NASA: Warm Ocean Currents Cause Majority of Ice Loss from Antarctica

Breaking news from NASA and the ICEsat team, that’s their headline, not mine.

This really makes all the hype over the now discredited Steig et al. paper, which attempted to establish an air temperature warming trend as one of the possible causes for “Antarctic melting”, only to have the Mannian PCA math they used shot down in flames for smearing data from the Antarctic Peninsula all over the continent, look even weaker.

Click for a larger image or visit the video animation page here

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

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

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

“We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt,” said the study’s lead author Hamish Pritchard of the British Antarctic Survey in Cambridge, United Kingdom. “The oceans can do all the work from below.”

To map the changing thickness of almost all the floating ice shelves around Antarctica, the team used a time series of 4.5 million surface height measurements taken by a laser instrument mounted on ICESat from October 2003 to October 2008. They measured how the ice shelf height changed over time and ran computer models to discard changes in ice thickness because of natural snow accumulation and compaction. The researchers also used a tide model that eliminated height changes caused by tides raising and lowering the ice shelves.

“This study demonstrates the power of space-based, laser altimetry for understanding Earth processes,” said Tom Wagner, cryosphere program scientist at NASA Headquarters in Washington.” Coupled with NASA’s portfolio of other ice sheet research using data from our GRACE mission, satellite radars and aircraft, we get a comprehensive view of ice sheet change that improves estimates of sea level rise.”

Previous studies used satellite radar data to measure the evolution of ice shelves and glaciers, but laser measurements are more precise in detecting changes in ice shelf thickness through time. This is especially true in coastal areas. Steeper slopes at the grounding line, where floating ice shelves connect with the landmass, cause problems for lower-resolution radar altimeters.

ICESat was the first satellite specifically designed to use laser altimetry to study the Earth’s polar regions. It operated from 2003 to 2009. Its successor, ICESat-2, is scheduled for launch in 2016.

“This study demonstrates the urgent need for ICESat-2 to get into space,” said Jay Zwally, ICESat project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “We have limited information on the changes in polar regions caused by climate change. Nothing can look at these changes like satellite measurements do.”

The new research also links the observed increase in melting that occurs on the underside of a glacier or ice shelf, called basal melt, and glacier acceleration with changes in wind patterns.

“Studies have shown Antarctic winds have changed because of changes in climate,” Pritchard said. “This has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica’s glaciers are responding rapidly to a changing climate.”

A different picture is seen on the Antarctic Peninsula, the long stretch of land pointing towards South America. The study found thinning of the largest ice shelf on the peninsula can be explained by warm summer winds directly melting the snow on the ice shelf surfaces. The patterns of widespread ocean-driven melting and summer melting on the Antarctic Peninsula can be attributed to changing wind patterns.

The study was carried out by an international team from the British Antarctic Survey, Utrecht University in Utrecht, Netherlands, the University of California in San Diego and the non-profit research institute Earth and Space Research in Corvallis, Ore.

For more information about ICESat and ICESat-2, visit:

http://icesat.gsfc.nasa.gov

==============================================================

I have the paper:

Antarctic ice-sheet loss driven by basal melting

of ice shelves

H. D. Pritchard, S. R. M. Ligtenberg, H. A. Fricker, D. G. Vaughan1, M. R. van den Broeke & L. Padman

doi:10.1038/nature10968

And I’ll be posting more on it later, for now, here is the summary:

To summarize, we find thinning attributed to ocean-driven basal melt on 20 of 54 ice shelves, with the most widespread and rapid losses (up to ~ 7m yr -1) on the coast of West Antarctica, where warm waters at depth have access to thick ice shelves via deep bathymetric troughs. There is evidence that changes in wind forcing explain both the

increased oceanic supply of warm water to thinning West Antarctic ice shelves, and the atmospheric warming on the Antarctic Peninsula that caused the loss of Larsen A and B and now dominates the thinning of Larsen C. That is to say, both processes are ultimately linked to the atmosphere. Both mechanisms imply that Antarctic ice shelves can respond rapidly to Southern Hemisphere wind patterns that vary on

timescales of years to decades.

