Mechanical erosion of ice sheets

[Gray-Wolf]

G-W; there's no argument about your underlying concerns with the stability of the WAIS; it's the whole issue of timing and forcing which is the key question here, I'm sure you'll agree.

P

Hi P3, my last comment isn't a dig at anyone , I just can easily fall foul of my own, internally generated 'self doubt'.

As you rightly point out many areas of science do not see the problem as 'imminent' but, and this is a big but, if we see 'worrying trends ' within 'stable' (apparently) ice sheets/shelves then more areas of science may need to look at 'catastrophic failure' as a real mechanism for rapid ice ablation in the Antarctic/Greenland Ice sheets.

Some of the 'paleao records' point to rapid changes of this kind (with climatic changes 'forced' after collapse) and I just hope that warming oceans were not the 'trigger'.

[parmenides3]

Thanks to one of my favourite blogs, Rabett Run, http://rabett.blogspot.com/ I find that G-W is not alone in his concerns about ice sheet collapse. Apparently, Jim Hansen (the 'godfather' of CC?) also has real concerns about the possibility of this event. The blog provides a very useful link to Hansen's lecture notes on dangerous climate change from a lecture he gave last week. As it is unannotated, it gives an interesting perspective on what is being looked at and how the numbers appear to stack up. Unfortunately, there isn't much data on the ice sheets, apart from a graph from 2005's analysis of Greenland ice sheet mass balance.

Hansen is calling for the National Academy of Science to institute urgent research into the ice sheets, arguin that waiting for the IPCC to get anything organised may take too long. He seems to be ignoring the fact that this is International Polar Year, though, which should involve some new material being published.

I don't think he is expecting the ice sheets to reach 'meltdown' (excuse the pun) imminently, rather that it seems likely that a relatively small increase in global temperature (1C) could be enough to tip the balance.

More on this as it becomes available.

:)P

[Devonian]

I don't think he is expecting the ice sheets to reach 'meltdown' (excuse the pun) imminently, rather that it seems likely that a relatively small increase in global temperature (1C) could be enough to tip the balance.

Which is at least evidence that 2C might well be serious

[parmenides3]

Which is at least evidence that 2C might well be serious

Just a quick reminder: as I said on the post in the other thread, the comments weren't to be read as my personal opinion on how much the climate is changing, or on how much we are responsible for changes; it was an exercise in rational scepticism, no more. Hansen stands out at the moment as one who thinks that CO2 emissions need to be stopped at 450ppm, rather than allowing them to double. Much of his recent published material is along these lines. He also takes the unusual step of offering an opinion (not an 'official' one) on what action needs to be urgently taken to reduce the risk of what he sees as dangerous change.

It is Hansen's view that a 2C rise in temperature from pre-industrial values should be the upper limit of what we should think of as 'acceptable'. Even then, he points out, we may have started something bigger than we currently realise.

Personally, I can't see how we are going to stop emissions rising beyond 450ppm, even 550ppm, with any of the current strategies or policies. Unless there is a dramatic change in the real world, I'd suggest that 700ppm by 2100 is not unlikely, though by then, the rate of increase should have slowed somewhat.

Going from the 'official' estimates of climate sensitivity and the 'official' projections of warming, this would raise global temperatures by something nearer to 4C (by 2200) than the 1 or 2C being bandied about here. Would this be 'dangerous'? It's hard to find a reason to believe that it wouldn't be a serious problem.

:)P

[Devonian]

I absolutely agree P3 , with both you and Dr Hansen

[parmenides3]

I, too, am inclined to agree with Hansen, but I remain to be convinced, as yet. Still open-minded on the subject.

:)P

[Gray-Wolf]

2c puts us within the climatic range of the Eemian epoch (125,000yrs ago) ,but then sea levels were 5m higher....I wonder how that could have happened?

Edited March 2, 2007 by Gray-Wolf

[trevw]

thought this was an interesting article - is about the grounding point and what it might take to float the ice off its grounding point..

http://earthobservatory.nasa.gov/Newsroom/...7030124445.html

Trev

[Gray-Wolf]

Indeed Trev! I'd looked over it earlier and there currently seems to be a mass of papers coming from the Antarctic (maybe we only get reports during the Antarctic summer?)

