Arctic Sea Ice : Forum

Cryosphere => Greenland and Arctic Circle => Topic started by: werther on January 17, 2015, 12:43:06 AM

Title: Greenland ice sheet retreat
Post by: werther on January 17, 2015, 12:43:06 AM
(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FGISextentcomparison20092012small_zpsbab2ad6b.jpg&hash=8d01d6d7f717e2731d7d691329f9e31b)

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.

Title: Re: Greenland ice sheet retreat
Post by: werther on January 17, 2015, 01:11:42 AM
Illustrating the details 1.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FJokullhlaupdetailJuly2012_zps1ee6b5bf.jpg&hash=b85af19be56110f40d1d75db1caca38b)

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.
Title: Re: Greenland ice sheet retreat
Post by: Neven on January 17, 2015, 08:03:06 AM
Very nice, Werther. Impressive.
Title: Re: Greenland ice sheet retreat
Post by: werther on January 19, 2015, 10:22:57 PM
Detail 2: Southwest Greenland; the complicated glacier-cross near the Kangertittivatsiaq and Angmagssalik.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FGlaciercrossJuly2012_zps88e0ce12.jpg&hash=39c51fca5d64e86111dc1c2d4db7ec2f)

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.
Title: Re: Greenland ice sheet retreat
Post by: Espen 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
Title: Re: Greenland ice sheet retreat
Post by: werther on January 20, 2015, 10:16:50 AM
Detail 3: Helheim glacier, southwest Greenland

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FHelheimJuly2012_zps01e94f55.jpg&hash=ca0050d08621d4ef0dd474a821b883ac)

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.
Title: Re: Greenland ice sheet retreat
Post by: werther on January 21, 2015, 09:31:00 AM
Detail 4: A.P. Bernstoff Glacier, SW Greenland

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FAPBernstoffGlacierJuly2012_zps24870be0.jpg&hash=1bb3c989fa78659e8d3cd477fd373aed)

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.
Title: Re: Greenland ice sheet retreat
Post by: werther on January 21, 2015, 10:27:00 AM
Detail 5: East Qorqup Glacier, South Greenland
The region East of Narsarssuaq; Qooroq- and Tunulliarfik Fjords

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FEastQorqupJuly2012_zps81686760.jpg&hash=8b51fb538565fdf6c2af08f190e45ef2)[/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/ (https://glacierchange.wordpress.com/2014/12/14/east-qorqup-glacier-terminus-disintegration-greenland/)
Title: Re: Greenland ice sheet retreat
Post by: werther 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.

(https://forum.arctic-sea-ice.net/proxy.php?request=http%3A%2F%2Fi1036.photobucket.com%2Falbums%2Fa446%2Fhanver1%2FClimate%25202015%2FInngiaIsbraeJuly2012_zps735cd000.jpg&hash=093c46656a7f1324d5df19e925344dde)

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.
Title: Re: Greenland ice sheet retreat
Post by: Gray-Wolf 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 (https://www.sciencedaily.com/releases/2016/12/161207133453.htm)
Title: Re: Greenland ice sheet retreat
Post by: Pmt111500 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)

(http://www.nature.com/nature/journal/v540/n7632/full/nature20146.html#affil-auth (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)
Title: Re: Greenland ice sheet retreat
Post by: Adam Ash 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 (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.
Title: Re: Greenland ice sheet retreat
Post by: Archimid on December 13, 2016, 01:29:19 PM
Quote
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.
Title: Re: Greenland ice sheet retreat
Post by: Tigertown 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.
Title: Re: Greenland ice sheet retreat
Post by: Hefaistos 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/
Title: Re: Greenland ice sheet retreat
Post by: Tigertown 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.
Title: Re: Greenland ice sheet retreat
Post by: RoxTheGeologist 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.
Title: Re: Greenland ice sheet retreat
Post by: Tigertown 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.
Title: Re: Greenland ice sheet retreat
Post by: Archimid 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.
Title: Re: Greenland ice sheet retreat
Post by: RoxTheGeologist 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.

Title: Re: Greenland ice sheet retreat
Post by: TerryM 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
Title: Re: Greenland ice sheet retreat
Post by: Archimid 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.

Quote
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.

Quote
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 (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 (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.
Title: Re: Greenland ice sheet retreat
Post by: RoxTheGeologist 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.

Quote
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.