We find that ocean-driven ice-shelf thinning is in all cases coupled with dynamic thinning of grounded tributary glaciers that together account for about 40% of Antarctic discharge and the majority of Antarctic ice-sheet mass loss2. In agreement with recent model predictions, we conclude that it is reduced buttressing from the thinning

ice shelves that is driving glacier acceleration and dynamic thinning.

This implies that the most profound contemporary changes to the ice sheets and their contribution to sea level rise can be attributed to ocean thermal forcing that is sustained over decades and may already have triggered a period of unstable glacier retreat.

And just in case people forget, the sea-ice trend in Antarctica is positive:

http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/seaice.anomaly.antarctic.png

Advertisements

  Subscribe  
newest oldest most voted
Notify of
Ian H

I have not read the paper. However it sounds like they measured – for the first time – the rate at which floating ice was melting from below. That sounds useful. We always knew ice melted from below but it is useful to quantify that.
However what puzzles me is how they can state that the rate of melting from below is accelerating since they have just got done with measuring it for the first time. The link to changing current patterns also seems a bit of a stretch. People have been looking at these currents for … how long? How can anyone realistically say they have changed?
It looks like a good bit of experimental measurement has been sexed up with a bunch of alarming and unjustified speculative statements to make it more appealing to a political rag like science.

nc

What sea level rise, and where is all that glacial ice coming from?

Mydogsgotnonose

Clearly no-one has done any engineering calculation of the enthalpies involved.
The real heating will be from reduction of cloud albedo due to phytoplankton blooms.

diogenes

just to say that, regardless of the scientifico/politico conclusions, that that is a beautiful picture of an unknown region of our planet.

edbarbar

I suppose what they are saying is the volume of ice is less, not the surface area of ice. What’s the purpose of showing the 2D surface area when the paper is discussing the 3D volume?

Well floating ice melts and contributes nothing to sea level rise. If what we are dealing with is a migrating glacier which is what they do, how does the ocean speed it up? The glaciers moving into the ocean cause sea level rise their melting just makes them less obvious.

Athelstan.

Gawd sakes, whatever next – Earth discovered to be in heliocentric orbit?

Bloke down the pub

The BBC tonight showed a programme of the Old Pulteney expedition to row to the magnetic pole as it was in 1996. Readers of this blog will know of this trip as it was followed on-line at the time. The thing that amused me was how they always seemed suprised when they came up against pack ice. Who would have thought it?

The Russians just bored thru 4,000 meters of ice into the fresh water Lake Vostok. This 14,000 sq km lake is the size of Lake Ontario, with an average surface temperature of -50F and 50 times the ambient dissolved Oxygen of typical fresh water lakes. Please, how did human Carbon Dioxide redirect OLR to keep this lake melted ? Maybe the HEAT, the fresh WATER and the free OXYGEN all come from BELOW !
See…. http://www.thelivingmoon.com/41pegasus/02files/Lake_Vostok02.html
….and then engage “brain”.

SirCharge

So sea ice cover measurably increased over the chosen time period but they used models to “prove” that the ice got thinner. Please explain how the warm currents managed to thin the ice without effecting it’s coverage.

Steve from Rockwood

From NASA and published in Nature. It’s got be right. Right? With that off my chest I’ll go read it anyway.

George E. Smith;

I have a simple experiment I would recommend to anyone who has doubts about how Antarctic ice sheets “melt”.
You need a stop watch, and a thermometer that includes zero deg C on its scale, and you need to find something like a mid west or similar cold lake that gets ice on it in winter. Night time is preferred to eliminate spurious “heat” sources like the sun.
So part one of the experiment requires waiting for a wind free night, with the air and water Temperature at the lake right at zero deg C, so there should be chunks of ice floating on the water.
You srtip down to your pre-natal suit, and start the stop watch as you stand alongside the lake shore.
Time how long it takes for you to freeze to death, or preferrably abandon this phase of the experiment, before that time.
Phase two of the experiment is identical to phase one, with one slight experimental difference in procedure.
Before you start the stop watch, as in phase one, go and jump in the lake.
Record the new time to expiration.
Then write a short essay, on the relative thermal conduction of air and water.
[Moderator’s Note: George, while there is a certain elegance to this experiment, don’t you think, maybe, you might have suggested that no one try this at home? -REP]

