Greenland will be far greater contributor to sea rise than expected

May 18, 2014
Penny Ice Cap outlet glacier on Baffin Island, Nunavut, Canada. Penny Ice Cap was previously surveyed from the air by the Airborne Topographic Mapper and CReSIS radar instrument teams in 1995, 2000 and 2005. Credit: Michael Studinger/NASA

Greenland's icy reaches are far more vulnerable to warm ocean waters from climate change than had been thought, according to new research by UC Irvine and NASA glaciologists. The work, published today in Nature Geoscience, shows previously uncharted deep valleys stretching for dozens of miles under the Greenland Ice Sheet.

The bedrock canyons sit well below sea level, meaning that as subtropical Atlantic waters hit the fronts of hundreds of glaciers, those edges will erode much further than had been assumed and release far greater amounts of water.

Ice melt from the subcontinent has already accelerated as warmer marine currents have migrated north, but older models predicted that once higher ground was reached in a few years, the ocean-induced melting would halt. Greenland's frozen mass would stop shrinking, and its effect on higher sea waters would be curtailed.

"That turns out to be incorrect. The glaciers of Greenland are likely to retreat faster and farther inland than anticipated – and for much longer – according to this very different topography we've discovered beneath the ice," said lead author Mathieu Morlighem, a UCI associate project scientist. "This has major implications, because the glacier melt will contribute much more to rising seas around the globe."

To obtain the results, Morlighem developed a breakthrough method that for the first time offers a comprehensive view of Greenland's entire periphery. It's nearly impossible to accurately survey at ground level the subcontinent's rugged, rocky subsurface, which descends as much as 3 miles beneath the thick ice cap.

On April 8, 2011, IceBridge flew a mission to coastal areas in southwest Greenland. Mountains and an open-water fjord surround one of the mission's targets, a small ice cap called Sukkertoppen Isflade. Credit: Michael Studinger/NASA

Since the 1970s, limited ice thickness data has been collected via radar pinging of the boundary between the ice and the bedrock. Along the coastline, though, rough surface ice and pockets of water cluttered the radar sounding, so large swaths of the bed remained invisible.

Measurements of Greenland's topography have tripled since 2009, thanks to NASA Operation IceBridge flights. But Morlighem quickly realized that while that data provided a fuller picture than had the earlier radar readings, there were still major gaps between the flight lines.

To reveal the full subterranean landscape, he designed a novel "mass conservation algorithm" that combined the previous ice thickness measurements with information on the velocity and direction of its movement and estimates of snowfall and surface melt.

The difference was spectacular. What appeared to be shallow glaciers at the very edges of Greenland are actually long, deep fingers stretching more than 100 kilometers (almost 65 miles) inland.

"We anticipate that these results will have a profound and transforming impact on computer models of evolution in Greenland in a warming climate," the researchers conclude.

"Operation IceBridge vastly improved our knowledge of bed topography beneath the Greenland Ice Sheet," said co-author Eric Rignot of UC Irvine and NASA's Jet Propulsion Laboratory. "This new study takes a quantum leap at filling the remaining, critical data gaps on the map."

The team also reported stark new findings last week on accelerated glacial melt in West Antarctica. Together, the papers "suggest that the globe's sheets will contribute far more to rise than current projections show," Rignot said.

Explore further: NASA data shed new light on changing Greenland ice

More information: Paper: dx.doi.org/10.1038/ngeo2167

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User comments : 30

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verkle
1.4 / 5 (20) May 18, 2014
It is scientifically dangerous to take measurments taken mostly in the last 4 years and try to extrapolate to what is going to happen 100-200 years from now. Doing so just creates unnecessary hype.

howhot2
4.5 / 5 (17) May 18, 2014
It is NOT! It's not scientifically dangerous to take measurements from the last 4 years and extrapolate. And it doesn't do anything to hype. The only thing hyped is whatever crap is in you mind. 4 years of data collecting on Greenland can provide thousand of year of knowlege on the climate history that has taken place. It's an amazing lengthy record of temperatures, gasses, dust, volcanic activity that can be deduced from ICE CORE samples. Just think of all of that history that is melting.