Quote
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 (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 (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.
Title: Re: Greenland ice sheet retreat
Post by: Stephen on December 24, 2016, 03:39:21 AM
Quote
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.
Title: Re: Greenland ice sheet retreat
Post by: Avalonian 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. 
Title: Re: Greenland ice sheet retreat
Post by: Archimid on December 24, 2016, 02:36:15 PM
Quote
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.
Title: Re: Greenland ice sheet retreat
Post by: crandles on December 24, 2016, 03:46:33 PM
Quote
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 (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.
Title: Re: Greenland ice sheet retreat
Post by: be cause 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 .
Title: Re: Greenland ice sheet retreat
Post by: Archimid on December 25, 2016, 03:16:54 AM
Quote
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 (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.
Title: Re: Greenland ice sheet retreat
Post by: Tor Bejnar on December 25, 2016, 04:43:09 AM
Quote
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 (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 (https://www.geolsoc.org.uk/~/media/shared/documents/policy/Climate%20Change%20Statement%20final%20%20%20new%20format.pdf?la=en) - 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.
Title: Re: Greenland ice sheet retreat
Post by: Archimid 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 (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.



Title: Re: Greenland ice sheet retreat
Post by: Neven 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.
Title: Re: Greenland ice sheet retreat
Post by: Shared Humanity 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.
Title: Re: Greenland ice sheet retreat
Post by: Paddy 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 (https://www.climate.gov/news-features/featured-images/greenland-ice-mass-loss-continued-2016)
Title: Re: Greenland ice sheet retreat
Post by: Buddy 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.



 
Title: Re: Greenland ice sheet retreat
Post by: Paddy 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.
Title: Re: Greenland ice sheet retreat
Post by: Buddy on March 22, 2017, 09:10:34 PM
Quote
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....





Title: Re: Greenland ice sheet retreat
Post by: oren 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.
Title: Re: Greenland ice sheet retreat
Post by: Adam Ash 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. 
??
Title: Re: Greenland ice sheet retreat
Post by: Cate 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 (https://www.ec.gc.ca/glaces-ice/default.asp?lang=En&n=501D72C1-1)
Title: Re: Greenland ice sheet retreat
Post by: Thomas Barlow on March 23, 2017, 11:47:58 PM
Jason Box and crew, readying their research season on the Greenland ice.
Title: Re: Greenland ice sheet retreat
Post by: prokaryotes on April 16, 2017, 02:38:16 PM
A new study pinpoints the year ca 1997 as a tipping point for GICs mass balance.

Quote
..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.

Quote
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).

(https://www.nature.com/article-assets/npg/ncomms/2017/170331/ncomms14730/images/w582/ncomms14730-f1.jpg)

Quote
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 (https://www.nature.com/articles/ncomms14730)

Slice of Greenland ice melts into oblivion http://climatenewsnetwork.net/slice-greenland-ice-melts-oblivion/ (http://climatenewsnetwork.net/slice-greenland-ice-melts-oblivion/)
Title: Re: Greenland ice sheet retreat
Post by: AbruptSLR 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, (https://doi.org/10.5194/tc-2017-107,) in review, 2017.

http://www.the-cryosphere-discuss.net/tc-2017-107/ (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.
Title: Re: Greenland ice sheet retreat
Post by: VeliAlbertKallio on August 02, 2017, 03:41:37 PM
I don't think GDF's lower limit is 4-degree ground inclination. The spatial spread of North Greenland Ice Sheet disallows an easy meltwater drainage from GrIS interior, a precondition for GDF disallowance for the rapid ice cap collapse (continued here from the discussion on "the 2017 Melt Season" thread: the impact of the pulverized sea ice on land ice melting in a long-term). Given conditions of Northern GrIS, GDF threshold is smaller than 3-4 degrees. I suggest reading:

Meyer, Robinson: "When Glaciers Transform Into Deadly 150-mph Avalanches - After happening only once in the 100-year record, catastrophic glacial collapse occurred twice in Tibet this summer", The Atlantic | Science, 18 October 2016. https://www.theatlantic.com/science/archive/2016/10/glaciers-can-collapse-in-seconds-not-years/504458/ (https://www.theatlantic.com/science/archive/2016/10/glaciers-can-collapse-in-seconds-not-years/504458/)

I would also suggest reading pp. 24-25 on rapid erosion forces on terminal state ice sheets here: https://www.academia.edu/33000316/MPs_to_review_UKs_role_in_Arctic_sustainability_-_24th_April_2017.docx (https://www.academia.edu/33000316/MPs_to_review_UKs_role_in_Arctic_sustainability_-_24th_April_2017.docx)  I will be updating the document regarding the spread of crevasse in North-West Greenland which appeared draining melt water along 80 km stretch 24/07/2016. Due to weak melt 2017 summer, this formation appears as dry depression with total length branching 250 km. (The finalized text is due by September/October 2017.)
Title: Re: Greenland ice sheet retreat
Post by: nukefix on August 02, 2017, 04:56:33 PM

As I commented elsewhere the slope of Greenland margin is small and not conducive to rapid runaway collapse than can happen on much steeper mountain glaciers.

