139 replies to this topic

[loafer]

What, other than a Gigaton sounds like alot, and 0.00003% doesn't?!

No wonder there are climate sceptics.

Science needs objectivity.

[Devonian]

loafer, on 27 December 2011 - 22:26 , said:

What, other than a Gigaton sounds like alot, and 0.00003% doesn't?!

No wonder there are climate sceptics.

Science needs objectivity.

But, isn't the NASA Giga tonne figure for the peninsula and your % for the whole Antarctic?

I accept, and I'm sure NASA would, that not much of the total ice of Antarctica has been lost but it's also beyond dispute that a lot of ice has been lost form the peninsula - which, again, was what the article was about?

What % of Antarctic peninsula ice has been lost?

[loafer]

If you want to make it sound like a big figure, make it a %age of part of the peninsula...

Why don't you tell me what percentage of the peninsula ice it is...or don't they release that data because it doesn't sound so impressive...?

Science. Data matters.

[Devonian]

loafer, on 27 December 2011 - 23:08 , said:

If you want to make it sound like a big figure, make it a %age of part of the peninsula...

Why don't you tell me what percentage of the peninsula ice it is...or don't they release that data because it doesn't sound so impressive...?

Science. Data matters.

But the article was about the Antarctic peninsula.

If I wrote an article about ice loss in the Antarctic peninsula I'd no more show that as a % of total Antarctic ice than I would show UK unemployment as a % of the total European workforce in an article about UK employment.

Edited by Devonian, 27 December 2011 - 23:14 .

[loafer]

I understand what you are trying to say, but it's premise is biased from two perspectives;

Firstly, I presume they didn't study other areas where ice wasn't breaking off.
Secondly, they didn't provide any context for their weight measurement within the study area so we don't know whether it is a little or alot? You and GW seem to have got excited by the word Gigaton without context.

I do agree that the weight over a subset study area, so dividing by the whole volume is equally misleading, but in the absence of any other objective context, we have no choice and at least it shows how minor the ice loss is in the context of the wider Antarctic.

What is certain is that it is pointless basing additional doom-laden questions speculating about the tipping point of the Antarctic shelf based on incomplete data - perhaps you can find the contextual info so we can work out whether we need to panic, or whether it is a PR release bolstering a fund raising, or somewhere between?

[Boar Wrinklestorm]

Devonian, on 27 December 2011 - 20:13 , said:

But we don't know if that loss is: like saying losing part of your brain is only a tiny part of your body, or like losing a toe, or indeed like taking a crucial piece out of a Jenga tower? And, since much of the ice lost in in the small area of the Antarctic Peninsula the % loss there is much larger? Of course Antarctica is a continent surrounded by water, it's also, mostly, very high. Much of it can stand a fair bit of warming with little change? But, is it like a toe, a brain or a Jenga block? Do we know?

Nature, it seems to me, is much more resilient than most of us would dare give her credit for.

Consider an analogue for the human neuron (since you mentioned the brain),



Here, we have two inputs, x, that are fed into a neuron, u. That neuron produces an output, y. The inputs are weighted, w, and the neuron only fires - is activated - (outputs to y) when sufficient input, u has been received. The picture, I'm sure, speaks better than a thousand of my words. For completeness, here's the maths,



Let's try a test run. First we need to assign some weights to our system for the inputs. We shall say w₁=0, and w₂=1. We also need to set an activation level for the neuron which we'll set at 0.5. There is now enough to perform a couple of experiments with our (very) mini-brain. Consider the following,



Here, we calculate u by the sum u = (x₁ * w₁) + (x₂ * w₁), and we have the cases for all classes of input where x₁ and x₂ can either be zero or one. So, for instance, picking case three (x₁=1,x₂=0) we plug in the values to our sum u=(1*0)+(0*1)=0, which is not enough to exceed our threshold, 0.5, so y stays as zero.

Now's where things get a little interesting. What if the connections to the neuron (modelled here by the weights) get corrupted somehow? ie there's some damage to the system? Well, let's try it: we'll set the weights to be w₁=0.2, and w₂=0.8. Here's the results,



Note that the internals have changed but the results are identical (if you're really interested, it's fairly routine to stick this in a spreadsheet and compute the values) Let's concede that it could be the inputs, not the weights changing. Here's the results,



Still the same results. An interested reader could easily dream up values that catastrophically change the output values of the system, but that's not the point. This is a classic example of non-linear dynamics. In linear systems, the inputs and outputs are related, so that outputs are always proportional to the inputs. Here, this non-linear system, we can see we can change the inputs -slightly, perhaps - without any behavioural changes in the outputs.