What's a few hundred meters of sea level rise among frends?
DonGateley
1 / 5 (11) May 19, 2014
I do believe that the part that is below sea level will contribute a net negative to the sea level rise because its density is lower than the water that will replace it.
ormondotvos
4.6 / 5 (10) May 19, 2014
These skeptic comments are tickling my funny bone, seriously. Gateley cracks me up.
runrig
4.7 / 5 (14) May 19, 2014
I do believe that the part that is below sea level will contribute a net negative to the sea level rise because its density is lower than the water that will replace it.


No.
Floating ice has a neutral effect as it displaces it's mass equivalent of water - Archimedes principle.
Grounded glaciers will add water to the Ocean.
runrig
4.7 / 5 (13) May 19, 2014
These skeptic comments are tickling my funny bone, seriously. Gateley cracks me up.

Bless....
Don't mock the afflicted...
There are many on here.
alfie_null
4.5 / 5 (16) May 19, 2014
It is scientifically dangerous to take measurments taken mostly in the last 4 years and try to extrapolate to what is going to happen 100-200 years from now. Doing so just creates unnecessary hype.

Nothing in the article suggests extrapolating four years to anything. Or measuring change over four years, for that matter. Are you being disingenuous, or are you simply not smart enough to understand the article?

One aspect of science that seems to be a challenge for you is learning to accept knowledge that you don't like. Spreading FUD accomplishes nothing scientifically, and (as you should have learned) gets you resoundingly criticized.
Agomemnon
1.3 / 5 (15) May 19, 2014
Since there has been no warming for 17 years (and counting), what's the point of the concern?
EnricM
5 / 5 (8) May 19, 2014
It is scientifically dangerous to take measurments taken mostly in the last 4 years and try to extrapolate to what is going to happen 100-200 years from now. Doing so just creates unnecessary hype.



why?

Can you explain that?
Caliban
4.6 / 5 (11) May 19, 2014
Since there has been no warming for 17 years (and counting), what's the point of the concern?


From the article:

"Ice melt from the subcontinent has already accelerated as warmer marine currents have migrated north, but older models predicted that once higher ground was reached in a few years, the ocean-induced melting would halt. Greenland's frozen mass would stop shrinking, and its effect on higher sea waters would be curtailed.'' ""That turns out to be incorrect. The glaciers of Greenland are likely to retreat faster and farther inland than anticipated – and for much longer – according to this very different topography we've discovered beneath the ice,"

[...]
The difference was spectacular. What appeared to be shallow glaciers at the very edges of Greenland are actually long, deep fingers stretching more than 100 kilometers (almost 65 miles) inland.


Simple reading comprehension, menomenop.

Adult Learning classes might help.



Agomemnon
1.4 / 5 (11) May 19, 2014
@Caliban - great. More unscientific nonesense from the emperically illiterate.

So there has been no warming for 17 years (and counting) and we have glaciers (which have always moved) moving, growing retreating whatever.

So what is your plan for holding the earth's ice still?
none. ok. So now what? Call me names because I don't care about useless fear mongering?
great plan.
supamark23
4.7 / 5 (13) May 19, 2014
So there has been no warming for 17 years (and counting) and we have glaciers (which have always moved) moving, growing retreating whatever.


You're completely wrong, we've continued warming but the rate of atmospheric warming has slowed (while the oceans have not slowed their warming at all).
Caliban
4.6 / 5 (11) May 19, 2014
@Caliban - great. More unscientific nonesense from the emperically illiterate.

So there has been no warming for 17 years (and counting) and we have glaciers (which have always moved) moving, growing retreating whatever.

So what is your plan for holding the earth's ice still?
none. ok. So now what? Call me names because I don't care about useless fear mongering?
great plan.


No, menomenop, I ridicule you because you ignored the relevant facts, which were very clearly stated in the article itself.

Instead, you chose to raise a thouroughly debunked --as pointed out by supamark23-- yet irrelevant, argument in your comment.

Therefore, either you are trolling, or were experiencing a reading comprehension deficit.

