Polar Ice: Crushed or Cubed

[Chris Coles]

Re: Polar Ice: Crushed or Cubed

If I have one question here; has anyone presented a detailed paper to describe what was the underlying mechanism that caused the sudden collapse of Larsen B? http://earthobservatory.nasa.gov/Fea...ge/larsenb.php

If we take an analogy of the collapse of the Twin Towers in 2001; is there the same potential for a collapse of the Greenland Ice Sheet where the top layer, of the same thickness as Larsen B, suddenly collapsed upon the underlying 10,500 thick sheet?

Without a full understanding of the collapse of Larsen B, can we be absolutely certain that the same will not apply to Greenland?

Note: I well remember New Scientist the year before, (after the Larsen-A ice shelf had broken up), saying that if the Larsen-B ice shelf collapsed within the next 35 years we should be worried. Larsen-B collapsed within months of their making that statement. Take particular interest in the March 7^th 2002 image showing a huge area has turned to liquid water.

[santafe2]

Re: Polar Ice: Crushed or Cubed

If we take an analogy of the collapse of the Twin Towers in 2001; is there the same potential for a collapse of the Greenland Ice Sheet where the top layer, of the same thickness as Larsen B, suddenly collapsed upon the underlying 10,500 thick sheet?

Without a full understanding of the collapse of Larsen B, can we be absolutely certain that the same will not apply to Greenland?

Chris - It's not useful to conflate climate issues related to floating ice shelves at sea level in Antarctica with glacial climate issues at an average altitude of 7000 feet. Ice shelves calve, (sometimes massively), and glaciers retreat. The massive ice sheet on Greenland has actually depressed the central portion of Greenland to about 300 meters below sea level creating a cupping effect. I know of no serious work that anticipates anything more than a gradual retreat of glaciers on Greenland. While this retreat isn't trivial, it is not related to the massive calving we see with large ice shelves.

Larsen A calved in 1995 and B in 2002. While sudden, the Larsen B event was not a surprise. In the decade prior to 2002, approximately 18 meters of the shelf bottom had been worn away which made Larsen B more buoyant and more likely to become unpinned. There are other processes but essentially the water under the shelf is warmer, the shelf thins, rises and detaches.

There is a full understanding of the collapse mechanisms. Linked below is a peer reviewed paper that examines the Wilkins Ice Shelf. This paper was published the year before the collapse in 2009.
http://www.the-cryosphere-discuss.ne...2-341-2008.pdf

[cjppjc]

Re: Polar Ice: Crushed or Cubed

I think the accepted number regarding temperature change over the industrial period is .8C. or 1.44F. We should be careful to not characterize this as "only".

Do you know if there has been other times where an increase or decrease of this amount has taken place?

[santafe2]

Re: Polar Ice: Crushed or Cubed

Do you know if there has been other times where an increase or decrease of this amount has taken place?

The earth has seen a temperature increase or decrease much greater than this magnitude many times in the past. Three refinements to your question are important. When did these occur, how long did it take to occur and is there external attribution, i.e., not simply natural variability? To parse out the first bit, we probably don't care much about warming or cooling events 4 billion years ago but probably do care about the last 400,000 years. We at least have ice cores as a proxy for temperature and chemical measurement. We really care about the last 10,000 years because that's our time building human societies and while we like to quible about the Little Ice Age and the Medieval Warm Period, all in, it's been a pretty sweet 10,000 years climate-wise.

I assume we're more concerned about temperature rise given our current issue so the next question to ask is how long has it taken in the past for temperature to rise 1 degree C? If we look at the current Interglacial as an example it took about 5,600 years for the temperature to rise 8C or about 1 degree every 700 years. This rise was complete over 11,000 years ago and we've been in a fairly constant temperature band since that time. Here's a good question. If the temperature rise from the peak of the last glacial period 20,000 years ago was 8C, how could we possibly be concerned about a .8C rise over the last 200+ years? This question becomes more focused if we go back to the previous Interglacial and see that temperature rose about 2C higher than it is today. So what's the big deal with another 2C rise in average atmospheric temperature?