ps. can you share the location of the NEGIS-crevasse you mention, it would be interesting to track it with Sentinel-1?
Title: Re: Greenland ice sheet retreat
Post by: VeliAlbertKallio on August 02, 2017, 11:07:14 PM
"As I commented elsewhere the slope of Greenland margin is small and not conducive to rapid runaway collapse than can happen on much steeper mountain glaciers. "
>
I offer GDF as a possible (probable) cause for Heindrich Ice Berg Calving (D-O) Events accompanied by other events such as: land-based GrIS hydrofracturing post-Arctic summer sea ice and in conjunction with the slip-slide effect (filling of subglacial dentures in bed rock by melt water) and rapid erosion effects, the rising heft of GrIS calving front gradually destabilising it to ever faster collapses, and the metamorphosis of cold and dry (hard) ice into warm and wet (honeycombed 'rotten' ice on the bottom third of the ice sheet [see page 19]).

"Can you share the location of the NEGIS-crevasse you mention, it would be interesting to track it with Sentinel-1?" The information below should offer the best chances to find it with Sentinel-1.

I re-enclose the rift image a year ago 24.07.2016. If you had read my paper with care, you should have seen this link to the original NASA image (ref: endnote No. 40).

My suggestion is that you open both links as separate tabs, you can then flip between the two:

https://worldview.earthdata.nasa.gov/?p=arctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2016-07-24&z=3&v=-462016.0215509016,-1726176.8272150634,-199872.02155090158,-1561056.8272150634

I also enclose it a year later as a link 23.07.2017 (for your comparison). You may see it also on 24.07.2017, but this shows only the NW section, whereas a day earlier you can notice the dry denture in ice extending and branching much further to the E-SE:

https://worldview.earthdata.nasa.gov/?p=arctic&l=VIIRS_SNPP_CorrectedReflectance_TrueColor(hidden),MODIS_Aqua_CorrectedReflectance_TrueColor(hidden),MODIS_Terra_CorrectedReflectance_TrueColor,Reference_Labels(hidden),Reference_Features(hidden),Coastlines&t=2017-07-23&z=3&v=-462016.0215509016,-1726176.8272150634,-199872.02155090158,-1561056.8272150634

Title: Re: Greenland ice sheet retreat
Post by: johnm33 on August 03, 2017, 11:08:45 AM
Nukefix
"As I commented elsewhere the slope of Greenland margin is small and not conducive to rapid runaway collapse than can happen on much steeper mountain glaciers."
from https://www.theatlantic.com/science/archive/2016/10/glaciers-can-collapse-in-seconds-not-years/504458/ (https://www.theatlantic.com/science/archive/2016/10/glaciers-can-collapse-in-seconds-not-years/504458/)
“You’re not talking about a glacier that fell off a mountain peak,” says Stephen Evans, a professor of geological engineering at the University of Waterloo. He studied the Kolka site in person soon after the event. “I walked up [the hillside] without breaking a sweat. Six degrees is almost flat for all intents and purposes.”
The EU got interested in the north face of mountains when they began to thaw. https://www.eea.europa.eu/data-and-maps/indicators/mountain-permafrost/mountain-permafrost-assessment-published-sep-2008 (https://www.eea.europa.eu/data-and-maps/indicators/mountain-permafrost/mountain-permafrost-assessment-published-sep-2008)
Title: Re: Greenland ice sheet retreat
Post by: nukefix on August 03, 2017, 11:48:01 AM
I re-enclose the rift image a year ago 24.07.2016. If you had read my paper with care, you should have seen this link to the original NASA image (ref: endnote No. 40).
I don't see a "rift", only some topography-related differences in brightness. They could be related to bedrock-topography but I don't see anything out of the ordinary. I'm also checking a stack of Sentinel-1 radar images via Google Earth Engine and everything looks fully normal.
Title: Re: Greenland ice sheet retreat
Post by: nukefix on August 03, 2017, 04:14:27 PM
Here's the mean backscatter of a large stack of Sentinel-1 HH SAR images taken this year. There's are several ice-streams in the picture but no rifts..
Title: Re: Greenland ice sheet retreat
Post by: VeliAlbertKallio on August 03, 2017, 05:27:31 PM
nukefix, Many thanks for your comment and for Sentinel check! I come to agree with you that topographic factor is here behind the water flow direction and edit my text accordingly.

When it comes to GDF, I maintain my concern that post Arctic summer sea ice, the summertime melting and rainfall becomes massive over North GrIS. I expect the heat waves and flash-floods  becoming a near continuous occurrence over the low-lying ice sheet in North Greenland within just a few summers of the opened Arctic Ocean.

