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werther

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Greenland ice sheet retreat
« on: January 17, 2015, 12:43:06 AM »


I have finally taken time to finish a comparison for the Greenland icesheet between 2009 and 2012.
I will produce a justification, but first let me expand on the result:

Greenland icesheet and snowcover extent comparison:
Year      contour/circumference      surface
2009      47967 km1         1.819.626 km2
2012      55308 km1         1.792.659 km2

Given these data, the surface retreat in three years was 26.967km2. This implies a mean contour retreat of about 560m1.

Justification

I selected the best MODIS tiles available for the second week of July 2009 and 2012. After fitting these in a CAD grid, I created a polyline representing the continuous ice-/snowline. Within the limits of resolution the polyline has about 3 vectorpoints per kilometre. Close to the 250x250m2 MODIS-pixel.
The complicated and difficult factor is a just and consistent allocation of these vectorpoints. I spent a lot of time on blurred parts of the MODIS images. On  the tour, I interpreted variable situations. Calved glaciers, occasional snow left after summer night precipitation, jokullhlaup debris fields looking like ice or snow but probably signifying broad sandrs where the precipitous meltwaters excited the glacier contours July 2012.

Maybe a consistent interpretation could be done through a program using set parameters. The weakness is that no parameter would be competent to judge different objects as they are represented on these MODIS images. No individual would reproduce the exact choices I made to set the polyline.  My endeavour may be vain. But you may find the result satisfying as an indication that it supports evidence of a consistent retreat of the GIS in line with for instance GRACE data.

To end this justification, I add that I left out any snow- or icefield not connected to the main Greenland ice sheet. Remaining fast ice has been cut out too. I’ll illustrate some details and interesting differences later.

For now, it seems right to indicate that some areas near Qaanaaq and the Steenstrup Glacier (NW GIS) gave the most difficulties for 2012 interpretation.
That doesn’t wipe out the general picture. There’s a consistent retreat of the snow- and ice contour, most obvious in the SE and South. It isn’t dramatic yet, but it is well in line with a pattern leading to a mean 4 km1 contour retreat producing about 3000 Gt of mass loss a year within a couple of years.

I did expect the process to advance smoother through the years. I didn’t foresee ’13 to be a minor melt year. Nevertheless, the extreme melt years to come will make up. In my opinion it will fit in a stage around 2050 where a large part of the southern tip of the GIS will have been severely reduced. That will equate to a global sea level rise of about 50 cm.

Sea level will rise in line with several stages of vulnerability on the large ice sheets around the globe. In my opinion, the Southern tip of Greenland is the most vulnerable.

On the map above, red is the simplified coastline, blue the overlying contour for 2009, the purple bits relate to the 2012 contour, that is obviously not dramatically different in July 2012 on this scale.


werther

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Re: Greenland ice sheet retreat
« Reply #1 on: January 17, 2015, 01:11:42 AM »
Illustrating the details 1.



Jokullhlaup?
Day 196 14 July 2012. Setting the polyline for the snow-/ice contour I stumbled upon this feature. About 140 km East of Maniitsoq, SE Greenland, a large swath of grey near the Sukkertoppen icefield.
The detail measures about 90x55 km2.
Set in a remote, uninhabitated part of the island, a sandr-debris flood occupying about 90 km2 could have passed unnoticed, although rivalling the Watson-bridge-demolish event in scope.
In this pic, the blue line accounts for the ’09 snow-/icecontour. The purple line stands for July ’12. I interpreted the Sukkertoppen icefield as severed from the main GIS continuous snow-/icesheet by that date.

Neven

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Re: Greenland ice sheet retreat
« Reply #2 on: January 17, 2015, 08:03:06 AM »
Very nice, Werther. Impressive.
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werther

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Re: Greenland ice sheet retreat
« Reply #3 on: January 19, 2015, 10:22:57 PM »
Detail 2: Southwest Greenland; the complicated glacier-cross near the Kangertittivatsiaq and Angmagssalik.



Blue is the ice-/snow contour July ’09. Purple for July ’12. The MODIS tile is used as a faded background for some orientation. The detail measures 50 x 50 km. The straight line is a MODIS-tile limit.

The comparison reveals consistent retreat of the contour. Upwards along slopes and into valleys. The joining glaciers in the middle have parted in July ’12. The snow- and icefree ground further up into the mainland is thus excluded from the continuous contour. Both effects result in lengthening the contour as the snow-/icesheet retreats, while the surface diminishes (see the data in the first post).

