/Amazon_River
So 2m in a century from GIS plus other glaciers plus Antarctic is trivial – hydraulically at least.
And of course as soon as the melt starts the ‘gap’ runs up the Jakobshavn and its cousins and for every km back it runs the gap increases by 2km.
And of course the existing wet surface area of the Greenland ice is in fact evidenced by the wetted perimeter others have spoken about – the water on top of, beside, inside, through beneath and abutting the glaciers and ice sheet. It is huge – far more than a mere 660sq km. And its warmer than the ice.
And theres no need to confine this consideration to Greenland:-
Ditto all the above with Antarctica, of course, with bells on…
http://www.abc.net.au/news/stories/2008/04/18/2221062.htm
Oh dear..!
19 April 2008 at 7:19 PM
Replying to David Benson #34: in Alaska, Columbia Glacier has retreated ~16 km up a marine-grounded fjord since ca. 1982, and has ~14 km left to retreat before its bed rises out of sea level. The glacier’s calving flux has *averaged* 4 cubic kilometers/year since the onset of retreat with a maximum of 7 kilometers/year in the early 2000s. Hubbard does indeed terminate in shallow water at present (as is presently advancing), but the terminus is on a moraine; upstream from the terminus there is a long marine-grounded reach, although details are lacking… there has been some airborne radio-echo sounding done there recently with more planned. We should know more about Hubbard before long.
19 April 2008 at 7:22 PM
Replying to Pekka Kostamo #36: Your questions are good ones, and we address these in the paper. I need to wait for the paper to pass through the review process, though, and not leak out its contents in little bits!
19 April 2008 at 8:25 PM
Re 18. Thanks mg for the link to the 3D pictures.
It looks like the Jacobshavn will be getting much wider soon. Is that correct? How much could that affect the need for extreme glacial acceleration to raise sea levels by a meter?
Is there a good breakdown of how much ice is where on the globe and then projections on how much melting might be expected for a given area of ice?
In complete jest:
Why don’t we create a giant damn across the outlet of the Jakobshavn Glacier. It would only be 1 1/2 times bigger than the Three Gorges Damn. This will not only hold back some of the water but could also be used to generate electricity. The electricity could be used to create hydrogen that would be shipped to the US to power all those hydrogen cars that we don’t have the hydrogen for.
19 April 2008 at 10:53 PM
No worries mate. Pat Michaels has the floor. http://online.wsj.com/article/SB120847988943824973.html?mod=opinion_main_commentaries
Disko Bay, Greenland: Temperatures on the island are no warmer than they were in the mid-20th century.
As long as this is what makes it into the press, the truth won’t matter. Write a response. Anyone?
20 April 2008 at 1:07 AM
Eric (#42). I’d surely prefer a giant dam over a giant damn.
20 April 2008 at 1:19 AM
To what extent might long term response to changes hundreds of years ago during the Little Ice Age (LIA) result in glacier surging on the Greenland Ice Sheet and the West Antarctic Ice sheet streams surging into the Ross Sea? More specifically, can one define the response time of a particular ice sheet? Are we seeing the results of AGW in the last 100 years or a change over the last 200 or 500 years?
In addition, this same question could be asked about the valley glaciers in Alaska and elsewhere. How much early 20th century surging and flow could be attributed to LIA addition of mass? And is the current large scale ablation seen on these glaciers due to these glaciers coming to some equilibrium with a warmer world due to coming out of the LIA and response times associated with the large masses involved?
Re 12: The reduced ice mass over the Arctic Sea and increased water vapor as an agent for melting makes sense. But also keep in mind that Lambeck et al (2002) have suggested that loss of permanent ice over the Arctic Sea at the end of the last interglacial allowed for increased accumulation of snow and ice at high latitudes because of the increased amount of moisture available. This seems like a lucid argument for another possible complex feedback in the climate system. See: Lambeck et al (2002). “Links between climate and sea levels for the past three million years.” Nature 419: 199-206
20 April 2008 at 3:53 AM
As I have reacted to the speed increase of the Ilulisat/Jakobshavn glacier in the past, herewith some more comments:
- There is a discrepancy between the above map showing the retreat of the ice breakup points and the NASA map over 150 years (7 MB .tiff file, smaller .jpg file here).
According to the NASA map, the retreat of the calving front in the period 1929-1953 (24 years) was as large as the retreat in the period 1953-2003 (50 years). According to the map at the top of this article, the recent retreat was much faster.
I suppose that may have to do with in-between advancing of the glacier’s calving front?
- The previous speedup in the period 1930-1950 might have been caused by (summer) temperatures which were as high or even higher than in the current period. See the around Greenland (coastal) temperatures up to 2005 here
- Greenland (summer) temperatures seems to be more influenced by AMO/NAO than by the general global warming trend.
- Interesting that the retreat speed in the past few years is decreasing. This is quite unexpected, as the resistance of the downstream ice is reducing, thus one should see an increase in retreat speed…
20 April 2008 at 3:55 AM
42 Eric, data on the volume of ice and potential sea level rise (pslr) associated with the various components are given in a table on this page:
http://pubs.usgs.gov/fs/fs2-00/
East Antarctic ice sheet vol=26,039,200 km3 pslr=64.80m
West Antarctic ice sheet vol=3,262,000 km3 pslr=8.06m
Antarctic Peninsula vol=227,100 km3 pslr=0.46m
Greenland vol=2,620,000 km3 pslr=6.55m
All other ice caps, ice fields and valley glaciers vol=180,000 pslr=0.45
Total vol=32,328,300 km3 pslr=80.32m
20 April 2008 at 4:05 AM
Re #42,
Eric,
You can forget to build a dam at the end of the Ilulisat/Jacobshavn glacier. The water there is about 7 km wide and 700 m deep (therefore the icebergs have a height of about 100 m above the water line!). The fjord ends with an underwater morene, where the (about 800 m thick) icebergs are pushed over by tides, wind and the presuure of the icebergs behind them.
