Embracing data ‘noise’ brings Greenland’s complex ice melt into focus
by Morgan Kelly, Office of Communications, Princeton Universtity
An enhanced approach to capturing changes on the Earth’s surface via satellite could provide a more accurate account of how ice sheets, river basins and other geographic areas are changing as a result of natural and human factors. In a first application, the technique revealed sharper-than-ever details about Greenland’s massive ice sheet, including that the rate at which it is melting might be accelerating more slowly than predicted.
Princeton University researchers developed a mathematical framework and a computer code to accurately capture ground-level conditions collected on particular geographic regions by the GRACE satellites (Gravity Recovery And Climate Experiment), according to a report in the Proceedings of the National Academy of Sciences. A joint project of NASA and the German Aerospace Center, GRACE measures gravity to depict how mass such as ice or water is distributed over the Earth’s surface. A change in GRACE data can signify a change in mass, such as a receding glacier.
Typically, GRACE data are recorded for the whole globe and processed to remove large regional differences, said lead author Christopher Harig, a postdoctoral research associate in Princeton’s Department of Geosciences. The result is a coarse image that can provide a general sense of mass change, but not details such as various mass fluctuations within an area. Watch the video:
Princeton University researchers developed an enhanced approach to capturing changes on the Earth’s surface via satellite that could provide a more accurate account of how geographic areas change as a result of natural and human factors. In a first application, the technique brought the complexities of Greenland’s massive ice sheet into clearer focus. From 2003 to 2012, the ice sheet experienced patchy fluctuations in ice loss and gain, while the areas of greatest melt gradually migrated from the southeast to the northwest coast. (Video by Christopher Harig)
With their method, Harig and co-author Frederik Simons, an assistant professor of geosciences, can clean up data “noise” — the signal variations and distortions that can obscure satellite readings — and then recover the finer surface details hidden within. From this, they can configure regional information into a high-resolution map that depicts the specific areas where mass change is happening and to what degree.
“We try to do very little processing to the data and stay closer to the real signal,” Simons said. “GRACE data contain a lot of signals and a lot of noise. Our technique learns enough about the noise to effectively recover the signal, and at much finer spatial scales than was possible before. We can ‘see through’ the noise and recover the ‘true’ geophysical information contained in these data. We can now revisit GRACE data related to areas such as river basins and irrigation and soil moisture, not just ice sheets.”
From 2003 to 2010, Greenland overall lost roughly 200 billion tons of ice each year, but glacier activity was regionally inconsistent. Ice loss was concentrated on the southeast and northwest coasts for most of the period, but the area of greatest melt activity began to migrate from the southeast to the northwest coast around 2008. By 2010, the southeast coast displayed only minor ice loss. Meanwhile, the higher and colder interior gained ice mass, as did the southwest coast, slightly, from 2003 to 2006. (Image by Christopher Harig)
The researchers tested their method on GRACE data for Greenland recorded from 2003 to 2010 and brought the complexities of the island’s glaciers into clearer focus. While overall ice loss on Greenland consistently increased between 2003 and 2010, Harig and Simons found that it was in fact very patchy from region to region.
In addition, the enhanced detail of where and how much ice melted allowed the researchers to estimate that the annual acceleration in ice loss is much lower than previous research has suggested, roughly increasing by 8 billion tons every year. Previous estimates were as high as 30 billion tons more per year.
Douglas MacAyeal, a geophysical sciences professor at the University of Chicago, said that the research provides a standardized and accurate method for translating GRACE data, particularly for ice sheets. The sprawling, incomplete nature of the satellite’s information has spawned a myriad of approaches to interpreting it, some unique to specific scientists, he said.
“GRACE data is notoriously noisy and spatially spread out, and this has resulted in ‘ad hoc’ methods for processing mass changes of Earth’s ice sheets that have wildly different values,” said MacAyeal, who is familiar with the Princeton work but had no role in it.
“In other words, each particular investigator ends up getting a different individual number for the net change in mass,” he said. “What this research does is figure out a way to be more thoughtful and purposeful about exactly how to deal with GRACE’s notorieties. This method would allow researchers to standardize a bit more and also to understand more precisely where they are, and where they are not, able to resolve ice changes.”