Considering the integral GIS:
the comparison reveals regional differences. Most glacierfronts have retreated, some seem steady, a handful has progressed. The snow contours in between have not retreated in some parts of the Southwest. Further to the NE the contour has even progressed in some parts. I’ll post a detail later.

Espen

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Re: Greenland ice sheet retreat
« Reply #4 on: January 20, 2015, 05:26:58 AM »
Midtgårdgletscher 1972 - 2013 retreat is described here:

https://forum.arctic-sea-ice.net/index.php/topic,559.msg14168.html#msg14168
« Last Edit: January 20, 2015, 05:37:34 AM by Espen »
Have a ice day!

werther

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Re: Greenland ice sheet retreat
« Reply #5 on: January 20, 2015, 10:16:50 AM »
Detail 3: Helheim glacier, southwest Greenland



One of the parts in southwest Greenland where the snow-/ice contour didn’t retreat much. Although the calving front on the Helheim Glacier is very mobile, there’s hardly a pixel-width difference between ’09 and ’12. In my opinion, the calving front is so close to the steep ‘bedrock’ slope into the mainland, that it can hardly retreat. Most of the floating tongue is already lost.
Nevertheless the feeding area keeps producing enough ice to let the glacier produce massive debris each year.

BTW thanks Espen. I love to get the topographic names right, but I sure appreciate some help here.

werther

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Re: Greenland ice sheet retreat
« Reply #6 on: January 21, 2015, 09:31:00 AM »
Detail 4: A.P. Bernstoff Glacier, SW Greenland



About 340 km to the South of Helheim Glacier A.P.Bernstoff Glacier is the main tributary on a 60 km deep fjord. Like Helheim, it has retreated close to the steep slope into the mainland. It’s calving front is very mobile, retreating or advancing depending on the dynamic flow out of the ice sheet.
July ’12 the fjord was filled with debris from the three calving glaciers on it’s head.

In this Southern part of the East coast the snow-/ice contour retreated back into each valley, creeping op on the slopes.

werther

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Re: Greenland ice sheet retreat
« Reply #7 on: January 21, 2015, 10:27:00 AM »
Detail 5: East Qorqup Glacier, South Greenland
The region East of Narsarssuaq; Qooroq- and Tunulliarfik Fjords

[/URL]

This part of Greenland shows the most retreat of the snow-/ice contour ’09 to ’12. To be expected, given the latitude (61 dg N, about as N as Far Oer or Bergen, Norge).
The MODIS tiles were not optimal, so I may have misinterpreted some properties on the sides of this large, fingered glacier. I excluded them from the ’12 polyline contour, because these sides seem to me to be in rapid disintegration. It wouldn’t surprise me if they had an almost ‘jokullhlaup-look’ on 13 July 2012.

Today I saw Mauri Pelto has a post on this glacier on his blog, 14 December ’14: https://glacierchange.wordpress.com/2014/12/14/east-qorqup-glacier-terminus-disintegration-greenland/

werther

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Re: Greenland ice sheet retreat
« Reply #8 on: January 21, 2015, 11:15:27 AM »
Detail 6: Inngia Isbrae, West Greenland
A 50 x 50 km2 region about 350 km N of Jakobshavn Isbrae/Sermeq Kujalleq.



Again a region of fierce retreat of the contour from ’09 to ’12. The floating glacier tip has retreated about 2.7 km1. Attachment to the Western snowfields has been lost. The smaller land-based glaciers North of the middle have lost contact. Snow cover is confined to elevations above 1700 m. All slopes show bare, rapidly melting, ice.

A feature 18 km to the East, to my regret outside this pic, is of interest. It is a 2 km2 wide melt pond right in line with the centered flow line of the glacier on 1200 m1 asl. I’ll have a look whether it’s character changes by July ’15.