This gets us to my 3rd refinement, the issue of external attribution. Scientists largely understand the long glacial and short interglacial periods over the last 400,000 years as a function of natural variability especially as it relates to Milankovitch Cycles, (earth's tilt toward the sun, orbit around the sun and earth's axial precession or propensity to create mild or severe seasons in one hemisphere or the other). But it is difficult and most would say impossible to attribute our little .8C increase in temperature to variability.

So why is the earth warming? Milankovitch Cycles would indicate a long term trend toward cooling. Sun activity has been moving downward for a decade. If we examine peak CO2 level over all of the Interglacial warm periods over the last 400,000 years we see a maximum peak of 300ppm and an average of 285ppm. This is the 5th C02 peak during the ice core measurement era and peak CO2 levels all look about the same. That is until a bit before mid-20th Century. Since that time we've moved up to almost 400ppm and at current rates of increase will be at 500ppm shortly after mid Century and 600ppm by 2100. That begins to look like a serious external climate forcing.

It's unlikely that our little .8C increase plus the .6C increase built into the oceans is where this trend will end. CO2 traps heat, thermodynamics demands that the system be balanced, (the earth has to get warmer to throw off this additional heat), so the earth will continue to warm. How much, how quickly and to what effect is where we should be focused.As measured against other paleo-recent temperature increases, this one is small but the rate of rise is happing on a human time scale, not a geologic time scale. To my mind, it's not likely that this is a trivial event.

[cjppjc]

Re: Polar Ice: Crushed or Cubed

Thank you for the reply. For myself I can never know the answer to the question, is the temperature increase or decrease, part of the evolution of the planet.

[Chris Coles]

Re: Polar Ice: Crushed or Cubed

Chris - It's not useful to conflate climate issues related to floating ice shelves at sea level in Antarctica with glacial climate issues at an average altitude of 7000 feet. Ice shelves calve, (sometimes massively), and glaciers retreat. The massive ice sheet on Greenland has actually depressed the central portion of Greenland to about 300 meters below sea level creating a cupping effect. I know of no serious work that anticipates anything more than a gradual retreat of glaciers on Greenland. While this retreat isn't trivial, it is not related to the massive calving we see with large ice shelves.

Larsen A calved in 1995 and B in 2002. While sudden, the Larsen B event was not a surprise. In the decade prior to 2002, approximately 18 meters of the shelf bottom had been worn away which made Larsen B more buoyant and more likely to become unpinned. There are other processes but essentially the water under the shelf is warmer, the shelf thins, rises and detaches.

There is a full understanding of the collapse mechanisms. Linked below is a peer reviewed paper that examines the Wilkins Ice Shelf. This paper was published the year before the collapse in 2009.
http://www.the-cryosphere-discuss.net/2/341/2008/tcd-2-341-2008.pdf

Now that I have been able to read the paper you cite above and some associated citations, it is very clear that you are correct to say that:

"It's not useful to conflate climate issues related to floating ice shelves at sea level in Antarctica with glacial climate issues at an average altitude of 7000 feet".

While at the same moment I have no option but to disagree with your final statement:

"There is a full understanding of the collapse mechanisms."

Yes, it is fair to say that there does seem to be a good understanding of the mechanisms involving Basal Melting caused by warm Ocean water underneath a floating ice shelf; yet even here there is disturbing evidence of crossed wires. Let me give you an example.

In the abstract of your cited paper: Changes of Wilkins Ice Shelf over the past 15 years and inferences on its stability, one reads: "We show that drainage of melt ponds into crevasses were of no relevance for the break-up at Wilkins Ice Shelf" (page 342 12 -14).