Despite variations in glacier activity, Greenland experienced a steady ice loss of 200 billion tons annually, which could stack up on all of Manhattan to nearly 12,000 feet, or more than eight times taller than the Empire State Building. Nonetheless, the researchers estimated that the annual acceleration in ice loss is much lower than previous research has suggested, roughly increasing by 8 billion tons every year. Previous estimates were as high as 30 billion tons more per year. (Image by Christopher Harig)
Simons compared the noise that previously obscured a precise view of Greenland’s glaciers to fog on a window. For a small area such as Greenland, the GRACE signal can be easily overwhelmed by noise, which has numerous causes such as the satellite’s orbital position or even the type of mathematics researchers use to interpret data, Simons said.
“Other researchers used less than perfect tools to wipe off the window more or less indiscriminately and quite literally left streaks on the data. They were thus less able to put the continent into the proper focus,” he said.
“We effectively modeled then removed noise to get the ice-loss signal out of the data,” Simons said. “We then recovered relatively tiny variations in ice mass that to others might have looked like noise, but that to us were shown to be signal.”
The Princeton researchers found that Greenland lost roughly 200 billion tons of ice each year during the seven-year period studied, which falls within the range reported by other studies. The amount of ice lost annually could stack up on all of Manhattan to nearly 12,000 feet, or more than eight times taller than the Empire State Building, Harig said.
As expected, ice loss occurred in the lower, warmer coastal areas — as opposed to the higher and colder interior, which gained ice mass — but the melt was concentrated on the southeast and northwest coasts for most of the period studied. Indeed, many coastal areas showed no ice-mass loss, while the ice sheet on the southwest coast actually thickened slightly from 2003 to 2006.
But these trends were more complex when Harig and Simons got into the details. Surprisingly, the location of the greatest melt activity migrated around the island, shifting from the southeast to the northwest coast in just a few years. Ice loss on the southeast coast built up starting in 2003 and hit a highpoint in 2007. In 2008, loss on this coast began to recede and shift toward the northwest coast; by 2010, the southeast coast displayed only minor ice loss, while nearly the entire western coast exhibited the most severe melt. During this transition, melt also receded then picked up again on the northeastern coast with seemingly little overlap with activity elsewhere.
Details such as these can help scientists better understand the interplay between Greenland’s glaciers and factors that influence melt such as ocean temperature, daily sunshine and cloud coverage, Harig said. That understanding can in turn help researchers determine how the Greenland ice sheet responds to climate change — and how much more ice loss to expect. At current melt rates, the Greenland ice sheet would take about 13,000 years to melt completely, which would result in a global sea-level rise of more than 21 feet (6.5 meters), Harig said.
“Scientists are not totally sure what the driving force of the melt on Greenland is on short, yearly timescales,” Harig said. “There is no certainty about which outside factor is the most important or if all of them contribute. Being able to compare what is happening regionally to field observations from other researchers of what a glacier is doing helps us figure out what is causing all this melt.”
Michael Oppenheimer, Princeton’s Albert G. Milbank Professor of Geosciences and International Affairs, said that the new level of detail Harig and Simons provide on Greenland’s glaciers not only gives insight into what is causing the glaciers to melt, but what could possibly happen if they do.
Unlike water in a bathtub, sea-level rise is not uniform, said Oppenheimer, who is familiar with the research but had no role in it. Higher waters in certain locations may depend on which part of an ice sheet melts, he said. And determining which part of an ice sheet is melting the most requires precise details of ice loss and gain for specific glaciers — details that have largely been unavailable, Oppenheimer said.
“Nobody has really been able to take a look at an individual ice sheet and determine the influence that ice loss from different parts of that ice sheet could have on sea levels,” Oppenheimer said.
“The details matter. Being able to pinpoint where and how much ice gain and loss there is tells you something about the driving forces behind it, and therefore how much we can expect in the future,” he said. “A synoptic view at a high resolution is what GRACE always promised, and now this research has helped realize that potential. It’s time to finally milk the data for as much detail as possible.”