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Re: Greenland ice sheet retreat
« Reply #9 on: December 09, 2016, 10:41:52 PM »
It appears Greenland 'goes away' far more often than we thought?

https://www.sciencedaily.com/releases/2016/12/161207133453.htm
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Pmt111500

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Re: Greenland ice sheet retreat
« Reply #10 on: December 11, 2016, 09:52:05 AM »
The paper in question is paywalled as is usual for these more extreme results (Add to the list of scientists the future government of US may want to sack) :

http://www.nature.com/nature/journal/v540/n7632/full/nature20146.html

(http://www.nature.com/nature/journal/v540/n7632/full/nature20146.html#affil-auth , it looks like there's one from a red state, and one from the military also)
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Re: Greenland ice sheet retreat
« Reply #11 on: December 13, 2016, 12:24:55 PM »
While relating to Antarctica, this report shows an 'interesting' way heat is penetrating ice shelves...

http://www.smh.com.au/environment/this-stunning-antarctic-lake-is-buried-in-ice-and-that-could-be-bad-news-20161212-gt9oco.html

I would imagine similar features could be found in Greenland, were researchers suitably funded to look.

Archimid

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Re: Greenland ice sheet retreat
« Reply #12 on: December 13, 2016, 01:29:19 PM »
It appears Greenland 'goes away' far more often than we thought?

If this is true, it changes everything. Global warming is ended by worldwide seismic activity and volcanism.

This is the sequence of events I imagine. Feel free to correct me.

1. The arctic sea ice goes, in less than a decade the Arctic ocean warms up.

2. Greenland melt accelerates, removing  gigatons of mass form greenland. Greenland rises.

3. This causes heat unnatural (for us) heat build up, seismic activity and eventual volcanism.

4. Volcanoes cool the atmosphere quickly, but the warm oceans keep melting Greenland (and Antarctica).

5. in 135k years, during the peak of an interglacial, a civilization forms. They wonder if climate change will be bad. They are absolutely sure they are at the peak of civilization and nothing can stop them. They never find evidence of our civilization.


If this is true there should be volcanic activity coinciding with past episodes of Greenland rapid melt.
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Tigertown

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Re: Greenland ice sheet retreat
« Reply #13 on: December 13, 2016, 02:16:00 PM »
The geothermal activity has been melting away at the ice there for a while now. I don't think all of the ice would have to melt to have major volcanic activity, because the land is already rising slowly, as the ice melts and the melt water drains to the ocean. Who knows when it will rise just the right amount to set things off.

Hefaistos

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Re: Greenland ice sheet retreat
« Reply #14 on: December 13, 2016, 03:08:39 PM »
Greenland is not known for any kind of volcanic activity.
It consists of some of the oldest (=stable) rocks on earth, as has been reported on this forum. I doubt that ice loss will trigger anything but earthquakes on Greenland.

https://blogs.nasa.gov/icebridge/2013/04/16/post_1366140794166/

Tigertown

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Re: Greenland ice sheet retreat
« Reply #15 on: December 13, 2016, 03:34:22 PM »
Saying that a place has geothermal activity is not saying it has currently active volcanoes.

https://news.umt.edu/2016/04/040616melt.php

Greenland has all the makings for a volcano. Not making a prediction, but saying it is possible, especially with the area of thin crust.

RoxTheGeologist

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Re: Greenland ice sheet retreat
« Reply #16 on: December 13, 2016, 06:09:36 PM »
Having volcanic rocks form over shields is pretty much unheard of. There is no evidence in any other region that has gone through rebound.

I would suggest you look at something like the Hoggar Massif, it has been uplifted by what is though to be mantle convection, and yet there is no active vulcanism. The uplift is on the order of KMs. Some domes do have active volcanoes, but only when there is Lithospheric stretching.

Partial melting happens when the solidus curve approaches the getothermal gradient. It can be in areas like mid ocean ridges or hotspots, where mantle upwelling shifts the geotherm, in subduction zones where, despite the cold ocean lithosphere, the solidus  is shifted by fluids. Continental accretion and stretching can also increase the proximity of the two to cause melt. Simply uplifting a block of lithosphere affects neither.
« Last Edit: December 14, 2016, 04:40:33 PM by RoxTheGeologist »

Tigertown

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Re: Greenland ice sheet retreat
« Reply #17 on: December 13, 2016, 08:48:33 PM »
What do you think you or a geologist or something, RoxTheGeologist?( oh, my bad)   ;)
Thanks for the clarification.

P.S. Look forward to anything else you might add to this subject.
« Last Edit: December 13, 2016, 09:00:40 PM by Tigertown »

Archimid

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Re: Greenland ice sheet retreat
« Reply #18 on: December 15, 2016, 02:34:39 PM »
Thank you to all that replied to my crazy thoughts. I think you miss understood. I do not mean volcanoes in Greenland. I mean that volcanoes and seismic activity all around the world will be affected by glacier rebound.