So --which is it?
Agomemnon
1.4 / 5 (11) May 19, 2014
still waiting for the plan to hold earths glaciers still...
DonGateley
1 / 5 (5) May 19, 2014
As ice melts, the water it becomes has a smaller volume. If that ice is below sea level and there is a path to the sea won't water flow into it's space from the sea to fill the vacated volume? If that's wrong I'd appreciate some logic instead of moronic knee jerks from people who get their sad little egos filled by ridiculing.

Another way to show it is to anchor a block of ice below the surface in a container of water. The level of the water will lower as it melts. As ice slides off a land slope into water of course it will increase the water's level but the dynamic is reversed if it's below the water level to begin with.
thermodynamics
5 / 5 (9) May 19, 2014
DG said:
Another way to show it is to anchor a block of ice below the surface in a container of water. The level of the water will lower as it melts. As ice slides off a land slope into water of course it will increase the water's level but the dynamic is reversed if it's below the water level to begin with.


Yes, if that is the way it was, that would be correct. However, you are doing the wrong experiment. Take an ice cube from outside the container and drop it into the glass. The level of water in the container will go up no matter where you take the ice from outside the container. It can be above it or below it. The only way that your version will work is if the water from the ocean can flow into the volume that was taken up by the ice. An example would be death valley with an altitude 86 m below sea level. If a glacier were in there and had to flow up to get to the ocean (yes glaciers go up and down the terrain) unless the water flowed back in the ocean would rise.
thermodynamics
5 / 5 (9) May 19, 2014
Cont for DG: If the ice if floating in the water it is neutral. If the ice is not in the water (but on the land) it is always positive unless the ice is replaced by the ocean water it is flowing into. If ice is below the water, as in your example, it is a negative effect and the ocean level would go down. Please let me know where to look for the ice that is chained to the bottom of the ocean.
Caliban
5 / 5 (8) May 19, 2014
As ice melts, the water it becomes has a smaller volume. If that ice is below sea level and there is a path to the sea won't water flow into it's space from the sea to fill the vacated volume? If that's wrong I'd appreciate some logic instead of moronic knee jerks from people who get their sad little egos filled by ridiculing.

Another way to show it is to anchor a block of ice below the surface in a container of water. The level of the water will lower as it melts. {{{ As ice slides off a land slope into water of course it will increase the water's level}}} but the dynamic is reversed if it's below the water level to begin with.


There you are, DG --you've just answered your own question.

As these "channelled" Greenland glaciers are melted by seawater, the tributary glaciers and possibly interior ice that feed into them, as well as the .above sea level portion of the glacier become "unblocked" and essentially drain into the sea, thereby raising sea level.

DonGateley
3 / 5 (1) May 19, 2014
@DG:

"The only way..."

Thanks for a considered response. That is the scenario I imagined for which I proposed an analogy. If the Greenland situation is other than that could you explain what it actually is? How can ice below sea level that is not floating make other than a negative contribution to the rise of what water surrounds it when it melts?
Caliban
5 / 5 (7) May 19, 2014
....Another way to show it is to anchor a block of ice below the surface in a container of water. The level of the water will lower as it melts. {{{ As ice slides off a land slope into water of course it will increase the water's level}}} but the dynamic is reversed if it's below the water level to begin with.


There you are, DG --you've just answered your own question.

As these "channelled" Greenland glaciers are melted by seawater, the tributary glaciers and possibly interior ice that feed into them, as well as the .above sea level portion of the glacier become "unblocked" and essentially drain into the sea, thereby raising sea level.

Caliban
5 / 5 (4) May 19, 2014
Apologies for double posting, everyone.
runrig
5 / 5 (7) May 20, 2014
@DG:

"The only way..."

Thanks for a considered response. That is the scenario I imagined for which I proposed an analogy. If the Greenland situation is other than that could you explain what it actually is? How can ice below sea level that is not floating make other than a negative contribution to the rise of what water surrounds it when it melts?

