Antarctic ice shelf half the size of Scotland on verge of collapse

[Count Iblis]

http://www.guardian.co.uk/world/2009/apr/05/ice-shelf-wilkins-antarctic"

A huge ice shelf in the Antarctic is in the last stages of collapse and could break up within days in the latest sign of how global warming is thought to be changing the face of the planet.

The enormous Wilkins ice shelf is now barely attached to land. The latest reports show that a thin sliver of ice attaching it to the Antarctic's Charcot Island is rapidly collapsing and threatening to break.

 

[Skyhunter]

Here is a video showing the Wilkins ice shelf

https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/poKX6OnehTc&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/poKX6OnehTc&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

 

[Xnn]

http://www.antarctica.ac.uk/press/press_releases/press_release.php?id=376

The breakout is the latest drama in a region of Antarctica that has experienced unprecedented warming over the last 50 years. Several ice shelves have retreated in the past 30 years - six of them collapsing completely (Prince Gustav Channel, Larsen Inlet, Larsen A, Larsen B, Wordie, Muller and the Jones Ice Shelf.)

Professor Vaughan continues,

"Climate warming in the Antarctic Peninsula has pushed the limit of viability for ice shelves further south – setting some of them that used to be stable on a course of retreat and eventual loss. The Wilkins breakout won't have any effect on sea-level because it is floating already, but it is another indication of the impact that climate change is having on the region."

JIM ELLIOT, BRITISH ANTARCTIC SURVEY:

The collapse of the 32502 Larsen B Ice Shelf took place in 2002. During the past 40 years the average summer temperatures in this region of the north-east Peninsula has been 2.2°C. The western Antarctic Peninsula has showed the biggest increase in temperatures (primarily in winter) observed anywhere on Earth over the past half-century.

The Antarctic Peninsula is an area of rapid climate change and has warmed faster than anywhere else in the Southern Hemisphere over the past half century. Climate records from the west coast of the Antarctic Peninsula show that temperatures in this region have risen by nearly 3°C during the last 50 years – several times the global average and only matched in Alaska.

There are about 1,500,000 km^2 of ice shelves in Antarctica.
Wilken is about 16,000 km^2 of that or about the size of Connecticut or Jamaica.

Good news is that when they breakup they do not contribute much to a rise in sea level. However, the rate of breakup is such that there won't be many left in another 100 years or so.

The Arctic used to have ice shelves too. However, they are mostly gone now. Once ice shelves are gone, the warming begins to work on land based ice and that melting does contribute directly to a rise in sea level. No need to immediately sell ocean front property, but long term this will be an issue.




http://news.bbc.co.uk/2/hi/science/nature/3132074.stm

Mueller, Vincent, and Jeffries say their calculations suggest changes of a similar nature have been taking place in the Ellesmere Island area.

A century ago, the entire northern coast of the island was reported to be fringed with a continuous ice shelf. About 90% of that ice area had been lost by 1982, the scientists say.

 

[Count Iblis]

An enormous amount of fresh water goes to waste. 16,000 km^2 and a thickness of 100 meters, that's about 1400 km^3 of water. People can live quite well with 100 liters per day, so this would be enough for the entire world for 6 years.

 

[Gokul43201]

The breakout is the latest drama in a region of Antarctica that has experienced unprecedented warming over the last 50 years.

Yet, we know that, on the whole, the Antarctic (and nearby SH) regions have, if anything, only been gaining ice coverage over the last few decades.

http://nsidc.org/data/seaice_index/

So then, are there other regions of the Antartic shelf that are experiencing unprecedented cooling? Or if not, is the region of warming small compared to the regions of cooling? And if that is the case, what makes this significant?

An enormous amount of fresh water goes to waste. 16,000 km^2 and a thickness of 100 meters, that's about 1400 km^3 of water. People can live quite well with 100 liters per day, so this would be enough for the entire world for 6 years.