Philip Bradley

“We can lose an awful lot of ice to the sea without ever having summers warm enough to make the snow on top of the glaciers melt,” said the study’s lead author Hamish Pritchard of the British Antarctic Survey in Cambridge, United Kingdom. “The oceans can do all the work from below.”
I pointed out recently that the Antarctic Peninsula warming causing glacier/floating icesheet melt claim was fraudulent, because all the warming was at night, and night time temperatures hardly ever get above zero C.
The not warm enough to melt the snow on top claim, appears to derive from this point, but otherwise not based on any data.
Snow and ice can ‘melt’ from the top when temperatures are below zero, by sublimation, and increased solar insolation (from decreased clouds) will cause increased sublimation. Perhaps they have excluded this mechanism as the cause of icesheet melt, I can’t say from Anthony’s summary above.

What happened to the sticky Svensmark paper story….itv has dissapeared off WUWT current list???!!!

Paul Westhaver in a cranky mood

WASHINGTON — Warm ocean currents attacking the underside of ice shelves are the dominant cause of recent ice loss from Antarctica,
“ATTACKING” for gosh sakes!!!! attacking….
Who wrote this? What an A-hole.
Besides this ATTACK has been under way for 10,000 years….The BS never ends does it?

Big D in TX

Ah, now I understand! The missing heat was hiding under Antarctica, wringing its hands together and laughing to itself with all the devious intent of a silent film villain!
need I say /sarc?

bubbagyro

Ice floats. If it melts, total water level stays the same. If it doesn’t melt, water level stays the same. Middle school science. What a bunch of clowns to even go there.
Maybe I will pull the ice above the glass bar trick on them, and bet it doesn’t overflow!
“C’mon—Double or Nothing, professor!”
This is one of the useful properties of water that enables life on the planet.

That’s one for the history books surly? NASA in 2012 announces that they have discovered that Ice melts. (Yea of course, “and don’t call me surly”).
The usual culprits will have headlines like,
“ocean driving Antarctic ice loss”.
“Antarctic Ice Melting From Warm Water Below”.
“Warmer seas behind Antarctic ice shelf melt, study finds”
The spin on ice melting is very much on Que at the end of this this summer in the SH.
I wonder why? (hmm… scratches chin!)

Steve from Rockwood

I’m not sure how going from radar to laser helps you measure the removal of the underside of the ice.

Philip Bradley

And to pre-empt some of the icesheet -sea ice confusion. On the east side of the Antarctic Peninsula, where the Larsen icesheets are, you can see from the graphic below that sea ice extends far beyond the icesheets (300+ kms) even at this time year, the late Austral summer.
You can also see ice free areas along the coast, so warm ocean upwelling along the coast is certainly occuring. The question is whether it has increased.
http://nsidc.org/data/seaice_index/images/daily_images/S_bm_extent_hires.png

[Moderator’s Note: George, while there is a certain elegance to this experiment, don’t you think, maybe, you might have suggested that no one try this at home? -REP]
>>>>>>>
But he did. He said go to a lake. And to jump in it.

So… ocean currents have changed, bringing more warm water to the ice sheet, causing it to melt from below. Assuming that is correct:
1. Where did the warm water originate from?
2. What replaced the warm water? Presumably less warm water from somewhere else?
3. Since the warm water left where it was, and was replaced by other presumably colder water, did some area of earth experience cooling as a consequence?
4. If the volume of water melting from the ice sheet is in fact large enough to cause a measurable rise in sea level, then the obvious question is, where does that water go once it melts? Being at freezing point, it would be colder than any other water it flowed toward.
So, unless the study can show corresponding cooling to account for the change in warm water currents and the results of new cold water entering the ocean in vast quantities, all they’ve shown is…that something changed. Oh my. Like that’s never happened before.