As the glacier/icefjord icebergs advance with a speed of over 30 m/day, any dam (how heavy it may be made) will be pushed away by the forces behind the ice front… Not to be forgotten the harsh winter freezing there…
20 April 2008 at 4:27 AM
Figure 4 on this page
http://nsidc.org/news/press/2007_seaiceminimum/20070810_index.html
gives some very interesting sea ice visualisations from the 1982 to 2007. Around 2002 the sea ice dynamics shows some interesting changes, with what appear to be orthogonal shock waves across the ice pumping cycles. It is interesting to note that it was around this time the Larsen ice shelf broke off. Does the oceanic system with its circulatory reconfigurations strongly couple ice dynamics at the two poles? Do these involve other interesting features (eg formation of large oceanic scale mills) around the antarctic circulatory system (can’t find the link I had, but will post when found)? Thus, could ice discharge at Greenland destabilise ice in Antarctica? [Apologies for the amateur questions].
20 April 2008 at 4:49 AM
OFF TOPIC:
http://www.sepp.org/publications/NIPCC-Feb%2020.pdf
This article was from another article posted by the Daily Telegraph today about the NIPCC (Non IPCC). The names make familiar reading and so does the rhetoric really.
http://www.telegraph.co.uk/opinion/main.jhtml?xml=/opinion/2008/04/20/do2002.xml
Maybe someone would like to reply to them but I guess scientifically the debate ended some time ago but getting political and economic action on climate change still requires a response from those who continue to befuddle the public.
20 April 2008 at 5:21 AM
Why this need to guess about sub-ice water pressures? Technology to measure pore water pressures at kilometre depths is highly developed - oil & gas drilling, mining, even civil geotechnics. Grout in some fibre-optic piezos and measure it.
20 April 2008 at 5:29 AM
An example link for my earlier post concerning large-scale oceanic mills is
http://www.marine.csiro.au/remotesensing/oceancurrents/SE/20070223.html
20 April 2008 at 6:08 AM
Thank you, Tim.
-BPL
20 April 2008 at 6:33 AM
Looking at Google Maps in conjunction with the map in this post, it appears that the Jacobshavn ice front is now inland of the mountains that ring the GIS. Wild.
20 April 2008 at 9:28 AM
replying to GlenFergus #51: Drilled access to the bed and direct measurements of subglacier water pressure have been made many times over the years (for a recent example see Harper et al, Geophysical Research Letters, Vol 34, L12503, 2007). Logistically and technically, however, making these measurements on fast-moving, highly crevassed glaciers is infeasible. (It has been done a few times; for an example see Meier et al, Journal of Geophysical Research, 99(B8), 15,219-15,229, 1994).
Doing such measurements at a place like Jakobshavn would be a tough task to say the least. Having an Oil & Gas industry budget might help, but even then I would have my doubts about success…
20 April 2008 at 9:39 AM
I have a map of Greenland’s basal topography. Interesting, the centre is below sea level - almost certainly depressed due to the weight of ice. The east coast/south coast have relatively high mountains which act as a curtain/retaining wall - hence glacial flow via narrow channels. By contrast parts of the west cost seem to have no curtain wall of mountains. A possible scenario is that this area, not “narrow valleys” would see substantial ice loss. Anyway, just a scenario - has anybody else seen the basal maps - worth looking at.
20 April 2008 at 10:12 AM
54..Nick Barnes, dont forget that google earth or maps are definately not up to date and can be 3-5years old so further retreat will have happened since then. On the subject of calving glaciers and the subsequent added freshwater being released into the sea, already there is clear evidence and measurable decrease in the salinity of the deep waters of the north atlantic current just east of canada. That coupled to a 0.7degC increase in the deep water current in just 1 year. This implies that a slowdown of the current is imminent as occured 20k yrs ago. Only this time the global level of CO2 is considerably higher than it was 20ky ago most likely resulting in a greatly prolonged ice-age, much longer than in the past. Does any contributer to RC know what effect an ice-age in the northern hemi will have on the southern hemisphere ? As the NA current moves futher south and/or stops. I also read that the jet stream winds at around 30-40k ft have changed direction and they are now much nearer the poles than previously- this could well cause much bigger and more destructive tornadoes and hurricanes as they wont get their heads chopped off by the high velocity jet streams and can grow to any size the want..within natural limits of course.
20 April 2008 at 10:34 AM
So given a worst case scenario — 6C increase by 2100 or 2150 — how long would it take for all ice to melt in Greenland? 200 years, 300 years, longer? Under a worst case.
20 April 2008 at 10:37 AM
To Tenney, someone did actually respond to your very valid question about “what the affect on GIS might be of a warm Arctic sea due to albedo effects once the sea ice is gone in the summer?.”
(#25 Pat N. said:
Although increasing latent heat has been raised before *,
the rapid opening of the Arctic Sea and latent heat effects on Greenland ice warrants immediate attention.
* comment #135 at:
http://www.realclimate.org/index.php/archives/2006/03/greenland-ice-and-other-glaciers/
What Pat points to, I believe, is this statement from the article (2006):
“Looking forward, the current (small) imbalance (whether positive or negative) of the Greenland ice sheet is not terribly important. What matters is if the melting were to increase significantly.”
The Arctic Ice Sheet gone in the summer absolutely means an increase in GIS melting. I doubt that even Singer would dispute that (without a large accompanying check).