>Simply uplifting a block of lithosphere affects neither.

That statement is not true if the uplift is large enough, fast enough or the uplift is a tipping point. The way I see it the liquid mantle and asthenosphere have circulations like the oceans, even if they are unknown. Rapid deformation of the lithosphere might or might not change those circulations causing changes in volcanic and seismic activity.

Melting Greenland and Antarctica at an unnatural fast rate have a very high chance of disrupting subsurface circulations resulting in changes in volcanism. If eruptions are accelerated enough, then global cooling is a distinct possibility.
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RoxTheGeologist

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Re: Greenland ice sheet retreat
« Reply #19 on: December 15, 2016, 04:54:32 PM »
Thank you to all that replied to my crazy thoughts. I think you miss understood. I do not mean volcanoes in Greenland. I mean that volcanoes and seismic activity all around the world will be affected by glacier rebound.

>Simply uplifting a block of lithosphere affects neither.

That statement is not true if the uplift is large enough, fast enough or the uplift is a tipping point. The way I see it the liquid mantle and asthenosphere have circulations like the oceans, even if they are unknown. Rapid deformation of the lithosphere might or might not change those circulations causing changes in volcanic and seismic activity.

Melting Greenland and Antarctica at an unnatural fast rate have a very high chance of disrupting subsurface circulations resulting in changes in volcanism. If eruptions are accelerated enough, then global cooling is a distinct possibility.

The uplift rate is determined by viscosity of the asthenosphere. This is fairly well understood simply by studying raised beaches such as in Scotland. Scotland is still rebounding since the ice removal of the from the last ice age, and will continue for another 10000 years or so. Volcanism on the North American plate is seen only on the subduction boundary in the north west and over the Yellowstone hot spot, despite it continuing to rebound in the present day.

Seismic tomography has given us a pretty good idea of the mantel convection cells. Deformation of the lithosphere is the result of this convection. It doesn't drive it.

There is no evidence in the past of post glacial rebound causing melt.

Please don't confuse human time scales with geological time scales.


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Re: Greenland ice sheet retreat
« Reply #20 on: December 15, 2016, 06:24:20 PM »
Archimid


If Greenland melt is expected to promote volcanism, wouldn't the rapid loss of the Laurentide Ice Sheet have done so?


As I understand it the Canadian Shield has had very little volcanic activity.


Terry

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Re: Greenland ice sheet retreat
« Reply #21 on: December 15, 2016, 10:25:50 PM »

The uplift rate is determined by viscosity of the asthenosphere. This is fairly well understood simply by studying raised beaches such as in Scotland.


To that I would argue that the uplift rate is determined by the viscosity of the asthenosphere and the rate of change of mass at the surface.

Scotland is still rebounding since the ice removal of the from the last ice age, and will continue for another 10000 years or so.


My thinking is that at the during those times, volcanism probably increased, but the increase was spread out over thousand of years following the nice slow ice melt of the natural cycle. I'm sure that it will continue for thousands of years. But I bet  that the rate was higher during the fastest ice melt and after the low hanging fruit of volcanic activity was triggered, the rest of the process is slow by human time scales.

There is no evidence in the past of post glacial rebound causing melt.


I'm sorry but I have read otherwise:

http://www.cam.ac.uk/research/news/increase-in-volcanic-eruptions-at-the-end-of-the-ice-age-caused-by-melting-ice-caps-and-glacial

https://dash.harvard.edu/bitstream/handle/1/3659701/Huybers_FeedbackDeglaciation.pdf?sequence=1

>Please don't confuse human time scales with geological time scales.

I am not. Volcanism and ice melt is linked, but they both worked at geologic time scales.

Right now we have raised CO2 levels in 100 years to levels it takes earth 100k years. We are warming the planet at a rate that is not matched anywhere in the record. The arctics is being lost in a matter of decades.

We have caused events that used to happen over geological time in a century. If Greenland melts as unnaturally fast as we are warming the earth, then the seismic and volcanic activity as a result of the redistribution of water mass around the earth will very likely be unnaturally fast.
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

RoxTheGeologist

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Re: Greenland ice sheet retreat
« Reply #22 on: December 15, 2016, 11:28:04 PM »

The uplift rate is determined by viscosity of the asthenosphere. This is fairly well understood simply by studying raised beaches such as in Scotland.