And yet in the associated citation: Rott, H., Rack, 5 W., Skvarca, P., and Angelis, H. D.: Northern Larsen Ice Shelf, Antarctica:further retreat after collapse, Ann. Glaciol., 34, 277–282, 2002. we read:

"Long melt seasons and the existence of melt water are argued to be one main factors to cause the disintegration of ice shelves”

Again, returing to Changes of Wilkins Ice Shelf; page 344 line 5: "Rising air temperatures and increased surface melting have frequently been considered as triggering parameters for ice shelf break-up and disintegration, although structural discontinuities and rheological criteria are also discussed (e.g. Glasser and Scambos, 2008; Vieli et al., 2007).”

Yes I do understand that the latter is later refuted by discussion that the dominant mechanism is failure zones caused by basal melting.

To return to my original point; firstly that it is my contention that there is a wealth of evidence that when events involving ice occur; they do so very rapidly. There are repeated examples within your cited paper. Changes of Wilkins Ice Shelf, eg: page 346 line 20, page 359 line 14, page 360 line 14, cascade failures, page 361 line 21 are good examples.

Secondly, where surface melt water accumilations occur on a surface at between 7,000 feet and 10,000 feet above sea level, they are an entirely different animal with major implications for the dynamics of the underlying ice, largely caused by a combination of; the kinetic energy of any subsequent water movement down through the ice mass and another seemingly unrecognised aspect; the adiabatic lapse rate within an air mass where the upper surface temperature, (at 10,500 feet), is above freezing, this last year, + 4.5 Degrees; means that the underlying column of air mass within the many channels caused by Moulins must be imparting additional heating to the underlying ice. The lapse rate being a reduction of temperature ~3 degrees per 1,000 feet rising from the surface; must also relate in the opposite direction when the surface temperature is above freezing.

I recently knocked out this short paper to describe my thinking.

A short note to add some new thinking to the energy inputs influencing the formation of the Peterman Glacier Ice Tongue

During the Greenland Ice Sheet melting season of roughly 30 days a very large proportion of the 1.7KM3 of upper surface melt water flows down from the surface to the glacier base via Moulins. The Peterman Glacier drains 6% of the total ice sheet. The ice sheet is up to 3,000m thick but for this debate I am assuming the maximum height of the Moulins is 2,000m AMSL

During the melt season, there will be a flow of melt water, from Moulins into the Peterman Glacier of 39,352 Litres per second from a hydraulic head of 2,000m which gives an energy input of 770MW/s or 2.78TW/hr. An ice melt flow of this magnitude will create a massive exit plume under the glacier at the grounding line and will add to the energy input eroding the glacier. I present an illustrated description of the likely result and discuss some of the further implications.

[charliebrown]

Re: Polar Ice: Crushed or Cubed

Thank you, i always highly regard your opinion. I think you are a "truth" seeker like me.
do you have the other end of this graph from 1880, to 1950. If we draw a regression line through this data set, a change in slope from 1950 - 2010 would be a very
strong indicator that agw is occuring. How does peak oil play into this? If oil does go to 200 to 300 a barrel, oil consunsumption would go down a lot.


Also a hat tip to santfe post #19. very nice arguments.

[lektrode]

Re: Polar Ice: Crushed or Cubed

Thank you, i always highly regard your opinion. I think you are a "truth" seeker like me.

+1 on dcarrigg
one of the more trusted/respected sources/opinions here, IMHO.
(and not just cuz he's an ole yankee with salt in his veins ;)

[Polish_Silver]

AGW and polar ice

Thank you, i always highly regard your opinion. I think you are a "truth" seeker like me.
do you have the other end of this graph from 1880, to 1950. If we draw a regression line through this data set, a change in slope from 1950 - 2010 would be a very
strong indicator that agw is occuring. How does peak oil play into this? If oil does go to 200 to 300 a barrel, oil consunsumption would go down a lot.


Also a hat tip to santfe post #19. very nice arguments.