Pat is one of the United States’ few heroes. He was fired from the National Weather Service for telling a bit too much of the truth.
As to ‘water vapor from the cracks in the Arctic’……uh,…..well….no….uh… .Haven’t been there in a while…….alright, actually never been.
What are you talking about, anyway?
20 April 2008 at 11:35 AM
#43 Mark, I equally can write such dribble, although
I would make it less opaque and easier to understand. I can take any location on Earth, show a surprising cooling effect, and point out that Moulins are for Don Quixote and Sancho Panza….. I could write this way,
but I wont. Because there is more to life than just being paid to be a Don Quixote… There are actually real events, far more interesting… The surface temperature record is vulnerable to attack, with cut and run pot shots, any record is vulnerable to ridicule, as long as no one else is there to respond to the criticism. But what WSJ Quixote’s consistently forget to write about is the disappearance of the perennial ancient Glaciers found all over the world, and especially multi year ice of the Arctic Ocean, true metrics against their arrogant assault on reality……
20 April 2008 at 1:25 PM
Tad Pfeffer (40) — Thank you for the information.
20 April 2008 at 2:38 PM
Global sea level rise is currently at 2.4-3.8 mm/yr (since 1993, IPCC 2007). Assuming that rate stays steady (highly unlikely), you’d get a lower bound of 24-38 cm of sea level rise by 2100.
Now, the 2007 IPCC estimate:
It seems their lower bounds are kind of implausible… and we already know that the AOGCMs missed some important features of the Arctic climate system, the sea ice response at least (IPCC 2007):
The take home point for reporters is that the IPCC has underestimated these trends and their projections are also “very likely” to be underestimates.
Another issue has to do with the rate that the rest of the cryosphere, the mountain glaciers and icecaps, will melt at. The causes of sea level rise are the expansion of ocean water caused by warmer ocean temperatures, melting of the Greenland Ice Sheet and the Antarctic Ice Sheet, and the glaciers.
If we look at Science 16 March 2007, Recent Sea-Level Contributions of the Antarctic and Greenland Ice Sheets, Shepherd & Wingham, we find that:
For the fraction due to thermal expansion of ocean water, see Thermosteric sea level rise, 1955–2003, J. I. Antonov, S. Levitus, and T. P. Boyer, GRL 2005
If so, then the total sea level rise, 3.0 mm/yr, equals 0.40 mm/yr + 0.35 mm/yr + X
Where X is the amount of water entering the oceans from melting glaciers and small icecaps. This number is probably of greater immediate practical importance to human populations. Is it safe to say that the current contribution is then ~2.3 mm/yr?
To quote Tad Pfeffer, #9:
For a nice photo of this, see: River of melting water springing from Nigardsbreen, Norway
Thus, by the time contributions from Greenland and Antarctic sea ice melt become dominant, will all the world’s mountain glaciers and icecaps be almost gone? If so, then there will be a huge water crisis, because many highly populated regions rely entirely on glacial melt for some period of the year for their water supplies. Where will they go? To the coasts, which will eventually be inundated, whether in 100 years or 200 years?
20 April 2008 at 4:13 PM
RE: #60
And they won’t Wayne, that’s the problem. They moderate responses too. Only friendly facts allowed. That’s the definition of propaganda.
20 April 2008 at 5:25 PM
The International Earth Rotation and Reference Systems Service (IERS) suggest an ongoing transfer of mass to the pole(s) since 1998. Does this present a problem for AGW?
http://icecap.us/images/uploads/The_Ice_Caps_are_Growing.pdf
[Response: That’s funny. It’s rare that such a specific conclusion is drawn from the flimsiest of evidence despite direct observations contradicting it (google GRACE). Unfortunately, the adding of leap seconds is not as objective as you might think - (see here), and the complete lack of alternate hypotheses underlines the agenda of the writer. Any water shifts - whether they are towards higher precipitation in higher latitudes, or sea level changes due to circulation or thermal expansion (which is not uniform) etc would seem to me to be candidates for the explanation (even if one were needed). Additionally, it’s not obvious that solar or planetary tidal effects couldn’t be playing a role. And of course, the amount of mass concerned would need to be quantified. Meanwhile there is plenty of evidence indicating that the length of day responds to climate changes (especially ENSO) etc….. - gavin]
20 April 2008 at 7:14 PM
Mark & Wayne (#43 & 60), I figured it out — no warming trend bec they were sticking their thermometers in the ice, so it has been remaining fairly steady, around 32F.
My bigger problem with the article was:
I could tell my CF lightbulb joke again….Nah.
20 April 2008 at 7:39 PM
I’m a bit confused by the post. I understand the “Zwally effect” would be enhanced by warming. But it also seems the “Jakobshavn effect” is at least partly enhanced by warming — warming that thins the glacier and makes it more bouyant. And perhaps by way of increased ocean pertubations at the calving front?? Is there an increase in that type of perturbation due to global warming? Then sea rise would also increase that perturbation and bouyancy (but sea rise is very slow).
Also I read somewhere that reduction of the ice load on Greenland may be causing small local earthquakes. If so, would this also be considered “perturbations” that could enhance the “Jakobshavn effect”?
Aside from this I just read about the storehouse of methane possibly opening from Siberian methane hydrates (see: http://www.spiegel.de/international/world/0,1518,547976,00.html ). This could cause a lot more warming, and if it does, would it be expected that the Zwally effect would overtake the Jakobshavn effect?
Finally, my meager understanding is that a lot of energy goes into melting ice (is this akin to kinetic energy?), rather than heating the surroundings (another reason why in some places in Greenland there might not be warming), but once the ice is melted the energy then goes into the atmosphere and ocean more quickly. That might be wrong, but as long as there is one small ice cube in a glass, the water stays cool, and as soon as that melts away, the water quickly warms to room temp.