Frank K.

But…but…the antarctic sea ice extent is above average right now
http://nsidc.org/data/seaice_index/images/daily_images/S_timeseries.png
and actually the arctic sea is pretty much at the historical average
http://nsidc.org/data/seaice_index/images/daily_images/S_timeseries.png
So…uh melting…ice free arctic…global warming…abnormal…catastrophic…I just don’t get it…

Frank K.

Whoops my second plot above one should be …
http://nsidc.org/data/seaice_index/images/daily_images/N_timeseries.png
Just “kissing” the historical average too. Go, baby ice, go!

Heystoopidone

Thanks Anthony, a most interesting read, in a world where 70% of the surface area is water, to be precise.
Antarctica, is a rather unique continent, with it’s very own current, which flows around the continent, unlike all other continents, as this diagram clearly shows :- http://en.wikipedia.org/wiki/File:Conveyor_belt.svg
So, by what mysterious mechanism are the oceans heating up again, since the initial around the world voyage of the oceanographic research vessel, the HMS Challenger, in 1873?

It’s Nature. I hate to ad hom, but in this case the stain on the rep is inky extreme. Lie to me a few hundred times, and I tend to lose confidence.
The floating ice is melting! It’s melting! Oh no!!!!!
Yeah, well, as the Award Winning Best Science Blogger points out: Antarctic ice mass in total is increasing. Good thing if some of the edge ice melts. There’s way too much ice in Antarctica anyway.
Ice is death. Nothing alive in frozen H2O, because Life requires liquid water. Anarctica is a Continent of Death. We pro-lifers (as opposed to pro-deathers) are not happy about that. What the Big World Gummit types ought to be doing is bombing the ice shelves and towing the bergs to places that could use it. Circulate and melt that dead ice. Do something useful with it.
WARMER IS BETTER. FIGHTTHE ICE.

Latitude

I don’t see a problem……Even where they were screaming “it’s breaking” is frozen over 10 times
http://nsidc.org/data/seaice_index/images/daily_images/S_bm_extent.png

Pamela Gray

So, the inference is that CO2 is now causing changes in winds. I am assuming less wind (exception would be Al Hansen). This is back to the old El Nino/CO2 connection that has already been shown to be FALSE.

Doug Proctor

A warmist talking point, clearly: oceans are warmer because of CO2 warming the air-water interface, causing the breakup of Antarctic ice shelves, which relieve the pressure on the inland glaciers, which then rush to the ocean and raise sea levels.

Philip Bradley

In the graphic above colour represents ice thickness, not as you might assume ocean temperature or ocean temp change.
Having read the NASA PR. There is no mention that they measured increased warm water upwelling.
The logic is icesheets are melting, warm water is upwelling, therefore upwelling warm water has caused the icesheet melt (in the sense of icesheet retreat).
Either the press release is badly written or the claim is junk.

David A. Evans

Athelstan. says:
April 25, 2012 at 3:57 pm

Gawd sakes, whatever next – Earth discovered to be in heliocentric orbit?

Seconded.
DaveE.

Latitude

ICESat was the first satellite specifically designed to use laser altimetry to study the Earth’s polar regions. It operated from 2003 to 2009.
=======
This is one of the biggest problems with any science that depends on nature cooperating….
They based everything on the info they have from 2003 – 2009….
….by the time they get their paper out there
it’s changed……
http://nsidc.org/data/seaice_index/images/daily_images/S_bm_extent.png

Pamela Gray

Predictions and WAGS about ice melt cause and effect are fraught with danger. For example, in March the powers that be said this about March’s Arctic ice extent:
“The ice that grew late this winter is quite thin, and will melt rapidly as the sun rises higher in the sky and the air and water get warmer.”
It does not appear to be melting rapidly yet. In fact, it seems to be hardly melting at all. It must really suck to say something in a published article, and to say it with such “we know about this stuff, you don’t” confidence, then have your boss tell you to quietly publish ANOTHER article about current conditions now, winking that you should never refer to how wrong you were last month.

kwinterkorn

I do not think the warm water is “attacking” the ice (warm water bad, ice good). I think the ice is sucking heat out of the warm water that innocently drifts by (ice bad, warm water good).
If these silly “scientists” can engage in asinine anthopomorphisms to suit their politics, so can I.