We can say that the system is robust to failure - ie we can change the system beyond all recognition and it still functions, perfectly,



We can, however, make enough changes of enough magnitude so that the system collapses, catastrophically,



We do not know at what point the Earth's climate (a non-linear system) will collapse catastrophically. We know when the sun enlarges to be a red-giant, that it's pretty much toast, but on a closer level, we cannot tell. There is, however, some evidence that points to such collapses (colloquially, tipping points) and the consequences, therein Consider the Vostok ice-core data,



A familiar chart for all those interested in climate, I'm sure. An overwhelming characteristic of this chart is the near sinusoidal (!!) pattern of the planet heating up, more or less in conjunction with CO₂, and then a catastrophic collapse of temperatures once the planet hits more or less the same temperature. This pattern strongly implies a maxiumum temperature limit of the Earth with a massive collapse in some feedback or another, plunging the planet into a much more dangerous period than that of ~2C warming. We can infer that once we get to somewhere between +2C to +3C we'll know for sure - possibly in our lifetime.

My apologies for the verbosity of this post. The aim is to get people to understand that climate dynamics are much resilient than most realise, and that catastrophic failure, actually, is very difficult to achieve in such non-linear systems.

Most of the neural network stuff is derived from here

Edited by Boar Wrinklestorm, 28 December 2011 - 11:12 .

[songster]

The point about ice shelves is not that they are a significant part of sea ice area: they are not. Nor indeed are they a significant part of the ice cap area or volume - the peninsula is something like 1-2% the size of the continent, which would upgrade that 0.00003% figure (percentage of Antarctic ice volume) to ~0.0015% (percentage of peninsula ice volume), depending on the relative thicknesses of the ice sheet in each area. Even if I'm out by an order of magnitude there, it's still an irrelevant percentage.

However, ice shelves constitute the restraining dam that slows down the glaciers dumping ice into the ocean. Consider the Hoover dam. It is about 0.0075% of the volume of Lake Mead, which is strikingly similar to the ice sheet percentage. We can't therefore assume it's safe for even a small proportion of the Hoover dam to crumble. Conversely, if it were to start crumbling, until and unless the lake itself starts to drain, the concrete rubble coming from the dam would have no measurable effect on the surface area of the Colorado River, or indeed the level of the Pacific ocean.

Edited by songster, 28 December 2011 - 11:44 .

[loafer]

Thanks both - very interesting.

[Devonian]

Boar Wrinklestorm, on 28 December 2011 - 11:01 , said:

Nature, it seems to me, is much more resilient than most of us would dare give her credit for.

...

We do not know at what point the Earth's climate (a non-linear system) will collapse catastrophically. We know when the sun enlarges to be a red-giant, that it's pretty much toast, but on a closer level, we cannot tell. There is, however, some evidence that points to such collapses (colloquially, tipping points) and the consequences, therein Consider the Vostok ice-core data,

...

A familiar chart for all those interested in climate, I'm sure. An overwhelming characteristic of this chart is the near sinusoidal (!!) pattern of the planet heating up, more or less in conjunction with CO₂, and then a catastrophic collapse of temperatures once the planet hits more or less the same temperature. This pattern strongly implies a maxiumum temperature limit of the Earth with a massive collapse in some feedback or another, plunging the planet into a much more dangerous period than that of ~2C warming. We can infer that once we get to somewhere between +2C to +3C we'll know for sure - possibly in our lifetime.

My apologies for the verbosity of this post. The aim is to get people to understand that climate dynamics are much resilient than most realise, and that catastrophic failure, actually, is very difficult to achieve in such non-linear systems.

Most of the neural network stuff is derived from here

I think a lot of this is right.

We don't know if the climate will 'collapse'. I doubt it will, but we/I don't know either way. I'm also of a 2-3C warming pursuasion (well, I'd go 2-4C so it's close). Though I do think warming of that level in a century pretty considerable.

In fact I do think more and more that the planet has seen changes of the magnitude we might cause, but that a change like we are causing over such an absolute instant of geological or planet time is not something Earth often has to deal with. Edit: so the earth might not behave as 'normal' as per your Vostok graph.

I expect to age, slowly over time, i don't expect to age fifty years in a day. I can cope with ageing normally, with the rate of change, with disease, but something so sudden and extrordinary would be all bets of in terms of effect on me.