DG
If (it's base) is below sea level then it is displacing water.
If it is freely floating then there will be a neutral effect as in Archimedes principle.
If it is grounded, it is not fully displacing its mass as water - then as it melts it will ADD to the ocean volume.
The point is that the Antarctic ice sheets are NOT fully displacing their mass of ocean.
It is just that they are restrained from sinking deeper because the sea-bed is in the way.
Whydening Gyre
5 / 5 (7) May 20, 2014
Just a point of definition - aren't glaciers defined by their position on land, not in the sea? Therefore, any glacial melt would CONTRIBUTE to sea rise, right?
However I do see Runrig's point about ice on the seabed. If more than a seventh (or was it an eighth?) of an ice mass is above the water line, it will also add to sea level.
Whydening Gyre
5 / 5 (3) May 20, 2014
Apologies for double posting, everyone.

Sometimes phys.org doesn't refresh after submitting a post. Just do a refresh after your 1st submission, if it doesn't.
Whydening Gyre
5 / 5 (3) May 20, 2014
Cont for DG: If the ice if floating in the water it is neutral. If the ice is not in the water (but on the land) it is always positive unless the ice is replaced by the ocean water it is flowing into. If ice is below the water, as in your example, it is a negative effect and the ocean level would go down. Please let me know where to look for the ice that is chained to the bottom of the ocean.

A possibility, Thermo. Isn't methane an ice on ocean floor (or just beneath)? Might not water ice be locked in with it?
thermodynamics
5 / 5 (8) May 20, 2014
Cont for DG: If the ice if floating in the water it is neutral. If the ice is not in the water (but on the land) it is always positive unless the ice is replaced by the ocean water it is flowing into. If ice is below the water, as in your example, it is a negative effect and the ocean level would go down. Please let me know where to look for the ice that is chained to the bottom of the ocean.

A possibility, Thermo. Isn't methane an ice on ocean floor (or just beneath)? Might not water ice be locked in with it?

That is right. The density of methane clatherate is about 0.9, however, it is not the ice you would find in a glacier. I do give you points for pulling that one out though.
animah
5 / 5 (2) May 20, 2014
Also worth noting: This would decrease ocean salinity at the top of the Atlantic thermohaline circuit.

Freshwater "floats" on salt water (it's less dense). If that were to weaken the oceanic conveyor belt that confers Western Europe its climate, it would experience a small ice age.

To whit: The middle of Spain is at the same latitude as New York...
aksdad
1 / 5 (6) May 21, 2014
We anticipate that these results will have a profound and transforming impact on computer models of ice sheet evolution in Greenland in a warming climate.

Perhaps, but until you can measure the impact in the real world, it's simply a guess. Computer models do not necessarily reflect what's actually going on.

So far it seems global sea level rise has remained remarkably constant over the last century or so despite alarm over the melting of Greenland and West Antarctica ice sheets.

Global sea level 1807-2001
http://www.climat...els.html

Global sea level from tide gauges
http://sealevel.colorado.edu/content/tide-gauge-sea-level" title="http://http://sealevel.colorado.edu/content/tide-gauge-sea-level" rel="nofollow" target="_blank">http://sealevel.c...ea-level

Global sea level from satellite telemetry, 1993-present
http://sealevel.colorado.edu/
Caliban
5 / 5 (7) May 22, 2014
We anticipate that these results will have a profound and transforming impact on computer models of ice sheet evolution in Greenland in a warming climate.

Perhaps, but until you can measure the impact in the real world, it's simply a guess. Computer models do not necessarily reflect what's actually going on.

So far it seems global sea level rise has remained remarkably constant over the last century or so despite alarm over the melting of Greenland and West Antarctica ice sheets.

Global sea level 1807-2001
http://www.climat...els.html


No, it hasn't, aks

Quite the opposite to your assertion, it has actually accelerated in the past 20 or so years over the rate from earlier in the 20th century.

This, I pointed out to you from the very same sources you cited in another thread, and just yesterday, in fact.

So now it can be unequivocally stated that you are promulgating a deliberate lie.

animah
5 / 5 (6) May 22, 2014
Also aks, the source you supplied, http://sealevel.colorado.edu/ clearly shows a linear sea level increase - in direct opposition with your opinion.

See in particular: the graph titled "2014_rel3: Global Mean Sea Level Time Series (seasonal signals removed)".