20 April 2008 at 8:12 PM
To d. beck, comment #59
When the sea ice cracks open, the temperature of the water below it is so much higher than the air above it, that water vapor is created. At least, that is what seemed to happen in the beginning of April when the cracks really began to open up, and it seems to be very much an ongoing process, judging by the IR satellite photos that get updated every couple of hours — see: http://www.weatheroffice.gc.ca/data/satellite/hrpt_dfo_ir_100.jpg
Also, see the link a guy from Holland posted on my blog showing the current ice situation compared to last year,
from the National Snow and Ice Data Center, Boulder, Colorado:
http://nsidc.org/data/seaice_index/images/daily_images/S_timeseries.png
Let’s face it, you expose above freezing temp water to dry air that is at 10 degrees Fahrenheit — what is gonna happen?
There are so many cracks now that it is difficult to see what is going on, but it was very clear a few weeks ago.
Also, if you happen to get a chance to look at a good google map that shows the topography around the coast of Greenland, you will get a good shock — the place looks like it is just made for ice to slide out of it.
20 April 2008 at 8:27 PM
Re: comment #59
To: d. beck,
sorry, that was the wrong link — this one is to the Arctic:
http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png
20 April 2008 at 9:55 PM
Gavin, how many computer models actually incorporate the predicted increase of CO2/CO and CH4 and fine particulate smog from china and india and the other developing countries over the next 50 yrs. even if the US went cold turkey tomorrow re: emmissions, that would be cold comfort if china and india continued along their merry way.
20 April 2008 at 10:44 PM
I wonder if it is necessary to invoke the Zwally effect every time one sees a sudden advance of a glacier. Recrystallization of ice due to local strain accumulation or presence of water can shift the primary deformation mechanism from dislocation creep to some other mechanism, such as diffusional creep or superplastic creep. David Goldsby, now at Brown University, has done some wonderful research where he identified a grain boundary sliding (GBS) mechanism in ice, accompanied by dislocation motion.
20 April 2008 at 10:45 PM
Re # 66 Lynn V: “…my meager understanding is that a lot of energy goes into melting ice (is this akin to kinetic energy?)…”
It is called latent heat:
http://en.wikipedia.org/wiki/Latent_heat
21 April 2008 at 7:11 AM
One of the reasons for authoring this post, was a misconception among a number of some glacier scientists even that the Zwally effect was driving the outlet glacier acceleration of the 2001-2005 period. That this is not the case is key to document. It should however, be clear that though we can eliminate that as the key dynamic for acceleration the specific glacier dyanmic underpinnings have not been identified. It is evident that an imbalance at the calving front is one of the key ingredients, but not the only one. Sustaining the observed acceleration for an extended period is difficult, having an outlet glacier better instrumented at the onset of the next acceleration will be a key to fully understanding the process. The widening of the fjord of the Jakobshavn Isbrae above the 2006 terminus can lead to additional calving and further thinning. To what extent I will not hazard an estimate at this moment. It will be worthy of its own post. It will be interesting to examine Pfeffer at all in that light. Total volume flux is a critical parameter to observe over a long time period. In the 1990 paper referenced for this post we did calculate volume flux. It will be nice to compare to Pfeffer’s new work. This post was focussed specifically on Greenland outlet glaciers, not even Greenland as a whole. Meltwater inputs can and will be more important in others regions of the ice sheet. My main focus in on alpine glaciers not ice sheets normally, and I agree with Pfeffer that for now they remain critical.
21 April 2008 at 11:00 AM
Re #59 True: “What matters is if the melting were to increase significantly”.
Also true: I was removed from federal civil service by NWS (July, 2005). The removal was later reversed
and a retirement certificate by NWS for “30 years of Loyal Service rendered to the government of the United States” was awarded (Feb. 2006).
–
and, “Evaporation is greatest during the winter because of the greater difference
between air and water temperatures” Cynthia Sellinger, deputy director of NOAA’s Great Lakes Laboratory.
http://www.shns.com/shns/g_index2.cfm?action=detail&pk=BADICE-02-05-08
and that cold air and open surface waters in the Upper Midwest
results in water vapor released from lakes and rivers (photos available).
http://www.shns.com/shns/g_index2.cfm?action=detail&pk=BADICE-02-05-08
21 April 2008 at 12:48 PM
I’m afraid I am just not understanding the point here. It is not surprising that thinning would be important in setting at what place an outlet would float, nor that thinning might be increasing at an altitude where snow does not persist year-round. But, it is fairly clear that glaciers do not cease to move once their termination is above sea-level. And it is that aspect of their motion that seems to hold the key for future sea level rise. Is there a process that transports ice to an altitude where it must melt rapidly or will it tend to stick at an altitude where it must melt slowly? Whether that lower rapid-melt altitude is sea level or not does not seem to be the key issue: something made Jakobshavn thin so that it floats. Once it floats, who cares? It’s gone already. That Jakobshavn thinned is important because it indicates that at whatever rate it is being fed, it is melting faster than it is piling up. If it happens to be fed at a faster rate from higer altitudes with insignificant thinning owing to melt, but rapid mass transfer owing to melt lubrication then this seems to me to be the more important effect.
Maybe I’ve missed something? Tad Pfeffer (#9) seems to insist that only marine grounded outlets are important, but then points to all the other non-Greenland or Antarctic ice as being more important at present. Many of these reach the sea through rivers, not glaciers.
21 April 2008 at 1:02 PM
Have I gone blind?