Anymoose

Did they really need a satellite and an army of PhD-candidates to figure this out? Some of these ice cakes have been watched for decades, with the expectation that they would eventually break away. The photographs show the whole story. Glacial ice pushed out far enough into the Antarctic Ocean until the stress on the land connection could no longer remain intact, and the ice cake broke away. Recon photos showed this gigantic ice cake was loose, and the warmists went into cardiac arrest over the whole situation.
The photos showed the surface of the ice cake was absolutely flat. That tells you that the top was not melting. The ocean water was slightly warmer than the ice. That is why it is water and not ice…….get it? It spent years melting off the underside of the ice cake until the lowering of the cake broke the land connection. And it does take a long time for water which may be only one degree warmer that the ice to remove the latent heat from the ice and turn some of the under surface into water.
If a 10th grade general science student could not figure this out he should be required to repeat the course.

Bill Illis

I don’t imagine that the same authors are responsible for this other paper published at the same time (well the names are exactly the same).
“Corrected ICESat altimetry data, surface mass balance, and firn elevation change on Antarctic ice shelves”
http://doi.pangaea.de/10.1594/PANGAEA.775982
Of course, the ICESat data needed to be corrected for … “We have modified the original ICESat data by applying an improved tide model (CATS2008a) as well as the recommended corrections for saturation and surface air pressure (the inverse barometer effect). … The original reported elevation relative to WGS84, as defined …. “

julie

“Studies have shown Antarctic winds have changed because of changes in climate,” Pritchard said. “This has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica’s glaciers are responding rapidly to a changing climate.”
I have no science qualifications at all but the above seems to say that climate change is driven by climate change.

Rushing – so have not had time to read all comments BUT…… could this melting ice have anything to do with all the undersea vents and volcano’s being discovered? Oceans warming….. from hot steam etc. Wondered also if these undersea activities which are spewing heat and chemicals into our ocean could be responsible for the die offs we are experiencing with dolphins etc…….

“Most of these are in West Antarctica, where inland glaciers flowing down to the coast and feeding into these thinning ice shelves have accelerated, draining more ice into the sea ”
Glaciers “flowing down” = growing glaciers
“draining more ice into the sea” = there is more sea ice, not less
“thinning ice shelves” … how can they be thinning if there is more ice?
Nature + NASA = Idiots

Willis Eschenbach

… ocean thermal forcing … may already have triggered a period of unstable glacier retreat

Man, I hate this kind of mush-mouthed, cowardly speculation that seems to be a climate scientists specialty …
w.

Roger

As I recall under the Antarctic peninsula (where all of Steig’s Heat was plastered over the whole of Antarctica comes from, there are quite powerful volcanic vents that spew out boiling water continuously (I haven’t got a clue how much this would heat up the water if at all)

Roger

looks like real-science.com is out of commission once again….
[Reply: Works for me. ~dbs, mod.]

Willis, could this be the beginning of a runaway …ocean thermal forcing.. effect? where the Ice acts as a blanket around the warm oceans reflecting back radiation? /jk