I see this risk the same way as I see ice coming off car windscreen when it warms first, then soon after even the ice on my flat car bonnet detaches and comes out. Reduction of bind and the disappearing friction at the base of ice causes virtually flat-lying ice to fall off the bonnet. Whether you accept pushing my extrapolative analogy that far is a value judgement and I see the German decision to pull the plug from nuclear reactors on sea side better than British idea to build more.

In North GrIS it is the critical amount of water in ice that should cause a likewise ice detachment as meltwater takes too long to drain out especially as most of it is likely to become subglacial water deposits in North Greenland before it eventually makes its way out to the sea.

I see mountain GDFs as a symptomatic example of 'medium-scale' ice detachment events and I see this principle applicable also to the very largest scales - provided that there is enough surface melting and basal water accumulation involved. Growing hydrofracturing will be one of the key indicators before largest scale GDF is possible. There must be extensive meltwater pooling that drains water into moulins over very large areas (though not at all necessary that all ice base would need a water-layer).

johnm33, thanks also for your comment. The article: Gruber, S. and Haeberli, W., 2007. Permafrost in steep bedrock slopes and its temperature-related destabilization following climate change. Journal of Geophysical Research 112, p. F02S18, is particularly illuminating in the dangers of deep-penetrating melting of rocks (as seen this summer when a mountain collapsed into sea triggering a tsunami in Greenland killing 4 and injuring 10) and followed in this forum.

EU has done a foresighted job to foresee this risk as mountain rocks increasingly thaw.

I expect some of the ice sheet holding perimeter barriers in Greenland to collapse the same way: Frost creep has made ice to fill many crevasses in Greenland's bedrocks over the aeons which now begin to melt causing increasing collapses. Some of these events will be in very large scales like the event in Alaska, read the article cited in my paper on page 5, see ref: (endnote 13) gives the link to this: Summers, Chris : “Pilot discovers massive Alaska landslide that took huge chunk out of snow-capped mountain and unleashed millions of tons of rock into debris field stretching nearly SEVEN MILES”, The Daily Mail, 6 July 2016. http://www.dailymail.co.uk/news/article-3676603/Pilot-captures-incredible-photos-footage-massive-Alaska-landslide-took-huge-chunk-snow-capped-mountain-unleashed-millions-tons-rock-debris-field-stretching-nearly-SEVEN-MILES.html (http://www.dailymail.co.uk/news/article-3676603/Pilot-captures-incredible-photos-footage-massive-Alaska-landslide-took-huge-chunk-snow-capped-mountain-unleashed-millions-tons-rock-debris-field-stretching-nearly-SEVEN-MILES.html)

AMEG and John Nissen suggested me to add a potential shield area / continental slope margin failures in Greenland as one explanation for the Eemian tsunamis of Bahamas discussed by Hansen on page 6 and their re-emergence now. See refs. endnote 15 (summary article), endnote 16 (full paper):

Mooney, Chris (story) & Uhrmacher, Kevin (graphics): That's heavy - Climate-change warnings include rising seas and wild weather shifts. But giant flying boulders? The Washington Post, 28 November 2015. http://www.washingtonpost.com/sf/national/2015/11/28/oceans/?utm_term=.bc31ba561ec9 (http://www.washingtonpost.com/sf/national/2015/11/28/oceans/?utm_term=.bc31ba561ec9)

Hansen, J. et. al.: "Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2◦C global warming could be dangerous". Atmospheric Chemistry and Physics (Atmos. Chem. Phys.), 16, 3761–3812, 2016. doi:10.5194/acp-16-3761-2016
www.atmos-chem-phys.net/16/3761/2016/ (http://www.atmos-chem-phys.net/16/3761/2016/)  http://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.pdf (http://www.atmos-chem-phys.net/16/3761/2016/acp-16-3761-2016.pdf)


It obviously goes that our paper does not recommend sea side nuclear reactor construction. I am myself, however, a member of EFN (Environmentalists For Nuclear) and support them in principle when built in seismically stable areas, away from sea and riversides. The best option is the larger lakes where water table is near constant with no dangerous variations.

I believe the inconsisency German v. British/French is due to the latter possessing nuclear explosives (and that nuclear energy gives 'justification' for nuclear weapons). I would not oppose lakeside nuclear. Following closely election campaigning in Russia, Britain, US and France, I find it incomprehensible that the taxpayers in these countries truly wish to carbonize each others' taxpayers with nuclear weapons and would think it as a good way of spending their tax monies.