To that I would argue that the uplift rate is determined by the viscosity of the asthenosphere and the rate of change of mass at the surface.

Scotland is still rebounding since the ice removal of the from the last ice age, and will continue for another 10000 years or so.


My thinking is that at the during those times, volcanism probably increased, but the increase was spread out over thousand of years following the nice slow ice melt of the natural cycle. I'm sure that it will continue for thousands of years. But I bet  that the rate was higher during the fastest ice melt and after the low hanging fruit of volcanic activity was triggered, the rest of the process is slow by human time scales.

There is no evidence in the past of post glacial rebound causing melt.


I'm sorry but I have read otherwise:

http://www.cam.ac.uk/research/news/increase-in-volcanic-eruptions-at-the-end-of-the-ice-age-caused-by-melting-ice-caps-and-glacial

https://dash.harvard.edu/bitstream/handle/1/3659701/Huybers_FeedbackDeglaciation.pdf?sequence=1

>Please don't confuse human time scales with geological time scales.

I am not. Volcanism and ice melt is linked, but they both worked at geologic time scales.

Right now we have raised CO2 levels in 100 years to levels it takes earth 100k years. We are warming the planet at a rate that is not matched anywhere in the record. The arctics is being lost in a matter of decades.

We have caused events that used to happen over geological time in a century. If Greenland melts as unnaturally fast as we are warming the earth, then the seismic and volcanic activity as a result of the redistribution of water mass around the earth will very likely be unnaturally fast.


Ah yeah, I didn't consider the possibility of changing pressure on a already existing melt area in a region on active volcanoes. That does make sense. Unlikely to happen in Greenland as there are no active volcanoes. It's not a mechanism that can generate partial melting.

Stephen

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Re: Greenland ice sheet retreat
« Reply #23 on: December 24, 2016, 03:39:21 AM »
It appears Greenland 'goes away' far more often than we thought?

If this is true, it changes everything. Global warming is ended by worldwide seismic activity and volcanism.

This is the sequence of events I imagine. Feel free to correct me.
.......snip....snip....
5. in 135k years, during the peak of an interglacial, a civilization forms. They wonder if climate change will be bad. They are absolutely sure they are at the peak of civilization and nothing can stop them. They never find evidence of our civilization.

.....

I am pretty sure that they will find evidence of the 450 or so nuclear power stations around the world.  I mean, the half life of plutonium is 250,000 years isn't it?  Assuming that this advanced civilization had invented the Muller-Geiger counter.  (poor old Muller never gets the credit he deserves).

Totally off-topic, but the wife and I watch "The Walking Dead" - a TV series about a post-zombie-apocalypse world.  I always tell her that the people have more to fear from the 60 (in the USA) now-unattended nuclear power stations turning into 60 Chernobyls or 60 Fukushimas than they do from the zombies.  She always tells me to shut-up.
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Avalonian

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Re: Greenland ice sheet retreat
« Reply #24 on: December 24, 2016, 05:01:22 AM »
If Greenland melt is expected to promote volcanism, wouldn't the rapid loss of the Laurentide Ice Sheet have done so?

As I understand it the Canadian Shield has had very little volcanic activity.

Melting of glaciers does indeed increase the chance of eruption, by reducing the containing pressure. This is seen very clearly in Iceland, where the summer melt produces large numbers of small volcanism-related earthquake swarms, and a higher incidence of eruptions... but it's statistical. Reducing the containing pressure increases the chance that an active volcano will erupt, but it doesn't dictate it. Volcanoes have their own agendas.

The Canadian Shield has little volcanic activity... because it's a shield. There are no volcanoes there to encourage, and you're certainly not going to get Bardabungas popping into existence when you take the ice off. If there had been volcanic feeder systems and shallow magma chambers present, though... then remove a few miles of ice and you're talking about quite some incentive to blow its top. 

Archimid

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Re: Greenland ice sheet retreat
« Reply #25 on: December 24, 2016, 02:36:15 PM »
I am pretty sure that they will find evidence of the 450 or so nuclear power stations around the world.  I mean, the half life of plutonium is 250,000 years isn't it?