What I am not seeing here is a discussion of the recent reports of supraglacial lakes’ hydrofracture of kilometer thick ice resulting in the advection of heat to basement ice. This means the basement ice suddenly warms, and warmer ice is weaker. Weaker ice under the stress of supporting kilometer(s) of ice is subject progressive collapse energetically driven by the potential energy of the supported ice structure.
The result is a slurry of ice and water, moving at a high speed. The high speed is generated by the release of kinetic energy as the face of the (warmed and now weak) basement ice progressively fails under the weight of the ice above. I call this the “Missoula effect.”
The Missoula Effect could move a lot of ice, water, (and rock) through a narrow outlet rather rapidly. If the material still has any significant speed when it gets the shore, it can cause a tsunami.
OK, we have not seen this example of physics in a while. On the other hand, we have not had big chunks of ice suddenly warming in a while either. Now, we are back to a situation where big chunks of ice are suddenly warming.
21 April 2008 at 1:31 PM
Chris, the large Greenland outlet glaciers are not thinning significantly via melting, it is by moving faster and calving more rapidly. It is much faster to lose mass via calving than melting. Note the breakup of Larsen B or the disintegration of the terminus reach of the Jakobshavn from 2001-2006. What matters for calving rate is only if the front of the glacier is afloat. The key for future sea level rise rate of the large ice sheets is not in place melting, but calving.
21 April 2008 at 2:37 PM
Chris Dudley:
Most of the potential for catastrophic sea-level rise in this century lies in the GIS and WAIS, which are both mostly grounded below sea-level. The centre of the WAIS is grounded kilometres below sea-level.
21 April 2008 at 3:05 PM
What Aaron Lewis was mentioning is this:
http://www.whoi.edu/page.do?pid=7545&tid=282&cid=40786&ct=162
News Release : Lakes of Meltwater Can Crack Greenland’s Ice and Contribute to Faster Ice Sheet Flow
Researchers Make First Observations of Surface Meltwater Cutting through the Ice Sheet to Lubricate the Bottom
Mauri Pelto says:
The key for future sea level rise rate of the large ice sheets is not in place melting, but calving.
First, for the glacial and small icecap melt, the 50-70 cm of sea level rise is all mostly inplace melting, not calving, right? So, while you qualify with “large ice sheets”, if the issue is how fast sea level will rise then inplace melting is playing the key role right now.
Second, isn’t there a tendency for glaciologists to neglect the effects of changes in the global planetary circulation (i.e. oceanic and atmospheric heat transport to poleward regions)? This is an area that glaciologists traditionally don’t study - but it seems possible that a warming ocean and atmosphere could indeed lead to high rates of in-place melting.
Another thing is that glaciologists seem to be relying fairly heavily on past records of change - but according to the ice core CO2 measurements, the increase in CO2 is now 30X greater, rate-wise, than anything seen in the record. Thus, we might see things happening on a very fast timeframe relative to what has happened in the past.
P.S. I’ve been trying to figure out what the relative contributions to sea level rise are between large ice sheets, mountain glaciers, and thermal expansion, and I get 0.35 mm/yr, 2.3 mm/year and 0.40 mm/year, based on the papers linked to. Tad Pfeffer says it is 24% glaciers and 14% for ice sheets, leaving 62% for thermal expansion - the numbers I came up with were more like 75% glaciers, 13% thermal expansion, and 12% ice sheets… any comments that might clear this up?
21 April 2008 at 3:07 PM
My understanding has always been that ice masses, whether ice sheets, ice caps or linear valley glaciers, are divided into zones of accumulation - where ice formation from compressed annual snowfall is greater than melting and evaporation - and ablation zones - where melting and evaporation exceed snowfall and ice formation. Between the two zones is the equilibrium line which in detail varies in location season to season and year to year, but in the longer term either moves higher up the valley glacier or further towards the centre of the ice sheet/cap. Because there is a pressure gradient between the accumulation and ablation zones, the ice moves from te first to the second - from effectively the centre to the edge of the sheet. Movement almost always occurs - even if the ice mass is totally frozen to the bedrock, the upper layers are able to slide by plastic deformation et al over the lower layers; however the movement will be more rapid if the lowest layers melt due to the pressure of the overlying ice, to geothermal heat leakage, and to meltwater from the surface reaching the ice base.
What I am not aware of from the scientific literature is whether there is any evidence of the shrinkage of the accumulation zones on the Greenland or even Antarctica ice masses - whether the equilibrium line is contracting towards the centre of the ice sheets. Ascertaining this would involve a calculation of the mass gain and loss of ice over large areas. Can this be done? Has it been done? - by remote sensing perhaps, or detailed long term measurements at random locations scattered across the ice sheets. It is a matter of speculation whether air masses, warmer now in consequence of global warming processes, carry moister air into the centres of ice masses (warmer air has a greater potential capacity for water vapour than cold). This might result in an actual increase in ice formation in the accumulation zones; at the same time, the warmer air might cause more rapid melting and evaporation and iceberg calving at the margins of the ice sheets. The result would be a steeper lateral pressure gradient within the ice between the accumulation and ablation zones, which in turn would bring about greater ice velocities as recorded at so many valley glaciers and ice sheets/caps around the globe.
21 April 2008 at 3:44 PM
A loss of 200 km3 per year from the total 2,650,000 km3 to 3,000,000 km3 of total ice in Greenland is only 0.007% per year.
At that rate, it will take 13,000 years for all the ice to melt.
Increasing sea levels by 0.6 mm per year, it will take 1,600 years to raise sea level by 1 metre.
Basic math indicates that everyone is making this issue out to be way more serious than it is.