I just think, have for decades, we're better not to carry out this big experiment with Earth. But, I'm stuck with us doing it....

Edited by Devonian, 28 December 2011 - 13:58 .

[Gray-Wolf]

If the folk who study the Arctic/Antarctic are correct then if the planet were to shed it's ice it would be quite happy to plod along without it. In other words the level of icing we have helps keep that ice. Remove the ice and the planet will settle to it's new point.

As such I feel that this area of 'climate science' has to accept a weighting in favour of de-glaciation (I'm not talking the loss of all of Antarctica or Greenland here but a certain amount of die back of the ice held there) and we appear to have 'pushed' ourselves in that direction far quicker than nature alone could have of achieved?


From my own point of view I can see that the ice shelfs in Antarctica will become redundant once we have lost this period of 'splendid isolation' that the ozone losses have helped place Antarctica in., The lessons that the peninsula (pushing out beyond the zone of splendid isolation) shows is that , once lost even the speed up of the glaciers behind does not replace the lost ice mass.

We have breached the Circumpolar current by trick of warm water flowing though 'canyons' on the sea bed and these waters are now nibbling at Pine Island Glacier. The one after that is the Ross Ice shelf and it's loss will unleash a fair amount of the E.A.I.S. drainage into the southern oceans. To me this will be the point of no return for the continent?

EDIT: Record temps at the south pole?

http://amrc.ssec.wis...arby-aws-sites/

Edited by Gray-Wolf, 29 December 2011 - 14:45 .

[loafer]

http://www.newscient...-is-stable.html

"A new model suggests that prehistoric sea-level rise long thought to have been caused by the ice sheet melting was actually the result of local subsidence."

"Global sea level could have been that high only if the East Antarctic ice sheet melted at the time, according to climate models. And that is odd: this ice sheet doesn't seem to have melted at any other point in its long history."

[songster]

To be fair, the Greenland and West Antarctic ice sheets did melt (or at lease shrink significantly) at that time, it's only the East Antarctic sheet that didn't. Losing any one of them would be bad news for us.

[Weather Ship]

West Antarctic Ice Shelves Tearing Apart at the Seams

A new study examining nearly 40 years of satellite imagery has revealed that the floating ice shelves of a critical portion of West Antarctica are steadily losing their grip on adjacent bay walls, potentially amplifying an already accelerating loss of ice to the sea.
The most extensive record yet of the evolution of the floating ice shelves in the eastern Amundsen Sea Embayment in West Antarctica shows that their margins, where they grip onto rocky bay walls or slower ice masses, are fracturing and retreating inland. As that grip continues to loosen, these already-thinning ice shelves will be even less able to hold back grounded ice upstream, according to glaciologists at The University of Texas at Austin’s Institute for Geophysics (UTIG).

http://www.jsg.utexas.edu/news/?p=3471

[Weather Ship]

Satellite observes rapid ice shelf disintegration in Antarctic

5 April 2012
As ESA’s Envisat satellite marks ten years in orbit, it continues to observe the rapid retreat of one of Antarctica’s ice shelves due to climate warming.

One of the satellite’s first observations following its launch on 1 March 2002 was of break-up of a main section of the Larsen B ice shelf in Antarctica – when 3200 sq km of ice disintegrated within a few days due to mechanical instabilities of the ice masses triggered by climate warming. Now, with ten years of observations using its Advanced Synthetic Aperture Radar (ASAR), Envisat has mapped an additional loss in Larsen B’s area of 1790 sq km over the past decade.

The Larsen Ice Shelf is a series of three shelves – A (the smallest), B and C (the largest) – that extend from north to south along the eastern side of the Antarctic Peninsula.
Larsen A disintegrated in January 1995. Larsen C so far has been stable in area, but satellite observations have shown thinning and an increasing duration of melt events in summer.
“Ice shelves are sensitive to atmospheric warming and to changes in ocean currents and temperatures,” said Prof. Helmut Rott from the University of Innsbruck.
“The northern Antarctic Peninsula has been subject to atmospheric warming of about 2.5°C over the last 50 years – a much stronger warming trend than on global average, causing retreat and disintegration of ice shelves.”
Larsen B decreased in area from 11512 sq km in early January 1995 to 6664 sq km in February 2002 due to several calving events. The disintegration in March 2002 left behind only 3463 sq km. Today, Envisat shows that only 1670 sq km remain.

http://www.esa.int/S...DWMEWF0H_0.html

[Gray-Wolf]

Antone heard any reports of a big chunk of P.I.G. floating off? I know we were treated to lots of images of the crack but I've since lost all my links (house move) so cannot access any images.