Another paper from Geophysicists Robin Bell and Micheal Studinger from Lamont-Doherty Earth observatory (Columbia /uni, New York City) point out how little we know about rapid deglaciation but flags the impact sub glacial lakes/ ice streams in facilitating 'climate changing' pulses of melt water outflow

"floods have been known to originate from the interior of the ice sheet in the past, possibly from systems like these sub-glacial lakes. These sudden outbursts of fresh water could potentially interfere with nearby ocean currents that redistribute heat around the globe and could disrupt the Earths climatic system"

Now why doesn't this surprise me? A quick look at SST anomalies from the Ross sea north to New Zealand is why!

[Gray-Wolf]

Indeed Trev! I'd looked over it earlier and there currently seems to be a mass of papers coming from the Antarctic (maybe we only get reports during the Antarctic summer?)

Another paper from Geophysicists Robin Bell and Micheal Studinger from Lamont-Doherty Earth observatory (Columbia /uni, New York City) point out how little we know about rapid deglaciation but flags the impact sub glacial lakes/ ice streams in facilitating 'climate changing' pulses of melt water outflow

"floods have been known to originate from the interior of the ice sheet in the past, possibly from systems like these sub-glacial lakes. These sudden outbursts of fresh water could potentially interfere with nearby ocean currents that redistribute heat around the globe and could disrupt the Earths climatic system"

Now why doesn't this surprise me? A quick look at SST anomalies from the Ross sea north to New Zealand is why!

EDIT: Bleeping edit feature!

The thing with the 'sediment stablisation' is that it does not deal with 'meltwater pulses' which are vast outpourings leading to large scale erosion (I would imagine glacial rubble,sand and varves ore not hard to erode in such instances!) but only with "Sea level change".

There seems to be a 'spurt' of research into the rapid collapse of ice sheets/shelves and all are consistantly pointing to massive failure instigated by liquid water at the sheets/shelves base (be it geothermaly generated or pressure generated) so the 'grounding' of shelves on their own detritus does nothing to calm my concerns!

[parmenides3]

Here's a nice new resource to play with: http://www.cresis.ku.edu/research/data/sea...rise/index.html

The sea level rise graphics are very detailed, but be warned; the pdf files are very large. There's a link to stuff the whole thing on Google earth, too.

In the research section there are a couple of interesting papers (e.g. Rignot et. al. (2005)) on the Antarctic.

:)P

[Gray-Wolf]

Saw a prog last night about a giant flood/s in the scablands of Washington state which were brought about by an ice dam collapse (and so not just the Icelandic research into Ice Dam Collapse points to this a an ice 'dynamic').

From watching the prog I realised that we didn't want to recently be measuring ice lakes filling and emptying across Antarctica. The prog made very clear the corrosive nature of supercooled water at pressure and it's exploitation of 'weaknesses' within the basal horizons of ice sheets/glaciers so to now be measuring huge quantities of the stuff at play beneath both sheets and Glaciers there twinges my worry bone!

[Gray-Wolf]

Well ,that seems to be it for the Antarctic as the seas are starting their winter freeze and the first snow obliterate 'my crack'.

From now on I'll be looking at the effects of winters storms/warmth on the Arctic melt season, I kinda figure that around Svalbard it never really got going due to warm water plumes and wave action.

The opening up of 'Polynya's' in the area facing the Bearing Sea will be of interest (to see if last years weakness promotes earlier formation or not) but also our northern fringe of the Atlantic because of the stormy/warm winter.

We'll also see how quickly 'year ice' (waters frozen this season) respond to the melt as some areas have ice cover up to 71-2000 'average' extents but only of 'year ice'.

[Devonian]

Linkable to this thread I think - another report on changes to the ice on Antarctica.

Edited March 23, 2007 by Devonian

[Gray-Wolf]

Linkable to this thread I think - another report on changes to the ice on Antarctica.

Thanks for that Devonian! I've mooted before that I found it hard to understand the IPCC's backtrack on sea level change in their latest report whist we know that during the Eemian (125,000yrs ago) with temps 2c up on todays, we had sea levels up to 4m higher.....70cm with a 4c change indeed!!!!!

[parmenides3]

Thanks for that Devonian! I've mooted before that I found it hard to understand the IPCC's backtrack on sea level change in their latest report whist we know that during the Eemian (125,000yrs ago) with temps 2c up on todays, we had sea levels up to 4m higher.....70cm with a 4c change indeed!!!!!