Looks like the Antarctic gains more fresh water every year than it loses. I think if you're worried about losing fresh water, you would be better served looking at Arctic sea ice coverage (not that anyone is very likely to bankroll a start-up that chips off ice from Greenland and ships it to refugee camps in Rwanda).

 

[mgb_phys]

Yet, we know that, on the whole, the Antarctic (and nearby SH) regions have, if anything, only been gaining ice coverage over the last few decades.

That could make sense, warming oceans = more water vapour in the air = more precipitation.

 

[Xnn]

Gokul;

The most current peer reviewed paper on the subject has found that there is robust warming across Antactica:

significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica, an area of warming much larger than previously reported.

http://www.nature.com/nature/journal/v457/n7228/abs/nature07669.html

Sea ice comes from more than just freezing temperatures. With the breakup of such massive ice shelves, it's not too surprising that sea ice extent has trended upward. These ice shelves are initially hundred of meters thick. After they float out to sea, they eventually breakup into smaller pieces and then cover surface areas much larger than they did originally.

The Arctic on the other hand has almost no ice shelves left. This is why there is never any news about them and also why sea ice extent in the North has been trending downward. However, both polar regions are warming.

 

[Gokul43201]

That could make sense, warming oceans = more water vapour in the air = more precipitation.

But that's only part way through an explanation. You'd then have to connect precipitation to ice coverage, but more importantly, show that it is the dominant source of ice formation. And even then, this may be a bit of an oversimplification. After all, the Arctic has indeed been losing ice a lot more rapidly than the Antarctic has been gaining it. And that's been going on for at least a few decades now. But yes, I recognize that it could make sense (i.e., be reconciled by an argument based on even somewhat elementary principles, though I'm skeptical, because I think there are more factors involved such as wind patterns, ocean currents, deep water migration and other such complexities)... but that part of it was not really what I was questioning here.

Gokul;

The most current peer reviewed paper on the subject has found that there is robust warming across Antactica:

significant warming extends well beyond the Antarctic Peninsula to cover most of West Antarctica, an area of warming much larger than previously reported.

http://www.nature.com/nature/journal/v457/n7228/abs/nature07669.html

I haven't read the paper yet, but "most of West Antarctica" still sounds like less than half the continent.

Sea ice comes from more than just freezing temperatures. With the breakup of such massive ice shelves, it's not too surprising that sea ice extent has trended upward. These ice shelves are initially hundred of meters thick. After they float out to sea, they eventually breakup into smaller pieces and then cover surface areas much larger than they did originally.

The Arctic on the other hand has almost no ice shelves left. This is why there is never any news about them and also why sea ice extent in the North has been trending downward. However, both polar regions are warming.

I can't say I fundamentally understand this argument, but nevertheless, an explanation of this kind is essential to making some kind of logical connection between "global warming" and one particular ice shelf breaking up (and I didn't find any attempt at such an explanation in any of the articles posted) . After all, I think it is undisputed that warming over the SH is significantly weaker than over the NH. So when averaging over entire hemispheres give such an easily detectable divergence from the mean trend, I see very little usefulness in suggesting a correlation between the value of some chosen proxy integrated over such a small region as a particular section of Antarctica and a global trend. And I say "suggesting" because that is really all I see in the articles linked so far; there seems to be more innuendo and suggestion than any real attempt at explanation.

 

[sylas]

You'd then have to connect precipitation to ice coverage, but more importantly, show that it is the dominant source of ice formation. And even then, this may be a bit of an oversimplification. [...]

Um, what? I may be reading you wrong, but that looks a very odd comment.

Do you have other ideas for how an ice cap builds up? The whole basis of deuterium temperatures obtained in paleoclimate studies from ice cores is based on the fact that an ice cap is built up by precipitation.

Cheers -- Sylas

 

[mgb_phys]

But that's only part way through an explanation. You'd then have to connect precipitation to ice coverage, but more importantly, show that it is the dominant source of ice formation.