[Response: Hmmm…. and so you expect the ice loss rate to stay constant even as temperature rises? And you aren’t concerned about the Eemian sea level rise (4 to 6 meters) with only a few more degrees warmth around Greenland? - gavin]
21 April 2008 at 4:34 PM
Re #80 John Lang - that it will take 1,600 years to raise sea level by 1 metre and 13,000 years for all the ice to melt - basic maths calculation. True - if you assume the ice just stays where it is - which it doesn’t. It slides out from the centre of the ice sheets towards the warmer margins - and it will probably slide out faster the warmer the climate gets - see #79. In other words, glacial melting may be an accelerating process. And this acceleration is likely to be accentuated by the replacement of white snowy/ice surfaces by darker bare rock - and also the rise in sea level prises up or floats the snouts of glaciers and the ice sheets initially anchored to the sea bed, exposing more of the ice bottom surface to melting effects and increasing the downslope velocity of the ice from the interior of the land mass. More and more feedback effects of this nature may be responsible for ever more rapid melting, quite probably at rates far greater than the 200 cubic metres a year quoted in #80.
21 April 2008 at 5:13 PM
Re #60 — change in w (omega or rotation of earth). From moment of inertia: dw/w = - dr/r assuming conservation of rotational energy and mass. One possible explanation of dw being negative (slow down) is that dr is positive, namely increase in r due to expansion of ocean (not redistribution of mass) due to increase global T (as already measured). There are probably many other, perhaps more valid, hypotheses.
jgradie
21 April 2008 at 5:22 PM
Oopps! My comment should have referenced #64 not #60
21 April 2008 at 5:30 PM
At that rate, it will take 13,000 years for all the ice to melt.
The Hansen (et al) paper last summer completely discounted a period of thousands of years for a calamitous sea level rise. Of the 3 broad spans - decade, hundreds, and thousands - they found hundreds to be most likely and couldn’t rule out a period of decades once broad scale melting was under way. The two of you might be arguing two related things. Your statement was for “all” Greenland ice melt, and the Hansen paper just examined the scale of time for sea levels to rise calamitously. As for the difference, if Florida winds up looking like a wasp stinger, I won’t begrudge Greenland it’s remaining ice.
21 April 2008 at 7:02 PM
Good question Mike. In the case of Antartica there is not a substantial traditional ablation zone. Mass loss is dominantly via calving and sublimation. Ice shelves in particular are not compatible with ablation zones. On the Greenland Ice Sheet the extent of the area experiencing ablation is determined each year using passive satellite microwave data which distinguishes wet snow from dry snow. http://cires.colorado.edu/science/groups/steffen/greenland/melt2005/. It is evident that in the short record available the mean extent has expanded. You are correct that if accumulation increases and ablation increases, the higher balance gradient would necessitate that the glaciers accelerate. It is not evident that the balance gradient has steepened significantly. Even if it does, a large ice sheet outlet glaciers response time is not rapid for such a change to propogate downglacier in the time interval for which we have data. A steeper balance gradient cannot be responsible for the recent observed accelerations. An acceleration from a steeper balance gradient would not be at its maximum at the terminus either. It would be at its maximum near the equilibrium line, where no notable accelerations have been observed.
21 April 2008 at 7:18 PM
Mauri and Nick,
Thanks for your responses. I can understand that a uniformally accelerating glacier would thin regardless of melting. I had been thinking that in the case of 25 meters of sea level rise over a few centuries (3 oC of warming), perhaps most of the melting in Greenland would occur on land at low altitude rather than in the sea. But, perhaps the transition would not occur in this century as Nick suggests.
I guess what I am still not understanding is: if the surface melting and resulting lubrication is the origin of the acceleration at the outlet, is not the thinning there better thought of as a result of the increased pressure rather than the “plug” being somehow diminished? What is going on upstream seems more important.
21 April 2008 at 7:43 PM
Gavin, You continue to say that current sea level rise is 3 to 4 mm per year. However NASA says since 1992 average is just at 3.05 mm and over the past year there is really no rise or possibly a fall http://www.aviso.oceanobs.com/en/news/ocean-indicators/mean-sea-level/index.html Other types of measurements have run about 1mm to 2mm per year. You are also surely aware that NASA’s Argos system found no rise in sea temperature in the past five years http://www.npr.org/templates/story/story.php?storyId=88520025 and the U.N. admits there has been no atmospheric increase in temperature since 1998 http://www.ibdeditorials.com/IBDArticles.aspx?id=292204249288396
21 April 2008 at 9:04 PM
Dear Pat (#73) and d. beck (#59),
I think that the point that I am trying to make is this:
That very thin new Arctic sea ice has pretty much been going all to smitherines over the last 3 weeks, and tons of water vapor has been created, which has to go somewhere, and the part of it that ends up hanging over Greenland can hasten the melting, and it can even cause rain. (I think I read somewhere last year that it actually rained on Greenland at altitudes previously thought unlikely.)
Of course, this cracking up of the sea ice goes on each summer, but now it is occurring earlier in the year and faster over a much greater extent.
OK, and this is weird: I just looked at the sea ice extent graph, and the updated graph from today shows completely different data compared to yesterday’s graph. That’s a really big change. Fortunately, I saved a copy of yesterday’s graph on my HD, which I will copy both to my blog — I think we all deserve an explanation from the National Snow and Ice Data Center.
http://climatechangepsychology.blogspot.com/2008/04/national-snow-and-ice-data-center-graph.html
21 April 2008 at 9:06 PM
87:
The ocean temperature that matters for sea level rise would be the (coefficient of expansion weighted) average sea temperature. Only a tiny fraction of this water is close enough to the surface to be measurable by sea surface temperature observations. If indeed sea surface temperatures have in fact stabilized (this is likely a temporary effect) the conduction/advection of heat into the deep oceans would still continue for many hundreds of years. It may be possible to indirectly measure ocean basin average temperatures by sound travel times. In principal gravity measurements would do the trick, but I suspect the noise due to ordinary geological processes might overwhelm the warming signal.