I re-enclose the rift image a year ago 24.07.2016. If you had read my paper with care, you should have seen this link to the original NASA image (ref: endnote No. 40).
I don't see a "rift", only some topography-related differences in brightness. They could be related to bedrock-topography but I don't see anything out of the ordinary. I'm also checking a stack of Sentinel-1 radar images via Google Earth Engine and everything looks fully normal.
Title: Re: Greenland ice sheet retreat
Post by: nukefix on August 04, 2017, 11:56:42 AM
Ice sheets that are grounded on an inward-sloping submarine bed are fundamentally unstable, for example WAIS. In Greenland this is not expected to happen as the topography of the bedrock is much more benign:

https://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf (https://www.the-cryosphere.net/7/499/2013/tc-7-499-2013.pdf)

Jakobshaven goes deep inland under present day sea level but it's narrow. Mean-image of S-1 over 2017 brings the movement out nicely..

ps. I'm not familiar with the acronym GDF?

Title: Re: Greenland ice sheet retreat
Post by: oren on August 04, 2017, 02:48:01 PM
ps. I'm not familiar with the acronym GDF?
I believe is means Glaciogenic Debris-Flow, but now sure how it's related to the discussion.
Title: Re: Greenland ice sheet retreat
Post by: gerontocrat on August 04, 2017, 03:25:13 PM
NASA GRACE analysis from 2002 shows almost linear Greenland Ice Sheet mass loss trend. When will AGW accelerate the loss ?
Title: Re: Greenland ice sheet retreat
Post by: nukefix on August 04, 2017, 03:46:16 PM
NASA GRACE analysis from 2002 shows almost linear Greenland Ice Sheet mass loss trend. When will AGW accelerate the loss ?
Arguably this already happened in the 1990's...but yes melting can potentially increase by a lot and we could have more summers with 2012-like extreme melt...
Title: Re: Greenland ice sheet retreat
Post by: Daniel B. on August 04, 2017, 04:35:20 PM
NASA GRACE analysis from 2002 shows almost linear Greenland Ice Sheet mass loss trend. When will AGW accelerate the loss ?

Certainly not this year.
Title: Re: Greenland ice sheet retreat
Post by: johnm33 on August 05, 2017, 12:23:36 PM
"When will AGW accelerate the loss ?"
When the meltwater of the interior gets access to the ocean?
Title: Re: Greenland ice sheet retreat
Post by: oren on August 05, 2017, 10:57:23 PM
"When will AGW accelerate the loss ?"
When the meltwater of the interior gets access to the ocean?
Indeed. Or when Zachariae Isstrom decides to let all hell break loose.
Title: Re: Greenland ice sheet retreat
Post by: johnm33 on August 06, 2017, 05:39:11 PM
It has to break out from the three rows of islands which are presently holding back it's melange and calving front, I begin to wonder if it'll have to wait to be weakened by ongoing melting to the north or south, although perhaps one almighty storm could clear it's path. That said it remains my favourite, there are so many ice streams falling into Jakobshavn that the fjord hardly ever clears, and Petermann tapers so much for so long, but maybe VAK is right.
Title: Re: Greenland ice sheet retreat
Post by: nukefix on August 07, 2017, 07:19:00 AM
"When will AGW accelerate the loss ?"
When the meltwater of the interior gets access to the ocean?
Indeed. Or when Zachariae Isstrom decides to let all hell break loose.
According to Bedmap2 there's only limited scope for retreat at NEGIS.
Title: Re: Greenland ice sheet retreat
Post by: AbruptSLR on May 14, 2018, 10:45:40 PM
It seems to me that the behavior of the NEGIS during the Holocene Optimum ~7.8 – 1.2 ka, provides a point of concern as to how much ice mass loss may occur for this key marine terminating ice stream in the coming decades:

Nicolaj K. Larsen et al. (14 May 2018), "Instability of the Northeast Greenland Ice Stream over the last 45,000 years", Nature Communications, Volume 9, Article number: 1872, doi:10.1038/s41467-018-04312-7

http://www.nature.com/articles/s41467-018-04312-7

Abstract: "The sensitivity of the Northeast Greenland Ice Stream (NEGIS) to prolonged warm periods is largely unknown and geological records documenting such long-term changes are needed to place current observations in perspective. Here we use cosmogenic surface exposure and radiocarbon ages to determine the magnitude of NEGIS margin fluctuations over the last 45 kyr (thousand years). We find that the NEGIS experienced slow early Holocene ice-margin retreat of 30–40 m a−1, likely as a result of the buttressing effect of sea-ice or shelf-ice. The NEGIS was ~20–70 km behind its present ice-extent ~41–26 ka and ~7.8–1.2 ka; both periods of high orbital precession index and/or summer temperatures within the projected warming for the end of this century. We show that the NEGIS was smaller than present for approximately half of the last ~45 kyr and is susceptible to subtle changes in climate, which has implications for future stability of this ice stream."
Title: Re: Greenland ice sheet retreat
Post by: vox_mundi on September 19, 2018, 01:25:18 AM
Study links natural climate oscillations in north Atlantic to Greenland ice sheet melt   (https://m.phys.org/news/2018-09-links-natural-climate-oscillations-north.html)

Quote
  Scientists have known for years that warming global climate is melting the Greenland Ice Sheet, the second largest ice sheet in the world. A new study from the Woods Hole Oceanographic Institution (WHOI), however, shows that the rate of melting might be temporarily increased or decreased by two existing climate patterns: the North Atlantic Oscillation (NAO), and the Atlantic Multidecadal Oscillation (AMO).