G-W: the IPCC AR4 hasn't 'backtracked' on it's sea level rise predictions; it has taken out the currently very uncertain effects from the ice sheets which were included in the TAR. On the other hand, it hasn't addressed the ice sheet question at all, at least, not in the SPM.

Here's a new paper on the freshening of Antarctic bottom layer water. I have no idea of it's implications but it is, as I said, at least interesting:

http://www.agu.org/pubs/crossref/2007/2006GL028550.shtml

:)P

[Gray-Wolf]

Thanks P3!

If I am right in assuming that the 'freshening' is due to an increased in the melt (fresh) water replacement rate in those areas then it does add to my belief that the cold water anomalies this late winter (in the regions mentioned in the article) over the 'shallow' basins like the NZ shelfs and the Antarctic ridge were driven by the denser ,colder Antarctic outflow.

For it to have influenced the upper horizons of the Oceans there must indicate a step change in the volume of cold, fresh water outputting from both East and West Antarctica via the Ross sea.

If this is the case then I expect in late summer there will be rumblings of the same within the Scientific community. This paper, coupled with the recent ice lakes/streams papers seems to prepare the 'groundwork' for further 'revelations' raising the profile of increased basal freshening within that area.

EDIT And overturning the El Nino in late Feb.............though that may be stretching things a teensy winsy

Edited March 27, 2007 by Gray-Wolf

[parmenides3]

It occurs to me that I have seen little discussion of estimates of subsurface freshwater inpout from the Antarctic into the ocean systems so far; one wonders if this has been somewhat overlooked. As very little is overlooked, though, I think some digging is in order.

I still say it's too early to talk about a 'step change' - there simply isn't enough evidence for this (yet).

:)P

[Gray-Wolf]

Parenting seems to be swamping studies for me at present, normal service will be resumed when he's at Uni' (in 14yrs).

So far as study of freshwater,dense, outflow there must be measurements taken already that would help us 'imply' outflow changes/amounts whilst not directly measuring it ? Maybe it's staring us in the face but we are just not looking for it.

10yrs ago we were treated to Sat. measurements of ice increase at the continental centre. Last year we were treated to fluctuating ice heights due to sub-surface lake fillings and emptyings. Do the later measurements bring into question the validity of the earlier 'measurements' of height fluctuations or are the two unrelated?

South Island NZ were treated to a 'every 70 years or so' spectacle of giant bergs off shore followed by the coldest summer in 14yrs whilst cold water anomalies surrounded the islands most of their summer (anomalies you could see as contiguous with the cold water anomalies from the Ross sea) any hints there???

Edited March 29, 2007 by Gray-Wolf

[jethro]

Parenting seems to be swamping studies for me at present, normal service will be resumed when he's at Uni' (in 14yrs).

So far as study of freshwater,dense, outflow there must be measurements taken already that would help us 'imply' outflow changes/amounts whilst not directly measuring it ? Maybe it's staring us in the face but we are just not looking for it.

10yrs ago we were treated to Sat. measurements of ice increase at the continental centre. Last year we were treated to fluctuating ice heights due to sub-surface lake fillings and emptyings. Do the later measurements bring into question the validity of the earlier 'measurements' of height fluctuations or are the two unrelated?

South Island NZ were treated to a 'every 70 years or so' spectacle of giant bergs off shore followed by the coldest summer in 14yrs whilst cold water anomalies surrounded the islands most of their summer (anomalies you could see as contiguous with the cold water anomalies from the Ross sea) any hints there???

GW, a totally off the wall thought, quite possibly complete balls but.....whilst digging around the Net trying to find info on Carbon 14 I read quite a few sites about Nuclear Testing trying to find out how much extra C14 was thrown into the atmosphere at the time - pre test ban treaty. It appears the Russians detonated quite a few large, megatonne, nuclear bombs underwater. Can't remember where, but should be fairly easy to find out with some digging. If it was anywhere near the Artic, what effect do you think it could have had? Can't have been a positive one. Could it have started/stepped up erosion? All that energy released has got to have warmed sub ocean surely?

[parmenides3]

GW, a totally off the wall thought, quite possibly complete balls but.....whilst digging around the Net trying to find info on Carbon 14 I read quite a few sites about Nuclear Testing trying to find out how much extra C14 was thrown into the atmosphere at the time - pre test ban treaty. It appears the Russians detonated quite a few large, megatonne, nuclear bombs underwater. Can't remember where, but should be fairly easy to find out with some digging. If it was anywhere near the Artic, what effect do you think it could have had? Can't have been a positive one. Could it have started/stepped up erosion? All that energy released has got to have warmed sub ocean surely?