I just meant that "more snow != global warming is false"
I don't know if thse ice shelves are the result of recent local snow fall or they are ancient ice that moved in glaciers from further inland. Which would also mean the recent increase in ice coverage in the graph is irrelevant.

ps. why the size of Scotland? The standard unit for size is "Wales". And at 20,000km^2 is a lot closer to the size of this event than Scotland (at 75-80,000km^2) anyway

 

[Gokul43201]

Um, what? I may be reading you wrong, but that looks a very odd comment.

No, I think you read me right. But I didn't do a good job of saying what I meant. I guess I should have used a word like 'accumulation' rather than 'formation.' I may still be completely wrong here, since I know very little about this stuff, but nevertheless, I was trying to say that trends in ice coverage need not correlate very strongly with trends in precipitation.

Do you have other ideas for how an ice cap builds up? The whole basis of deuterium temperatures obtained in paleoclimate studies from ice cores is based on the fact that an ice cap is built up by precipitation.

This (like a lot of other things in this field) is something I didn't know about. But in any case, my intent was not simply on the rate of ice formation, but on the net rate of ice growth (formation rate - removal rate, I guess), since that is what shows up in the ice coverage trends.

 

[Gokul43201]

I just meant that "more snow != global warming is false

I hope I didn't give the impression that I was arguing that more snow => global warming is false. I was not making that argument. I was merely making the observation that given the overall ice coverage trends for the Antarctic, unprecedented loss of ice in some regions would seem to be more than made up for by significantly large gains of ice in other regions. More specifically, I was objecting to the suggestions that, in general, observations of unprecedented loss of ice in some small region X support the assertion that global warming is true.

 

[sylas]

No, I think you read me right. But I didn't do a good job of saying what I meant. I guess I should have used a word like 'accumulation' rather than 'formation.' I may still be completely wrong here, since I know very little about this stuff, but nevertheless, I was trying to say that trends in ice coverage need not correlate very strongly with trends in precipitation.

I'm at fault here for not following carefully.

The context of the remark, as I understand it, is from your [post=2149205]msg #5[/post], where you noted that there is increasing ice in the southern hemisphere. You were referring to sea ice cover; and I was thinking of the ice cap.

Yes, sea ice cover doesn't have much at all to do with precipitation. The biggest variations are, of course, between summer and winter, and relate to temperature. Differences from year to year are much smaller, and there are all kinds of effects that can have an impact on this. Ocean currents are important, especially around the Antarctic. I agree with you that changes in precipitation are unlikely to be much of a factor.

(Addendum added in edit: although it might. I'm reading a bit of background, and it seems that precipitation could be a factor after all.)

Cheers -- Sylas

 

[Xnn]

Here's an peer reviewed science journal article on increasing Antarctic sea ice. Although I'm not entirely comfortable with it, the suggestion is that decreasing salinity leads to a staginating ocean surface near that Antarctic. From this, less heat from the depths is available to melt the sea ice.

http://psc.apl.washington.edu/zhang/Pubs/Zhang_Antarctic_20-11-2515.pdf

The nature of the phenomenon of increasing Antarctic
sea ice in a warming environment may be explained
by the following (Fig. 10). When SAT/SDLR increases,
the upper-ocean temperature increases (which causes
SAT to increase concurrently through air–sea interactions)
and ice growth decreases, leading to a decrease in
salt rejection from the new ice and therefore in the
upper-ocean salinity. The increase in ocean temperature
and the decrease in ocean salinity result in a decrease
in water density in the upper ocean, leading, in
conjunction with reduced salt rejection, to enhanced
thermohaline stratification and weakened convective
overturning. Weakened overturning in turn reduces the
upward ocean heat transport, leading to reduced ocean
heat flux available to melt sea ice. The ocean heat flux–
induced ice melting decreases faster than the ice growth
in the weakly stratified Southern Ocean, which allows
for a large variation of the ocean heat flux, leading to an
increase in the net ice production and hence ice mass.
Thus, this study has identified a possible mechanism
that explains the increasing trend in Antarctic sea ice
under warming conditions. Note, however, that there
may be other mechanisms that can be used to explain
the paradox.