 Both patterns can have a major impact on regional climate. The NAO, which is measured as the atmospheric pressure difference between the Azores and Iceland, can affect the position and strength of the westerly storm track. The study found that when the NAO stays in its negative phase (meaning that air pressure is high over Greenland) it can trigger extreme ice melt in Greenland during the summer season. Likewise, the AMO, which alters sea surface temperatures in the North Atlantic, can cause major melting events when it is in its warm phase, raising the temperature of the region as a whole.

Depending on how the AMO and NAO interact, excess melting could happen two decades earlier than expected, or two decades later this century.

"We know the Greenland ice sheet is melting in part because of warming climate, but that's not a linear process," Ummenhofer said. "There are periods where it will accelerate, and periods where it won't."   
Title: Re: Greenland ice sheet retreat
Post by: vox_mundi on September 19, 2018, 10:36:38 PM
More evidence that Ice Caps like Greenland may exhibit fundamental instability once they pass a tipping point ...

Unprecedented Ice Loss In Russian Ice Cap
https://m.phys.org/news/2018-09-unprecedented-ice-loss-russian-cap.html

(https://3c1703fe8d.site.internapcdn.net/newman/csz/news/800/2018/20-unprecedente.jpg)

In the last few years, the Vavilov Ice Cap in the Russian High Arctic has dramatically accelerated, sliding as much as 82 feet a day in 2015, according to a new multi-national, multi-institute study led by CIRES Fellow Mike Willis, an assistant professor of Geology at CU Boulder. That dwarfs the ice's previous average speed of about 2 inches per day and has challenged scientists' assumptions about the stability of the cold ice caps dotting Earth's high latitudes.

... Researchers suspect the ice cap began to dramatically advance when the bottom of the ice cap became wetter and the front of the glacier advanced onto very slippery marine sediments.

By 2015, the sediments and rock at the bed beneath the ice had become so slippery that the material couldn't stop the ice from flowing. It took just two years for the ice cap base to reach that tipping point, transforming into a near frictionless zone, which is well-lubricated and highly mobile. The glacier continues to slide today at accelerated speeds of 5-10 meters per day.

The Vavilov Ice Cap thinned by a total of a few meters, advanced about 2 km, and lost about 1.2 km3 in total volume into the ocean in the 30 years before the speedup. In the one year between 2015 and 2016, the ice advanced about 4 kilometers and thinned by about 100 meters (~0.3 m per day). The ice cap lost about 4.5 km3 of ice, enough to cover Manhattan with about 250 feet of water, or the entire state of Washington with an inch. And it's unlikely the ice cap will ever be able to recover ice mass in today's warming climate, the paper states.
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Many scientists have assumed that polar ice caps that sit above sea level will only respond slowly to a warming climate—but the authors of this study urge that this assumption be questioned. The rapid collapse of the Vavilov Ice Cap has significant ramifications for glaciers in other polar regions, especially those fringing Antarctica and Greenland.   

Michael J. Willis et al, Massive destabilization of an Arctic ice cap (https://www.sciencedirect.com/science/article/pii/S0012821X18305156?via%3Dihub), Earth and Planetary Science Letters (2018)

Quote
Abstract:

  Ice caps that are mostly frozen at the bedrock-ice interface are thought to be stable and respond slowly to changes in climate. We use remote sensing to measure velocity and thickness changes that occur when the margin of the largely cold-based Vavilov Ice Cap in the Russian High Arctic advances over weak marine sediments. We show that cold-based to polythermal glacier systems with no previous history of surging may evolve with unexpected and unprecedented speed when their basal boundary conditions change, resulting in very large dynamic ice mass losses (an increase in annual mass loss by a factor of ∼100) over a few years. We question the future long-term stability of cold and polythermal polar ice caps, many of which terminate in marine waters as the climate becomes warmer and wetter in the polar regions.
Title: Re: Greenland ice sheet retreat
Post by: sidd on September 19, 2018, 10:41:28 PM
For those interested, I posted some quotes from the paper on the Vavilov icecap at

https://forum.arctic-sea-ice.net/index.php/topic,1350.msg173421.html#msg173421

in another thread.

sidd
Title: Re: Greenland ice sheet retreat
Post by: AbruptSLR on October 03, 2018, 11:49:52 PM
As continued global warming should increase the frequency with which atmospheric rivers reach Greenland, we may be in for some rude surprises in the coming decades (w.r.t. increasing rates of ice mass loss from the Greenland Ice Sheet):