21 April 2008 at 10:02 PM
Re #88
“OK, and this is weird: I just looked at the sea ice extent graph, and the updated graph from today shows completely different data compared to yesterday’s graph. That’s a really big change. Fortunately, I saved a copy of yesterday’s graph on my HD, which I will copy both to my blog — I think we all deserve an explanation from the National Snow and Ice Data Center.”
I noticed the sudden downturn on the graph yesterday and also that it coincided with images that were missing signal in a couple of regions. I anticipated that the graph would shortly be adjusted and as you have shown they were.
22 April 2008 at 12:55 AM
Aaron Lewis (#75)
Storm tracks will be moving progressively north over the course of the century, more rainfall at higher latitudes — not to mention the polar amplification and extended “growing” (”melting”) season. Rain and ice makes slush. Of course what I am wondering about is on the other side of the earth, where ocean currents are circulating more heat content to greater depths, where rivers run under glaciers, the base of which are below sea level — particularly along the West Antarctic Peninsula.
Additionally, the deeper the heat content goes, the more likely it would seem that it will destabilize methane cathrate deposits sooner rather than later. Not that I have heard anything about such deposits there, but higher oxygen content in the water implies more organic material, which means more material from which to generate methane. And we have found plenty of such deposits in the Arctic region.
22 April 2008 at 1:24 AM
Thanks Gavin, I thought you were on vacation or something.
22 April 2008 at 3:34 AM
Tenney@88:
Yes, I noticed the NSIDC graph change too. I assume that the earlier graph, which was extreme, was a data processing error. The current graph is still plenty alarming.
These things happen at the cutting edge. We had similarly alarming sea ice area graphs from Cryosphere Today for a short while earlier in the year, before they found and fixed a bug.
22 April 2008 at 6:33 AM
Aaron 75, your description takes my concerns a useful step further, as you have identified a collapse mechanism for deep warming ice. As you say if there is water flowing beneath ice then the roof of ice over that flow is warming, and that heat will move upwards progressively weakening and softening the ice mass – even though the ice near the surface looks ok.
Your Missoula Effect sounds like a classic non-linear response. I think the risk posed by these effects utterly overwhelms concerns over calving vs melting.
The recent discoveries of great rivers flowing beneath EAIS and WAIS – including vertical surface movement of plus/minus 3 metres in a matter of a few weeks on ice sheet surfaces which were coupled with changes in basement water flows demonstrates that the security of grounded ice is a myth. Where water flows there energy flows.
The grounded ice can still be full of voids above sea level that allow melt water to circulate bringing its energy contribution, and below sea level where melt water runs out as basement flows under upstream pressure and sea water flows in and out under tidal differential heads. Any crack in the ice joining with the ocean will be influenced by tidal effects, and these cracks will not self-heal. They will widen laterally as the sides and base melts away, and as the ceiling takes heat out of the water vapour. Below sea level water circulation within the grounded ice mass can also be driven by salinity and temperature gradients.
It is not hard to envisage an ice sheet like a hair-brush sitting with its bristles in the water, and the back of the brush being the above high tide solid ‘lid’ on a very unstable structure.
22 April 2008 at 7:05 AM
Re #88, even without the strange downward line on the olf chart the nww chart seems bad enough and that downward turn could perhaps be significant becaue the ice cannot reform until next winter once gone I presume?
22 April 2008 at 9:40 AM
Chris the point you miss, is that it is not the surface melting that has driven the acceleration. End of story. It is not what is happening upglacier that has been the key. If either was the case then flow would be higher in the summer and acceleration would not have begun at the calving front. Get rid of your false assumption that the meltwater is driving the acceleration. Aaron and Nigel: If you look at the 1962 maps of Greenland or any satellite image from the 1970-1990’s period, the glacier lakes are present. They can deliver some heat, but it is not a new phenomenon. Their extent and volume you would think would be increasing, but this has not been documented. Thus, we do not have a mechanism for additional significant basal warming. The water at 0 C also cannot warm the basal ice which is at the pressure melting point much.
22 April 2008 at 9:44 AM
There’s a lot written about heat from friction at the glacier/rock interface; don’t assume a glacier is cold at the bottom, it may be warmer.
Some tidbits: http://www.agu.org/meetings/fm06/fm06-sessions/fm06_C53A.html
“Warm based glaciers are at the pressure melting point at their bed. Heat from the Earth and from basal friction provides energy to melt ice at the bed, …”
www.homepage.montana.edu/~geol445/hyperglac/morphology1/
And I’ve been getting in William’s hair* about this over at Stoat http://scienceblogs.com/stoat/2008/04/dont_believe_a_word_of_it_guv.php#comments
————-
*If I have seen further than others, it’s by getting in their hair
22 April 2008 at 9:58 AM
I have a question about this part of the post:
“The second mechanism is a ‘Jakobshavn effect,’ coined by Terry Hughes (1986), where a small imbalance of forces caused by some perturbation can cause a substantial non-linear response. In this case an imbalance of forces at the calving front propagates up-glacier.”
But, we know that Dr. Robert Corell witnessed a “substantial non-linear response” to something when 5 km of the Ilulissat glacier roared past in only 90 minutes.
And, while presently it appears that events at the front of the glaciers are the significant areas, won’t it actually be the effects of things such as glacier lake collapses upstream that become ever more frequent and thus more significant, as time goes on?