Most of those plants will be ground to dust by glaciation and then drained to the oceans once the glaciers melt. I imagine they would find places with unusual mineral composition like Ft. Knox and main cities, but if they are like us who believe we are somehow outside of nature and unique, they probably make up a perfectly scientific explanation that excludes intelligent life before them.
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Re: Greenland ice sheet retreat
« Reply #26 on: December 24, 2016, 03:46:33 PM »
I am pretty sure that they will find evidence of the 450 or so nuclear power stations around the world.  I mean, the half life of plutonium is 250,000 years isn't it?


Most of those plants will be ground to dust by glaciation and then drained to the oceans once the glaciers melt. I imagine they would find places with unusual mineral composition like Ft. Knox and main cities, but if they are like us who believe we are somehow outside of nature and unique, they probably make up a perfectly scientific explanation that excludes intelligent life before them.


135k years might not be enough to get an ice age:
http://www.independent.co.uk/environment/climate-change/climate-change-co2-emissions-will-delay-next-ice-age-by-100000-years-a6810436.html

Most could still be under water rather than ground up by glaciation? but how much is washed out and spread by oceans and how much radioactive stuff still contained in underwater buildings or how much we would manage to remove before they do get submerged, I wouldn't like to guess. Plenty of concrete buried under sediment on ocean shelves and on land to find - the anthropocene has begun.

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Re: Greenland ice sheet retreat
« Reply #27 on: December 24, 2016, 04:44:30 PM »
I always wondered why we don't put or nuclear waste in subduction zones at the bottom of deep ocean trenches .. if I owned one I would certainly offer it as a disposal facility .
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Archimid

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Re: Greenland ice sheet retreat
« Reply #28 on: December 25, 2016, 03:16:54 AM »
135k years might not be enough to get an ice age


I don't know about that link. I think that CO2 decay is much faster than that.

This image makes sense to me, but I'm not sure if it has been debunked or not:

http://www.euanmearns.com/wp-content/uploads/2014/09/half_life1.png

I think the order of events will be rapid warming accompanied by rapid CO2 release, mostly from forests burning. Once the forests have burned and civilization is in ruins CO2 will stop climbing and in less than 10k years the world will be back to normal CO2 levels and well under way to the next glaciation.
I am an energy reservoir seemingly intent on lowering entropy for self preservation.

Tor Bejnar

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Re: Greenland ice sheet retreat
« Reply #29 on: December 25, 2016, 04:43:09 AM »
135k years might not be enough to get an ice age


I don't know about that link. I think that CO2 decay is much faster than that.

This image makes sense to me, but I'm not sure if it has been debunked or not:

http://www.euanmearns.com/wp-content/uploads/2014/09/half_life1.png

I think the order of events will be rapid warming accompanied by rapid CO2 release, mostly from forests burning. Once the forests have burned and civilization is in ruins CO2 will stop climbing and in less than 10k years the world will be back to normal CO2 levels and well under way to the next glaciation.


"...  The geological evidence from the 55 million year event and from earlier warming episodes suggests that such an addition is likely to raise average global temperatures by at least 5-6ºC,  and  possibly more, and that recovery of the Earth’s climate  in  the  absence  of any mitigation  measures  could  take  100,000  years  or more.   ..." from Climate change: evidence from the geological record - A statement from the Geological Society of London November 2010

We are at 1ºC increase now and have at least 1.5 'locked in'.  BAU will take us at least to 5, I suspect (and 100,000 years to recover by natural means).  The natural CO2 sequestering is slower at lower temperatures, so the last 50 ppm decrease takes much longer than the first 50 ppm reduction.
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Re: Greenland ice sheet retreat
« Reply #30 on: December 25, 2016, 02:19:39 PM »
Thanks Tor Bejnar, that's a great link.  I didn't know past sudden warming episodes had this thermal "inertia". Now I'm going to have to reevaluate my position. Some thoughts:

1. The warming episodes mentioned in the link happened in a much warmer world without ice on the poles.  I wonder what difference will Greenland and Antarctica ice have on the cooling. As I implied in my original post, probably volcanism and definitely a cooling effect from melt water while the ice lasts

2. I would like to know when these warmer episodes started in relation to Milankovitch cycles. Since the Holocene thermal maximum, Milankovitch cycles are in a downward cycle. If the prior warming events happened at Milankovitch low points that could explain the long recovery times. In our case, solar forcings will become negative for the next 100k years. Maybe that's enough to overwhelm CO2 forcing?

3. Looking at figure 2 on the following page : https://www.wunderground.com/climate/PETM.asp
  This time around is a very different event. The unatural warming rates might overwhelm the carbon cycle.