William Neff (2018), "Atmospheric rivers melt Greenland", Nature Climate Change 8, 857-858, DOI: https://doi.org/10.1038/s41558-018-0297-4

http://www.nature.com/articles/s41558-018-0297-4

Abstract: "Recent years have seen increased melting of the Greenland Ice Sheet, contributing to accelerated rates of sea-level rise.  New research suggests that this melting due to an increased frequency of atmospheric rivers, narrow filaments of moist air moving polewards."
Title: Re: Greenland ice sheet retreat
Post by: sidd on October 04, 2018, 05:34:51 AM
Thanks for the Neff reference. Neff has been looking at the effect of atmospheric rivers on greenland forawhile, eg

doi: 10.1002/2014JD021470

which i believe i have discussed before.

The latest Neff article is a precis of the results of Mattingly et al. (Fettweis is an author)

doi:10.1029/2018JD028714

on the impact of atmospheric rivers on greenland ice over the period 1980-2016. The latter, among other things, use a self organizing map classifier to identify these phenomena. They find, unsurprisingly that the effect is spatially and seasonally diverse, but that surface mass balance is adversely affected.

"Furthermore, our investigation of the short- and long-term relationships between moisture transport events and modeled GrIS surface properties proves that this correspondence between the years of enhanced AR activity and anomalous GrIS mass loss is not a coincidence. Strong AR impacts cause increased melt in all areas of the GrIS and decreased SMB in the ablation zone during summer, and warm seasons with above-average GrIS melt extent are characterized by anomalously strong moisture transport by ARs over Greenland. ARs typically result in SMB gains in the GrIS ablation zone during nonsummer seasons and in the accumulation zone during all seasons. However, the intense summer SMB losses in the ablation zone during years of enhanced moisture transport outweigh the positive AR contributions to SMB in other regions and seasons. The scaling of melt versus snowfall in Figures 9 and 11 shows that the magnitude of mass loss from summer melt in the ablation zone has a much greater upper limit than mass gain from snowfall."

I attach figure 9.

sidd
Title: Re: Greenland ice sheet retreat
Post by: RoxTheGeologist on October 05, 2018, 05:47:58 PM

Less just hope that the large parts of the ice sheet doesn't get warm enough and well lubricated enough to collapse en-mass. The images of glaciers collapsing catastrophically in the Himalayas may set precedent for that to happen.

https://www.thethirdpole.net/en/2017/08/17/experts-explore-reasons-for-glacier-collapses-in-tibet/
Title: Re: Greenland ice sheet retreat
Post by: vox_mundi on June 19, 2019, 09:26:03 PM
New Research Shows an Iceless Greenland May Be In Our Future
https://phys.org/news/2019-06-iceless-greenland-future.html

https://youtu.be/LtpD-bAFQoc

Greenland's melting ice sheet could generate more sea level rise than previously thought if greenhouse gas emissions continue to increase and warm the atmosphere at their current rate, according to a new modeling study. The study, which used data from NASA's Operation IceBridge airborne campaign, was published in Science Advances today. In the next 200 years, the ice sheet model shows that melting at the present rate could contribute 19 to 63 inches to global sea level rise, said the team led by scientists at the Geophysical Institute at the University of Alaska Fairbanks. These numbers are at least 80 percent higher than previous estimates, which forecasted up to 35 inches of sea level rise from Greenland's ice.

The updated model more accurately represents the flow of outlet glaciers, the river-like bodies of ice that connect to the ocean. Outlet glaciers play a key role in how ice sheets melt, but previous models lacked the data to adequately represent their complex flow patterns. The study found that melting outlet glaciers could account for up to 40 percent of the ice mass lost from Greenland in the next 200 years.

... If greenhouse gas concentrations remain on the current path, the melting ice from Greenland alone could contribute as much as 24 feet to global sea level rise by the year 3000, which would put much of San Francisco, Los Angeles, New Orleans and other cities under water.

However, if greenhouse gas emissions are cut significantly, that picture changes. Instead, by 3000 Greenland may lose 8% to 25% of ice and contribute up to approximately 6.5 feet of sea level rise. Between 1991 and 2015, Greenland's ice sheet has added about 0.02 inches per year to sea level, but that could rapidly increase.