A regression line would not show what the cause is. It might be some indication if the slope had been very constant prior to that period, then suddenly changed, which I doubt.

There are always several possible causes for something like this. If AGW is the cause, wouldn't we expect equal melting in Antarctica? This is not observed. The earth is always warming or cooling. If it had cooled by 0.8C in the last 100 years, would that be a crisis?

Recent article by Christy challenging some ideas of AGW.

[charliebrown]

Re: AGW and polar ice

agreed, on the regression does not indicate cause. It would be suspicious if the slope of the line changed when fossil fuel use ballooned. i think i am beating a dead horse and all of this has already been hashed out. What about the heat island effect of recording stations?

Once again concern, but I don't want .gov taking control of our energy supplies more than they already to.

[santafe2]

Re: AGW and polar ice

If AGW is the cause, wouldn't we expect equal melting in Antarctica? This is not observed.

If we start from the premis that the Arctic and Antarctia are equal it may be more difficult to understand how differently they will handle a changing climate. The arctic is a place with some land but mostly it's a place with very cold water and a lot of sea ice over that water. Antarctica is not just a location, it's the 5th largest continent, larger than Europe and about twice as large as Australia. There are other reasons the Arctic will warm more quickly but if we only understand this difference we begin to understand how much more slowly Antarctica will change.

[santafe2]

Re: AGW and polar ice

What about the heat island effect of recording stations?

You may find this interesting. Scientists / organizations from around the world have deployed ~3,000 robotic probes in the ocean. The deployment has been complete for about 5 years but data sets are still too recent to project trends. I suspect we'll gain a solid understanding from the ARGO deployment.

http://en.wikipedia.org/wiki/Argo_(oceanography)

[santafe2]

Re: Polar Ice: Crushed or Cubed

Thank you for the reply. For myself I can never know the answer to the question, is the temperature increase or decrease, part of the evolution of the planet.

Given these sorts of questions I find it useful to perform very basic thought experiments. For example, what would the earth be like if C02 were at 1000PPM? If we think 1000PPM would create an unacceptable environment, we then should decide where an acceptable upper limit may be. Simple. If 1000 is too high, what is not too high. From there we can discuss the science until we come to a place where the majority of us agree. After that, we can do the same with policy.

In 1979 well before climate change was a political and social issue, a very smart scientist named Jule Charney lead an interdisciplinary team on a similar thought experiment. Assume CO2 doubled overnight, how much would temperature change? It's worth reading.
http://www.atmos.ucla.edu/~brianpm/d...ney_report.pdf

[Chris Coles]

Re: AGW and polar ice

If we start from the premis that the Arctic and Antarctia are equal it may be more difficult to understand how differently they will handle a changing climate. The arctic is a place with some land but mostly it's a place with very cold water and a lot of sea ice over that water. Antarctica is not just a location, it's the 5th largest continent, larger than Europe and about twice as large as Australia. There are other reasons the Arctic will warm more quickly but if we only understand this difference we begin to understand how much more slowly Antarctica will change.

This from NASA Earth Observatory

"Some of the most dramatic changes in recent years have occurred at Hektoria and Green glaciers, tributaries on the northern edge of Larsen B drainage basin. Between 2002 and 2006, the two glaciers lost an average of 4.2 gigatons of ice per year; between 2006 and 2011, they lost 5.6 gigatons per year. In their lower reaches, the two glaciers have lost about 220 meters (720 feet) of vertical thickness since 2002"

http://earthobservatory.nasa.gov/IOTD/view.php?id=79493

[Polish_Silver]

christy on heat islands

What about the heat island effect of recording stations?

Christy gets into this in an interesting way. Most of the warming is due to warmer nights. Daytime temps have not changed much. If it is greenhouse warming, both day and night should have changed equally. Christy says the warmer nights could be caused by human land use changes---more pavement, more buildings, etc, which cause more mixing of the atmospheric layers.