Harig is adapting the computer code — which is available online — to study GRACE data on ice loss in Antarctica and water accumulation in the Amazon River basin.
The paper, “Mapping Greenland’s mass loss in space and time,” was published online Nov. 19 in the Proceedings of the National Academy of Sciences. It was supported by a grant from the National Science Foundation.
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Here is some of Natalya Gomez’s fascinating modeling work as discussed above – in fact already published:
http://www.people.fas.harvard.edu/~phuybers/Doc/evolution_ice_sealevel.pdf
Evolution of a coupled marine ice sheet–sea level model
Natalya Gomez,1 David Pollard,2 Jerry X. Mitrovica,1 Peter Huybers,1 and Peter U. Clark3
Received 16 June 2011; revised 18 November 2011; accepted 6 December 2011; published 14 February 2012.
JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 117, F01013, doi:10.1029/2011JF002128, 2012
More Gomez etal 2012 … from the abstract:
http://www.people.fas.harvard.edu/~phuybers/Doc/evolution_ice_sealevel.pdf
Thanks Costco, that starts to answer my comment above.
Greenland mass balance down to -142 GT/year, Antarctic down to -60 GT/year. Contribution to sea level rise only +0.56 mms/year.
https://www.sciencemag.org/content/338/6111/1183
Looking at the graph of Greenland ice mass, I can’t figure out if the loss is a problem of losing ice faster or of not replacing the lost ice.
This is not a trivial situation to resolve. Greenland is a continental-style glacial mass that by material physics has to flow from the center thickness to the edges, where it both melts and calves into the sea. That is what glaciers do (which is why most of the alpine “glaciers” are not glaciers but stagnant ice masses, but tell that to an eco-green.) Unless there is continuous replacement in its heart, all glaciers will flow away until they are too thin to do so any more.
That being explained, any changes in Greenland have to deal with the two means of losing glacial mass. As we learned from the foolishness of the Kilamanjaro “glacier” stories of its extinction, non-replacement can be the reason all by itself (the loss of forest cover at the mountain’s base reduced the humidity and hence precipitation on the top of the mountain). Before we shriek about the Greenland loss to global warming, we need to address the replacement issue.
I believe, though could be again wrong, that there has been more sunshine since the mid-60s, and a lower humidity over Greenland. Both cause sublimation losses to be higher than before during the summer, regardless of temperature changes. If the winter snowfalls are also less than before, following on with the loss of general humidity, then much of the measured current loss could be accounted for by non-warming climatic changes and an associated non-replacement of surface loss. None of this is an aspect of temperature warming, by or not by CO2, but a drier, sunnier local climate.
Dunno. Just looking and thinking.
Bill Illis says: November 29, 2012 at 5:06 pm
“…Greenland mass balance down to -142 GT/year, Antarctic down to -60 GT/year. Contribution to sea level rise only +0.56 mms/year. …”
Or even less – see below. Gives rise to the question: Is Antarctica really melting?
Zwally etal 2011 would indicate no… well, only perhaps a contribution of 0.1 mm/year to SLR.
Two ERS-based estimates, the modified IOM, and a GRACE-based estimate for observations within 1992-2005 lie in a narrowed range of +27 to -40 Gt/year, which is about 3% of the annual mass input and only 0.2 mm/year SLE. Our preferred estimate for 1992-2001 is -47 Gt/year for West Antarctica, +16 Gt/year for East Antarctica, and -31 Gt/year overall (+0.1 mm/year SLE)…
http://icesat4.gsfc.nasa.gov/cryo_data/publications/Zwally-Giovinetto_SurveysInGeophysics_2011-1.pdf
So where does the current SLR come from? Maybe the groundwater guys are correct:
“…. have found, groundwater depletion is adding about 0.6 millimeters per year …. to the Earth’s sea level….” a team of Dutch scientists led by hydrologist Yoshihide Wada, Utrecht University. http://news.nationalgeographic.com/news/2012/05/120531-groundwater-depletion-may-accelerate-sea-level-rise/
Pokhrel estimates a 0.77 mm/year groundwater depletion contribution to SLR
… source: http://www.nature.com/ngeo/journal/v5/n6/full/ngeo1476.html
Has anyone figured out how much heat energy was required to melt that much ice? I wonder what the earh’s temperature would have been if the energy hadn’t been ‘used’ to melt the ice? Are we talking about a serious amount of heat energy or not? It would also give us an idea of what will happen to the earth’s temperature when all the ice is melted.