Mostly around Novaya Zemlya (Kara Sea). Not sure what effect you would expect it to have.

It had also occurred to me that people are quite reticent about C14 levels since 1953, and that there should be some residual in the atmosphere, but the info may still be classified. Glad to see you've been doing your homework. :)P

[jethro]

Mostly around Novaya Zemlya (Kara Sea). Not sure what effect you would expect it to have.

It had also occurred to me that people are quite reticent about C14 levels since 1953, and that there should be some residual in the atmosphere, but the info may still be classified. Glad to see you've been doing your homework. :)P

Do I get a gold star? You're right about the reticence, I've spent hours trawling the net, to no avail so far; onward and upward... I'm sure I've read somewhere about C14, space nuclear bomb testing and climate shift patterns. It is only a vague memory, possibly flawed by the volume of stuff I've read recently, but I think the theory was that land based explosions had less long term impact than the space ones. Land based explosions create the familiar mushroom cloud and are shortlived, comparatively contained, atmospheric wise. The space ones detonated with a huge, flat, round surface over a massive distance and the explosions sometimes lasted as long as 30 minutes! Presumably, all that C14 has got to still be there to some extent? Will it/has it entered our atmosphere?

More digging required. That's all I ever seem to do, digging at work, digging at home, was I spade in a previous life?

[parmenides3]

Found this one especially for you, G-W, thanks to a poster on RC: Secrets of the WAIS..

Apparently, the presentation start about 13 minutes in. Enjoy. :)P

http://www.esi.utexas.edu/walse/

Also note; Amundsen shelf...

Edited March 29, 2007 by parmenides3

[parmenides3]

An entertaining blog, Rabett Run http://rabett.blogspot.com/ has a new entry on Hansen's current paper (in press) on ice sheets and sea level rise. The blog is a response to a piece on Prometheus about Hansen's reference to 'scientific reticence' in the IPCC. Inside is a link to the paper itself, which makes for a rather entertaining read. Hansen is giving the opinion (backed by research) that a 1 metre sea level rise by 2100, due to melting ice sheets, is more than likely. He also points out that, under the BAU scenarios, ice sheet collapse is a distinct possibility. But he laso points out the non-linearit of ice sheet responses to global warming, saying that this both explains the IPCC reluctance to include it in their sea level estimates and explains why increasing CO2 concentrations beyond 450ppm is not advisable.

Another one with G-W in mind.

:)P

[Gray-Wolf]

Found this one especially for you, G-W, thanks to a poster on RC: Secrets of the WAIS..

Apparently, the presentation start about 13 minutes in. Enjoy. :lol: P

http://www.esi.utexas.edu/walse/

Also note; Amundsen shelf...

Well you did it again P3, Excellent work, go straight to the top of the class!!!

As you say they are focused on the more dynamic side of WAIS (up the coast from my little area) but fascinating stuff. Good to see the level of collaboration across the sciences/nations too.

Maybe some of the 'ice sheet thickening wallah's should have a peep to see just why the central area' may be thickening.

This brings me neatly onto the 'thickening' behind the Ross. If there is a 150yr log jam of ice back there then surely it has a 'breaking point' where the pressures exerted (remember those subsurface 'rucks' discovered 2 yrs back?) exceed it's inertia?

The fact that most of the WAIS seems to have an outlet via Thwaites Glacier, and would appear to be 'on with' it's great escape means that most all of Ross is fed by the EAIS and so any changes in it's dynamics/output would really signify catastrophic change (we don't want the EAIS draining off now do we?)

The other point that came across loud and clear was the Human/Natural nature of the WAIS mobility. If the peripheral warming effects far enough back then it will interface with the rift valley system (hot substrata) and 'whoosh', the ice is gone! (maybe a tad over dramatic there....)

Thanks again!

EDIT: and thanks for the blog, am I right to assume that the BAU estimates sre merely a projection of current rates and do not reflect any of the dynamic changes (pulses) of ice ablation? Molly does not thank you as she is now 1hr overdue her walkies.......

Edited March 30, 2007 by Gray-Wolf