[Weather Ship]

Gray-Wolf, on 12 April 2012 - 19:58 , said:

Antone heard any reports of a big chunk of P.I.G. floating off? I know we were treated to lots of images of the crack but I've since lost all my links (house move) so cannot access any images.

The only one I know of GW. Don't know whether this helps.

http://www.dailymail...Antarctica.html

Edited by weather ship, 12 April 2012 - 21:50 .

[Weather Ship]

WASHINGTON -- Warm ocean currents attacking the underside of ice shelves are the dominant cause of recent ice loss from Antarctica, a new study using measurements from NASA's Ice, Cloud, and land Elevation Satellite (ICESat) revealed.

An international team of scientists used a combination of satellite measurements and models to differentiate between the two known causes of melting ice shelves: warm ocean currents thawing the underbelly of the floating extensions of ice sheets and warm air melting them from above. The finding, published today in the journal Nature, brings scientists a step closer to providing reliable projections of future sea level rise.

The researchers concluded that 20 of the 54 ice shelves studied are being melted by warm ocean currents. Most of these are in West Antarctica, where inland glaciers flowing down to the coast and feeding into these thinning ice shelves have accelerated, draining more ice into the sea and contributing to sea-level rise. This ocean-driven thinning is responsible for the most widespread and rapid ice losses in West Antarctica, and for the majority of Antarctic ice sheet loss during the study period.

http://www.nasa.gov/...s-ice-loss.html

[Weather Ship]

Scientists discover new site of potential instability in West Antarctic Ice Sheet

Using ice-penetrating radar instruments flown on aircraft, a team of scientists from the U.S. and U.K. have uncovered a previously unknown sub-glacial basin nearly the size of New Jersey beneath the West Antarctic Ice Sheet (WAIS) near the Weddell Sea. The location, shape and texture of the mile-deep basin suggest that this region of the ice sheet is at a greater risk of collapse than previously thought.
Team members at The University of Texas at Austin compared data about the newly discovered basin to data they previously collected from other parts of the WAIS that also appear highly vulnerable, including Pine Island Glacier and Thwaites Glacier. Although the amount of ice stored in the new basin is less than the ice stored in previously studied areas, it might be closer to a tipping point.

http://www.eurekaler...a-sdn050912.php

[Weather Ship]

News Story - New studies improve scientists understanding of the potential contribution of the Antarctic Ice Sheet to global sea level rise

Date: 10 May 2012
Three peer-reviewed papers in Nature and Nature Geoscience published in recent weeks report the work of science collaborations between British Antarctic Survey (BAS) and leading UK and international researchers. The findings are the result of an urgent push by the international scientific community to understand better the causes of ice loss from the Antarctic Ice Sheet and the contribution that this makes today, and in the future, to global sea level rise.

n the paper Antarctic ice sheet loss driven by basal melting of ice shelves by H.D Pritchard, S.R.M Ligtenberg, H.A Fricker, D.G Vaughan, M.R van den Broeke, L. Padman, published on 26 April in the journal Nature the authors report that warm ocean currents are the dominant cause of recent ice loss in Antarctica.
In a paper from colleagues at the Alfred Wegener Institute, who are partners in the EU-funded ice2sea programme led by British Antarctic Survey: Twenty-first-century warming of a large Antarctic ice shelf cavity by a redirected coastal current by Hartmut H. Hellmer, Frank Kauker, Ralph Timmermann, Jürgen Determann, Jamie Rae, published in Nature 10 May 2012. The authors describe their latest calculations for future sea-level rise and the relevance of this research for making policy and business decisions relating to sea defences around the world. For more information see the ice2sea website
In a letter to Nature Geoscience Published 10 May 2012: Steep reverse bed slope at the grounding line of the Weddell Sea sector in West Antarctica by Neil Ross, Robert Bingham, Hugh Corr, Fausto Ferraccioli, Tom Jordan, Anne le Brocq, David Rippin, Duncan Young, Donald Blankenship and Martin Siegert. The authors from British Antarctic Survey,the Universities of Edinburgh, Aberdeen, Exeter, York and from the University of Texas at Austin describe how they discovered a huge under-ice basin the size of Wales using radio-echo sounding technology. This discovery indicates that a larger area of the West Antarctic Ice Shelf is vulnerable to ice loss than previously thought.

http://www.antarctic...ory.php?id=1814

[paul tall]