Polar Ice sets new minimum

[Stratos Ferric]

Interesting - I don't know very much about glaciers but I would have thought that they speed up when snow and ice from precipitation is added to their 'nursery' areas. If it was melting would it not just recede backwards? Also, how do they calculate these sea level rises is it a simple x tonnes of ice melts to create y litres of water or do they take into account the net because of the new ice/snow added to the glacier's catchment?

Glaciers don't speed up with more snow, they simply tend to grow, though even this is a simplification. A warmer climate MIGHT lead to more precipitation, but at the same time out of winter ablation and melt might increase at the snout, meaning the glacier might thicken but shorten. With continued warming the reductive forces would eventually win. If it's colder and wetter then the glacier will grow, though not speed up - the former can give the illusion of the latter, but it is just an illusion.

The main factor in glacial flow is not mass but friction and plasticity. In theory, a warmer glacier will be slightly more plastic, but the main factor is meltwater at the interface with the earth's surface. Pressure alone always ensures some water, but with a warmer climate there will be more percolated meltwater and as a consequence flows should be expected to increase.

[wysiwyg]

Thanks SF - I've certainly learnt quite a bit since I started looking into this since Sunday Morning!

I think the uniqueness of the PIG is that the apparent acceleration is being attributed to the snout's interaction with anomolously warm oceans. The potential this has to effectively 'float' a huge mass of ice that currently rests on the sea bed is mind-boggling and a little worrying.

I still can't help asking the question though that if large quantities of ice are falling into the sea then would not there be an element of negative feedback here i.e. warm water breaks off chunks of ice which melt (consuming a fair bit of latent energy during the phase change) reducing the ability of the sea to interact with the glacier's edge? Also would not phenomena such as La Nina/El Nino have a bearing on this - cold water pooled in the eastern Pacific leading to warm anomolies in the antarctic ocean. (reverse effect during El Nino)

These are not meant to be arguments against just an attempt to get a better understanding of what is happening.

Wysi

[Gray-Wolf]

try plopping a few ice cubes in your warm bath and see what impact you have! My concern is the 'flushing' of mega amounts of meltwater, currently stored under the EAIS, out and along the ocean floor causing displacement of the cooler waters leading to surface cold upwelling. Though not as pronounced this year we do seem to see a season flow of cold waters out of Mcmurdo sound and into the southern oceans popping up where it meets shelfs/islands leading to surface cold anoms. The overturning of the last El Nino and the implementation of the current La Nina coincided with such an event and was not as well predicted as it might have been (IMO)

[BLAST FROM THE PAST]

The overturning of the last El Nino and the implementation of the current La Nina coincided with such an event and was not as well predicted as it might have been (IMO)

Perfectly and very accurately forecasted/predicted by Theodore Landscheidt....and he died a few years back. In complete synchronisation with the solar cycle, this one is called the perturbation cycle.

BFTP

[wysiwyg]

try plopping a few ice cubes in your warm bath and see what impact you have!

OK shall I also salinate the water, cool it to -0.6deg C and chill the air in the bathroom to -40degC ?

Also if I put enough ice in the bath to raise it's level significantly I would expect to see some cooling certainly in a transient way close to where the ice was floating. Furthermore, if I put a large block of ice at one end that was resting on the bottom I would expect to see significant cooling even with repeated topping up with warm water. Hardly a representitive experiment methinks.

Also the cold fresh water is trapped under the ice sheet because it remains liquid due to the huge pressures underneath the ice. In other words it is supercooled liquid. So yes it would have a very significant effect on sea temperatures if it escaped.

Wysi

[biffvernon]

Hmmm, have a look at an atlas. Notice how big the PIG is and how big the Southern Ocean is. I think you'll find Gray-Wolf's analogy a bit more appropriate.

[wysiwyg]

Hmmm, have a look at an atlas. Notice how big the PIG is and how big the Southern Ocean is. I think you'll find Gray-Wolf's analogy a bit more appropriate.

Well now you are in danger of defeating your own argument - either this ice sheet causes significant sea-level changes or it doesn't. GW analogy may be appropriate on scale alone but not in terms of science given that the southern ocean isn't like a bath!

[Stratos Ferric]

OK shall I also salinate the water, cool it to -0.6deg C and chill the air in the bathroom to -40degC ?