I admit tho, I'm pushing the argument to it's breaking point. Perhaps we do get a runaway CO2 effect which leads to runaway warming that lasts 100k years. Maybe it resets the planet to Cambrian like conditions.



I am an energy reservoir seemingly intent on lowering entropy for self preservation.

Neven

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Re: Greenland ice sheet retreat
« Reply #31 on: December 25, 2016, 10:22:10 PM »
Can we stay on-topic, please? There are different threads for almost every subject you can think of on this Forum.
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Re: Greenland ice sheet retreat
« Reply #32 on: December 26, 2016, 05:14:08 AM »
Can we stay on-topic, please? There are different threads for almost every subject you can think of on this Forum.

Thanks, Neven.

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Re: Greenland ice sheet retreat
« Reply #33 on: January 02, 2017, 08:05:52 PM »
Good recent summary here of the ice mass situation in Greenland: https://www.climate.gov/news-features/featured-images/greenland-ice-mass-loss-continued-2016

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Re: Greenland ice sheet retreat
« Reply #34 on: March 22, 2017, 01:13:06 PM »
So......here's what's "cooking"  ::) so far:

1)  Antarctic ice sheet set new record minimum....and is at seasonal record low now...

2)  Arctic ice sheet set record low maximum and is now at seasonal record low...

3)  OK Greenland....you're "up to bat."  What is Greenland going to do this year....???

We have a couple months until the "fun" (dark humor) even starts in Greenland.....but if Greenland has a bad year (high melt) that would certainly be a "hat trick" (for you hockey fans).

If the Beaufort clears out early again this year....which it certainly looks poised to do with the COMPLETE ABSENCE OF ICE OF ANY THICKNESS.....that warming water to the west of the Canadian Archipelago....even though it is NOT right next to Greenland.....will CERTAINLY impact Greenland indirectly by helping to melt the waters off the shores of the Greenland Archipelago which is next to northeastern Greenland.



 
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Re: Greenland ice sheet retreat
« Reply #35 on: March 22, 2017, 08:35:39 PM »
Re 1 and 2: technically not ice sheets.

Re 3: Greenland's ice mass hits a new low practically every year, as the link I posted in the previous comment indicates. How much the ice mass drops this year we have yet to find out, but yeah, I doubt this year will be an exception.

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Re: Greenland ice sheet retreat
« Reply #36 on: March 22, 2017, 09:10:34 PM »
Re 1 and 2: technically not ice sheets.

I wasn't actually talking about that aspect of it (the technical of whether they are or aren't ice sheets).  I was just pointing out that "EVENTS or "markers"" are now happening in BUNCHES.

1)  Arctic ice sheet minimum high
2)  Antarctic ice sheet minimum low

Those 2 have already happened at the same time (roughly speaking)....

If we add in another "high melt year" like Greenland had in 2012...........AND....if we have a fourth year in a row of record high temps in 2017....  The pounding of the drum of global warming is getting louder....





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Re: Greenland ice sheet retreat
« Reply #37 on: March 22, 2017, 10:29:07 PM »
Ice sheets are massive, land-based and are found in Greenland and Antarctica.
Not really sure what the sea ice cover is called, but "ice sheet" is the wrong term and detracts from what you're trying to say.
« Last Edit: March 22, 2017, 10:37:20 PM by oren »

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Re: Greenland ice sheet retreat
« Reply #38 on: March 23, 2017, 12:09:46 PM »
I guess: 
'Ice shelf', where the floating ice is an extension / extrusion of a glacier or grounded ice field,
and
'Ice pack' where the floating ice is not attached to land. 
??

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Re: Greenland ice sheet retreat
« Reply #39 on: March 23, 2017, 08:29:32 PM »
Canadian Ice Service, Ice Glossary:

Drift/pack ice 
Term used in a wide sense to include any area of ice, other than fast ice, no matter what form it takes or how it is disposed. When concentrations are high, i.e., 7/10 or more, the term pack ice is normally used. When concentrations are 6/10 or less the term drift ice is normally used.

Ice field
Area of floating ice, consisting of any size of floes and greater than 10 km across.


Lots more here:
https://www.ec.gc.ca/glaces-ice/default.asp?lang=En&n=501D72C1-1

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Re: Greenland ice sheet retreat
« Reply #40 on: March 23, 2017, 11:47:58 PM »
Jason Box and crew, readying their research season on the Greenland ice.