22 April 2008 at 10:06 AM
Re: #95
Pete, the remnants of the older sea ice have all already broken up and appear ready to weaken substantially.
What I would like to know is if long-term, time-series data are available concerning the temperatures of the Northern Ocean, at various depths (surely the U.S. Navy has something on this), and/or if there are in place instruments to measure these temperatures this year and in the future.
22 April 2008 at 10:09 AM
Re: #96
Sorry Dr. Pelto, I missed your remark about the glacier lakes. But the number and size of the moulins are increasing somewhat exponentially, are they not?
22 April 2008 at 10:52 AM
Another contributing factor here appears to be the Arctic Spring Haze of airborne pollutants -
http://www.sciencedaily.com/releases/2008/04/080407132120.htm
Warming air melts the ice faster, thin ice is blown apart by the winds and currents in the Arctic Ocean, leading to large areas where the ocean can freely exchange heat with the atmosphere (the rate being dependent on wind and other factors - for more see http://eesc.columbia.edu/courses/ees/climate/lectures/o_atm.html ).
The actual effect of all that is not intuitive, but has to be analyzed using computers for data collection, data analysis and modeling. A lot of “skeptics” don’t seem to understand the basic process of model design and refinement - make a model, see what it misses, refine the model, see what it misses, and keep iterating. It is not a “curve-fitting process” - real data is used to initialize the model, but then no comparison is made to the real data until afterwards. So, the question is, has anyone made a model, which, when initialized with say, 1980 conditions, predicts the rapid loss of sea ice in the Arctic? Such a model might have a difficult time predicting the amount of Arctic spring haze pollution each year - so that might be an external variable, set by the researcher.
It’s also worth looking at some glaciers that are not going with the overall melting trend:
http://www.springerlink.com/content/a3581383141m4126/
Howat et. al 2006: A precipitation-dominated, mid-latitude glacier system: Mount Shasta, California
So, that’s a very useful number - 1C rise in temp must be countered by a 20% increase in precipitation. Is it widely applicable, or limited to mountain glaciers, or to Shasta in particular?
22 April 2008 at 11:08 AM
Re 91
Greenland has the potential to make its own weather. It rises to produce orogenic precipitation, whchever way the wind blows. Its ice provides a temperature diferential to steer winds from either the North Atlantic or the newly ice free Arctic Ocean.
These days, I think of Greenland less as a pile of ice accumulating snow, and more as a water shed with a summer (March to November) rainy season - with no plants to retard runoff. Where does that water go? How much energy does water flowing through a moulin release?
22 April 2008 at 12:08 PM
Re #101
Regarding the comments about arctic haze, our ‘Johnny on the spot’, Wayne Davidson has been observing very clear skies for the last couple of years and associates that with the warming and melting.
http://www.eh2r.com/
Regarding the 1º/20% increase number I would expect that to be site dependent although there must be a link everywhere.
22 April 2008 at 1:54 PM
Mauri Pelto,
Thanks for the article and your active involvement in this thread.
#87 Gary,
Didn’t you think to check around for the uncertainty involved in the 3.05mm/yr you quote? Or do you really think it’s 3.05 exactly with no uncertainty?
From IPCC AR4 Chapter 5
http://ipcc-wg1.ucar.edu/wg1/wg1-report.html
“Numerous papers on the altimetry results (see Cazenave and Nerem, 2004, for a review) show a current rate of sea level rise of 3.1 ± 0.7 mm yr–1 over 1993 to 2003 (Cazenave and Nerem, 2004; Leuliette et al., 2004)”
So that’s 2.4 to 2.8mm per year. If you’re worried about supposed IPCC bias you may want to try reading the references from which those AR4 statements are drawn.
The second item you link to merely shows that a lot of work is being done by the experts, so it is pointless to draw conclusions at this stage with respect to Argo, deployed in 2003. However it should hhave been apparent to you from your first link that the altimeters show a sea level rise from 2003 to 2007 at the same rate as previously. And the previous rise was in part due to thermal expansion. So if the oceans have really cooled…
Well it’s discussed in the article, which is an interesting lay person’s read through to the final paragraph(hint).
Sorry but the Investor’s Business Daily page at the end of your final link is a complete joke (It’s your use of it that suggests to me you’re in denial. Getting suckered by such carp is almost on the same level as believing a schoolkid can undermine a whole branch of science.)
You state “the U.N. admits there has been no atmospheric increase in temperature since 1998″ The Investor’s Business Daily(IBD) article you link to implicitly supports this contention. Yet it is only the article itself that makes this incorrect assertion, not the UN!
Have a look at the CRU global average temperature: http://www.cru.uea.ac.uk/cru/data/temperature/nhshgl.gif Have a look at that graph, it’s telling the true sceptic something crucial. (scientists should be sceptical, denialists cling to their precious beliefs in the face of evidence)
By any of the 3 main datasets it is clear that 1998 was an outlier, this is accepted, it is only those in denial (like the author that article) who make a straw man of 1998. i.e.
From the IBD article:
“If that’s the case, then why can’t the Pacific’s El Nino current, which played a large part in the warm reading for 1998, simply been seen as a “variability” and not part of a greater warming trend? Because it doesn’t fit the agenda?”
To which I answer:
“El Nino IS seem as natural variability, you dolt.”
It would be correct to say “global average temperature remains below the 1998 peak in the CRU dataset”. But it is clearly wrong to say “There has been no increase in global average temperature since 1998.” Both of those statements are factual and as Mark Twain once said (paraphrased); a person is entitled to their own opinion, but they are not entitled to their own facts.
Click on this link http://data.giss.nasa.gov/gistemp/m