Also if I put enough ice in the bath to raise it's level significantly I would expect to see some cooling certainly in a transient way close to where the ice was floating. Furthermore, if I put a large block of ice at one end that was resting on the bottom I would expect to see significant cooling even with repeated topping up with warm water. Hardly a representitive experiment methinks.

Also the cold fresh water is trapped under the ice sheet because it remains liquid due to the huge pressures underneath the ice. In other words it is supercooled liquid. So yes it would have a very significant effect on sea temperatures if it escaped.

Wysi

wysiwgy, be assured that the fresh water is anything but trapped. Streams run under all glaciers: without them the flow would be very slow indeed, and they are hugely pressurised. It is these streams that deposit sediment immediately at the the snout of a glacier, causing eskers (sinuous embankments) as the glacier or ice sheet retreats.

To your previous point. You're correct that any melt would interact with the ocean around the snout, but the cold water will naturally sink: warmer current, perhaps causing melt, will be closer to the surface. Perversely there might actually be an argument that once ice is introduced at the surface the local flow in the ocean might actually be accelerated, in the same way that the draw on my stove increases as the differential between the temperature in the stove and the chimney above increases.

The ocean is so much more massive than any glacier or ice sheet that the energy will continue to flux.

[I can't believe it's not better]

A heat engine !

[biffvernon]

Well now you are in danger of defeating your own argument - either this ice sheet causes significant sea-level changes or it doesn't.

25 cm may not be very significant in relation to the depth and volume of the oceans but it can make all the difference to millions of lives in the face of a Bay of Bengal cyclone.

[biffvernon]

Scientists from British Antarctic Survey (BAS), Durham University and Germany’s Alfred Wegener Institute for Polar and Marine Research (AWI) collected boulders deposited by three glaciers in the Amundsen Sea Embayment – a region currently the focus of intense international scientific attention because it is changing faster than anywhere else on the WAIS and it has the potential to raise sea-level by around 1.5 metres.

Analysis of the boulders has enabled the scientists to start constructing a long-term picture of glacier behaviour in the region. An urgent task is to put recent ice sheet changes into a historical context, and determine if these are part of a natural retreat since the end of the last glacial period (about 20 thousands years ago), or if they are a result of recent human-induced climate change.

Lead author Dr Joanne Johnson of BAS says,

“Until now we didn’t know much about the long-term history of this part of the West Antarctic Ice Sheet because the region is incredibly remote and inaccessible. Our geological findings add a new piece to the jigsaw and will be used for improving computer models – the most important tools we have for predicting future change.”

Initial results show that Pine Island Glacier has ‘thinned’ by around 4 centimetres per year over the past 5,000 years, while Smith and Pope Glaciers thinned by just over 2 cm per year during the past 14,500 years. These rates are more than 20 times slower than recent changes: satellite, airborne and ground based observations made since the 1990s show that Pine Island Glacier has thinned by around 1.6 metres per year in recent years.

more at BAS

[NorthernRab]

The melting of such a massive stretch of ice would cause warming due to the white reflective ice being replaced by dark blue sea, would it not? Thus excelerating the melt of other glaciers elsewhere?

[biffvernon]

That's true for the Arctic sea ice, but in the Antarctic most of the ice rests on land and even if it did eventually slip into the sea it would still be a very cold snowy place even after a great deal of global warming. On the PIG, for example, the recent report we have been discussing mention summer temperatures of minus 30.

[NorthernRab]

Ah I see, but would it surely not still have something of an affect? I'm aware that Antarctica is itself an actual land-based continent (similiar idea to Greenland I suppose), but surely the loss of ice would still boost temperatures in warmer areas of the continent?

Edited March 3, 2008 by NorthernRab

[Gray-Wolf]

Ah I see, but would it surely not still have something of an affect? I'm aware that Antarctica is itself an actual land-based continent (similar idea to Greenland I suppose), but surely the loss of ice would still boost temperatures in warmer areas of the continent?

It would have a Major impact (as we are seeing on the peninsula area) with both higher temps and different weather. If you look at the vast area that is the Ross Ice shelf then you'll see just how much of Antarctica will suddenly be above freezing (but below sea level) when the shelf fails. See the fringing mountains to the rear of Ross? they already have snow melt over summer (over 1km up) so imagine what a 'warm' sea lapping at their feet would bring to the lower levels (as in the peninsula). Then take a peep at the Weddell sea and imagine it ice free 6 months a year and the impact on the east of the peninsula that would have also.