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Re: Greenland ice sheet retreat
« Reply #41 on: April 16, 2017, 02:38:16 PM »
A new study pinpoints the year ca 1997 as a tipping point for GICs mass balance.

..we identify 1997 (±5 years) as the year after which the GICs refreezing regime starts to decrease and diverges significantly from the GrIS refreezing regime (black point in Fig. 3c). This marked reduction in refreezing capacity is representative of a deteriorating firn layer, the porous, multiyear snow layer between surface fresh snow (∼350 kg m−3) and the underlying ice (∼900 kg m−3). Decades of increased melt have reduced pore space to such a degree that enhanced refreezing can no longer compensate for increased meltwater production. Because it would take decades to regrow a healthy firn layer, we interpret 1997 as a tipping point in the mass balance of Greenland’s GICs.


Covering a total area of ∼90,000 km2, Greenland’s peripheral glaciers and ice caps (GICs) represent ∼12% of the world’s glacierized area outside of the Antarctic and Greenland ice sheets1. Greenland’s GICs account for 14 to 20% of total current Greenland glacial mass loss2, although they only represent ∼5% of the area and ∼0.5% (∼39 mm SLE) of the volume of the Greenland ice sheet (GrIS). In a scenario of continued global warming, Greenland’s GICs may lose 19–28% (7.5–11 mm) of their volume by 2100 (ref. 3).




Here we use a novel, 1 km surface mass balance product, evaluated against in situ and remote sensing data, to identify 1997 (±5 years) as a tipping point for GICs mass balance. That year marks the onset of a rapid deterioration in the capacity of the GICs firn to refreeze meltwater. Consequently, GICs runoff increases 65% faster than meltwater production, tripling the post-1997 mass loss to 36±16 Gt−1, or ∼14% of the Greenland total. In sharp contrast, the extensive inland firn of the GrIS retains most of its refreezing capacity for now, buffering 22% of the increased meltwater production. This underlines the very different response of the GICs and GrIS to atmospheric warming. 


A tipping point in refreezing accelerates mass loss of Greenland’s glaciers and ice caps https://www.nature.com/articles/ncomms14730

Slice of Greenland ice melts into oblivion http://climatenewsnetwork.net/slice-greenland-ice-melts-oblivion/

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Re: Greenland ice sheet retreat
« Reply #42 on: July 17, 2017, 04:49:20 PM »
Here is more information on meltwater storage and mass balance calculations:

Cooper, M. G., Smith, L. C., Rennermalm, A. K., Miège, C., Pitcher, L. H., Ryan, J. C., Yang, K., and Cooley, S.: Near surface meltwater storage in low-density bare ice of the Greenland ice sheet ablation zone, The Cryosphere Discuss., https://doi.org/10.5194/tc-2017-107, in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2017-107/

Abstract. We document the density and hydrologic properties of bare, ablating ice in a mid-elevation (1215 m a.s.l.) supraglacial internally drained catchment near Kangerlussuaq, southwest Greenland. We find water saturated, low-density (474–725 kg m−3, μ = 688 kg m−3) ice to at least 1.1 m depth below the ice sheet surface. This near surface, low-density ice consists of alternating fractured porous ice and clear solid ice lenses, overlain by a thin (< 0.5 m), even lower density (326–555 kg m−3, μ = 455 kg m−3) unsaturated weathering crust. Ice-density data from 10 shallow (0.9–1.1 m) ice cores along an 800 m transect suggest an average 15–22 cm of liquid meltwater storage within this low-density ice. Water saturation of this ice is confirmed through measurable water levels (1–29 cm, μ = 10 cm) in 84 % of cryoconite holes and rapid infilling of 83 % of 1 m drilled holes sampled along the transect. Though preliminary, these findings are consistent with descriptions of shallow, depth-limited aquifers in weathering crusts of temperate and polythermal glaciers worldwide, and confirm the potential for substantial transient meltwater storage within porous low-density ice on the Greenland Ice Sheet ablation zone surface. A conservative estimate for the ~ 63 km2 catchment yields 0.010–0.014 km3 of liquid meltwater storage in near-surface, low-density ice. Further work is required to determine whether these findings are representative of broader areas of the Greenland Ice Sheet ablation zone, and to assess the implications for sub-seasonal surface mass balance calculations, surface lowering observations from airborne and satellite altimetry, and supraglacial runoff processes.
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