(https://advances.sciencemag.org/content/advances/5/6/eaav9396/F2.large.jpg)
Fig. 2 Observed 2008 state and simulations of the Greenland Ice Sheet at year 3000.
(A) Observed 2008 ice extent (53). (B to D) Likelihood (percentiles) of ice cover as percentage of the ensemble simulations with nonzero ice thickness. Likelihoods less than the 16th percentile are masked. (E) Multiyear composite of observed surface speeds (61). (F to H) Surface speeds from the control simulation. Basin names shown in (A) in clockwise order are southwest (SW), central-west (CW), northwest (NW), north (NO), northeast (NE), and southeast (SE). RCP 2.6 (B and F), RCP 4.5 (C and G), and RCP 8.5 (D and H). Topography in meters above sea level (m a.s.l.) [(A) to (H)].


(https://advances.sciencemag.org/content/advances/5/6/eaav9396/F3.large.jpg)
Fig. 3 Evolution of ice sheet area and mass balance components for the control simulation for each RCP scenario.
(A to C) Ice area evolution. (D to F) Partitioning of ice sheet wide mass balance rates into snow accumulation, runoff, and ice discharge into the ocean shown in Gt year−1 (D to F) and kg m−2 year−1 (left axis) and m year−1 ice equivalent (right axis) (G to I). We distinguish between runoff due to climate warming and runoff due to surface elevation lowering. (A) to (I) are plotted as 11-year running means.


Open Access: A. Aschwanden, et.al., Contribution of the Greenland Ice Sheet to sea level over the next millennium (https://advances.sciencemag.org/content/5/6/eaav9396)" Science Advances (2019)

Abstract:

The Greenland Ice Sheet holds 7.2 m of sea level equivalent and in recent decades, rising temperatures have led to accelerated mass loss. Current ice margin recession is led by the retreat of outlet glaciers, large rivers of ice ending in narrow fjords that drain the interior. We pair an outlet glacier–resolving ice sheet model with a comprehensive uncertainty quantification to estimate Greenland’s contribution to sea level over the next millennium. We find that Greenland could contribute 5 to 33 cm to sea level by 2100, with discharge from outlet glaciers contributing 8 to 45% of total mass loss. Our analysis shows that uncertainties in projecting mass loss are dominated by uncertainties in climate scenarios and surface processes, whereas uncertainties in calving and frontal melt play a minor role. We project that Greenland will very likely become ice free within a millennium without substantial reductions in greenhouse gas emissions.

(https://3c1703fe8d.site.internapcdn.net/newman/csz/news/800/2019/studypredict.gif)
Title: Re: Greenland ice sheet retreat
Post by: Killian on August 02, 2019, 05:50:31 AM
https://www.nationalgeographic.com/environment/2019/01/greeland-ice-melting-four-times-faster-than-thought-raising-sea-level/

The numbers from this National Geographic article, from January) are substantial for Greenland, unless I’m misunderstanding something. These doubling times are coming down to levels Hansen, et al. warned about some years ago; sub-10yr. That rate of melt is only going to accelerate. If this info is accurate and widespread, we’re looking at those dreaded 5-year doubling times, easily, it would seem.

My caveat is I suck at math. Anyone care to work out the the doubling times for the data in this article?

Context:
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All it takes to melt Greenland’s ice sheet is a surface temperature of 1 C and sunlight. “It used to be rare to get temperatures above 0 degrees on the ice sheet, but no longer,” Bevis said. And each degree above 1 C doubles the amount of ice melt….

However, there is a warming threshold that could be crossed in a few decades or less and, if exceeded long enough, the meltdown of Greenland would be irreversible, said Alley…

And it’s clear more of the overall ice loss is coming from the surface than marine terminating glaciers, Box said.

Measured Melt:
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Greenland… hit a tipping point around 2002-2003… By 2012 the annual ice loss was “unprecedented” at nearly four times the rate in 2003

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between 2002 and 2016, Greenland lost approximately 280 billion tons of ice per year.

How do those billions spread over those 13 years. It’s got to be a parabolic curve, yes? Well, more of a sawtooth rising, still. This is not happening monotonically or it wouldn’t have quadrupled in such a short time.

Not having the math skills to apply an equation to the info, I drew myself a simple parabolic curve (attached) with doubling, tripling and quadrupling on one axis and 2-year increments of time on the other, out to sixteen. I popped a generic parabolic curve into it and got 10 years for the first doubling and 6 for the second.

I’m very curious what the actual math is.

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It’s the same story for western North America’s glaciers—ice loss quadrupled since the early 2000s to 12.3 billion tons annually

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Alarmingly, the Antarctic is also undergoing an accelerated melt down, losing six times as much ice as it was four decades ago, a January 14 study reported. Its ice loss averaged 252 billion tons a year over the past decade.

https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2018GL080942
Title: Re: Greenland ice sheet retreat
Post by: oren on August 02, 2019, 09:22:36 AM
Ice loss accelerated until 2012 and then calmed down, relatively speaking, so the math isn't straightforward.
However, this year seems to be a near-repeat of 2012, so the curve should spike again.