The EAIS is higher than Greenland so just the environmental lapse rate would lead to a chilly top before you bring in 24hr darkness. However a milder coast bring enhanced precipitation to the centre and more snow means more dynamic upper reaches of the glaciers that form/flow there.

Don't let them fool you into thinking Antarctica is apart from the rest of the planet, it's just wishful thinking as it poses the greatest threat to humanity.

[keithtod43]

It would have a Major impact (as we are seeing on the peninsula area) with both higher temps and different weather. If you look at the vast area that is the Ross Ice shelf then you'll see just how much of Antarctica will suddenly be above freezing (but below sea level) when the shelf fails. See the fringing mountains to the rear of Ross? they already have snow melt over summer (over 1km up) so imagine what a 'warm' sea lapping at their feet would bring to the lower levels (as in the peninsula). Then take a peep at the Weddell sea and imagine it ice free 6 months a year and the impact on the east of the peninsula that would have also.

The EAIS is higher than Greenland so just the environmental lapse rate would lead to a chilly top before you bring in 24hr darkness. However a milder coast bring enhanced precipitation to the centre and more snow means more dynamic upper reaches of the glaciers that form/flow there.

Don't let them fool you into thinking Antarctica is apart from the rest of the planet, it's just wishful thinking as it poses the greatest threat to humanity.I cannot allow you to print doom and gloom reports on the bbc the other day reported about the record amount of ice in the antartic and alot of South America (peru thousands die record cold temperatures,Brazil snow Argentina snow,)experienced severe winter. New Zealand records amount of cold weather.

[BUSHY]

dont panic - the freeze up down south has started early and is way above the mean.

[biffvernon]

That's an early call for panic over. Sources?

[BLAST FROM THE PAST]

dont panic - the freeze up down south has started early and is way above the mean.

Agreed and correct

BFTP

[Gray-Wolf]

After peaking at 2 msq km above the same time last year the ice min'ed out at 0.2 msq km above last year (and this a La-Nina year!)

If the info is from C.T. then a read at the top of the page will enlighten you to their current data 'problems'.

With most of the shelf areas now facing open waters the prospect of the first winter storms 'pnuematically piling' their interface with the land is at it's greatest. Until the sea ice reforms to a thickness that effectively 'damps out' the swell (like pouring oil on troubled waters) then this years land melt leaves the shelfs vulnerable.........for a few weeks yet!

[BUSHY]

GW if you doubt the facts pull up the corresponding graphics for the same period 2007/2008 and compare them. There are various sources not just CT. There is no difference to open water areas this year as compared to any other on balance.

[Gray-Wolf]

GW if you doubt the facts pull up the corresponding graphics for the same period 2007/2008 and compare them. There are various sources not just CT. There is no difference to open water areas this year as compared to any other on balance.

I heartily agree with you BUSHY, and for a year that purported to have an extra 2 million square kilometres of sea ice (produced at the time the ice should have been declining) to find us a mere 200,000 square km up is astonishing.

As you well note the 'season' has been just another of the recent 'cold years' down sarf' and certainly not the kind of year to produce the late season spurt of pack ice growth we were asked to believe back in Aug/Sept.

But then if the 'extra ice' was merely poorly mapped 'relaxed' pack then you could see it spreading out to cover that area..................

[biffvernon]

Best not to try to read too much into Antarctic sea ice extent. Unlike in the Arctic, it varies a lot from year to year, with precipitation being important.

Radio 4 Home Planet this afternoon had a discussion about the PIG

http://www.bbc.co.uk/radio4/science/homeplanet.shtml

[Gray-Wolf]

I couldn't agree more B. The real measure seems to be the continental output (shelf collapse, glacier output, precipitation) and changes within the ice sheet itself (sub ice lakes/rivers).

As Mr Gumbine made clear the ice extent is dependant upon a good 'mask' as a start point and he ,for one, had no idea as to how regular the updates are. With shelf ice in excess of the total area of the UK lost over the last 10yrs you have to wonder how 'up to date' the masks are if the head of the sea ice group from the US base at Mcmurdo neither know nor cares!

[BLAST FROM THE PAST]

So the antarctic is still gaining ice and not about to collapse then, good....didn't think so.

BFTP

Edited March 6, 2008 by BLAST FROM THE PAST