TomRude

“Studies have shown Antarctic winds have changed because of changes in climate,” Pritchard said. “This has affected the strength and direction of ocean currents. As a result warm water is funnelled beneath the floating ice. These studies and our new results suggest Antarctica’s glaciers are responding rapidly to a changing climate.”
A different picture is seen on the Antarctic Peninsula, the long stretch of land pointing towards South America. The study found thinning of the largest ice shelf on the peninsula can be explained by warm summer winds directly melting the snow on the ice shelf surfaces. The patterns of widespread ocean-driven melting and summer melting on the Antarctic Peninsula can be attributed to changing wind patterns.
=
In what is it different? It’s the winds and really too bad for warmists, from Antarctica the number of depressions below 980hPa coming out is increasing and the depressions are deeper -i.e. associated anticyclones are more powerful-… Leroux, Dynamic Analysis of Weather and Climate, Springer 2010 figures 14.10 and 14.11 and page 350 the conclusion is “the warming of the Antarctica peninsula is of dynamical origin”. Intensification of meridional exchanges causing transfer of additional warm, moist air to the Pole as a result of reinforced MPHs. This dynamic is precisely the opposite of what a global warming world should create. What the satellite offers is a confirmation and a precision on the various processes at work, not at all any confirmation of CO2 induced warming… quite the opposite!

Geoff Sherrington

Re Lake Vostok being liquid, can I ask again please, why are deep ocean waters so close to freezing point? The have a source of heat below (geothermal) and a source of heat above (the Sun). Until someone can explain why the ocean deeps are not as warm as the surface, I shall regard any global hypothesis about temperature, water and ice with great suspicion. When was the whole Ocean mass so cold before (if it was) and what caused the cooling?

George E. Smith

“”””” Geoff Sherrington says:
April 25, 2012 at 10:04 pm
Re Lake Vostok being liquid, can I ask again please, why are deep ocean waters so close to freezing point. “””””
What is the big mystery ? sea water of greater than about 2.47% salinity, increasess in density right down to its freezing point , and since it is denser when colder it sinks below warmer waters, so the deeper waters tend to be colder, until you get down to where the internal heating from the mantle, takes over and the cooling stops.
No mystery at all.

Willis Eschenbach

Geoff Sherrington says:
April 25, 2012 at 10:04 pm

Re Lake Vostok being liquid, can I ask again please, why are deep ocean waters so close to freezing point? The have a source of heat below (geothermal) and a source of heat above (the Sun). Until someone can explain why the ocean deeps are not as warm as the surface, I shall regard any global hypothesis about temperature, water and ice with great suspicion. When was the whole Ocean mass so cold before (if it was) and what caused the cooling?

First, the geothermal heat is generally small, on the order of a few hundredths of a watt per square metre. Yes, there’s more at the suboceanic vents that make such great TV … but in the immensity of the ocean floor those are few and far between.
Second, the oceans are constantly being fed very, very cold water from the poles. The water there is cooled. When it is cooled it sinks, and over time spreads across the bottom of the ocean. Here’s a cross-section:

“NADW” is North Atlantic Deep Water. “AABW” is Antarctic Bottom Water. Both sink because they are cold, with the AABW being the colder of the two. As a result, it ends up below the NADW.
And because the oceans are thermally stratified, warmest at the top and coldest at the bottom, the sun never gets to warm the bottom waters …
w.

wikeroy

“Studies have shown Antarctic winds have changed because of changes in climate,”
Or;
“Studies have shown Antarctic winds have changed the local climate,”

Keith Minto

What is surprising to me is the amount of bedrock below sea level in Antarctica, seen here. Compare this image with the header image and the idea of a solid, roughly round, Antarctica disappears. There are plenty of basins that would provide relief from ‘warmer’ currents.
The WA area was mentioned as having

…..warm waters at depth have(ing) access to thick ice shelves via deep bathymetric troughs.

OK, what temperatures are we talking about here, and what flow rates, for how long?
The impressive 80mb video seemed to show an irregular wind driven pattern of surface water movement that may not indicate subsurface direction, certainly does not look like the circumpolar current, and, if Tom Rude is correct,(above) warm moist Peninsular air will deposit as snow on this area, adding to the glacial flow.
What is it with Antarctica ?, do they think that this ‘unknown’ continent brimming over with scientists is their domain only and we will accept anything they say because of its remoteness?

Bill Tuttle

Steve from Rockwood says:
April 25, 2012 at 4:20 pm
I’m not sure how going from radar to laser helps you measure the removal of the underside of the ice.

You use a blue-green laser.
It’s amazingly accurate — if you sit on the bottom of the ocean and aim upwards…