LetsBeReasonable says: November 29, 2012 at 5:56 pm
“…Has anyone figured out how much heat energy was required to melt that much ice?…”
Perhaps some clues from a publication on the last interglacial – The Eemian.
According to researchers it took temperatures equivalent to future IPCC ‘no action’ 2100 projections PLUS a massive increase in isolation: 60 Wm−2 compared to the 0.85 Wm−2 loading estimated to now occur from CO2 increases.
Significant contribution of insolation to Eemian melting of the Greenland ice sheet (2011) van de Berg etal http://www.staff.science.uu.nl/~broek112/home_files/MB_pubs_pdf/2011_vdBerg_NatGeo.pdf
CostCo
If there is substance to the the Princeton study that is the subject of this post, then your referred study has used obsolete processing of the satellite data, and therefore is unreliable. Poor scientists- all of that work for nought. Note their claim (at BBC) that their work settles the issue definitively.
Markx, it didn’t answer my question, I want to know how much heat energy has been used to melt the ice that has already melted. Then my next question is what would the Earth’s the temperature be if the ice hadn’t been melted and the heat retained in the atmosphere.
Roger Knights says: “GRACE’s Antarctic data is similarly analyzed. Those two findings, in combination with the recent debunking of recent Himalayan glacial loss, would throw a good deal of cold water on the warmists.”
Roger Knights says:”The “recent” I used referred to the last ten years, not the last 30 years.”
and refs Bradley: “ Did you know the Himalayas and nearby peaks have lost no ice in past 10 years?”
(missing lots, read the original posts if you are interested.)
Hmm. The Yao Nature paper is more recent than Bradley’s March ref. But that doesnt matter, you were arguing that the “warmists” had a problem with data, and Yao’s data is pretty extensive. (BTW, their supplementary data was outside the firewall for me, and they have great glacier pictures and maps in there, its worth the trip. Surprising Nature let them get away with it).
Anyway
actually the data is complicated, but the general idea is that glaciers a low elevations are melting, even in the last decade, and glaciers at high elevations (were it is always cold, even today) are growing. I’ll let you try to figure out why, but one hint (spoiler!) is that it is consistent with GW.
So, no, the warmists are always happy these days!
Doug Proctor says: “Greenland is a continental-style glacial mass that by material physics has to flow from the center thickness to the edges, where it both melts and calves into the sea. That is what glaciers do (which is why most of the alpine “glaciers” are not glaciers but stagnant ice masses, but tell that to an eco-green.) Unless there is continuous replacement in its heart, all glaciers will flow away until they are too thin to do so any more.”
Just how does a glacier know if it terminates in the sea or not? The only difference between a alpine glacier and a continental glacier is elevation and, in the case of Greenland and Antarctica, scale.
That said, quite a few glaciers in Glacier NP have stopped moving lately, and are now just permanent ice fields. Is that what you are talking about, perhaps? If so, they are not glaciers any more even if once they were. Pretty sad.
mpainter @ur momisugly 6:54 PM
“….then your referred study has used obsolete processing of the satellite data, and therefore is unreliable. ”
This conclusion is overstated. These are contemporaneous studies using different approaches that reach essentially the same result for the ice loss rate. The -142 +-49GT/year for Greenland mass loss from 1992 to 2011 from the Science study is essentially indistinguishable from -200 GT/year with no error bound shown for 2002-2010 by the Princeton group. Especially if mass loss was accelerating 1992-2002.
Both studies agree that there is no risk of catastrophic mass loss this century or next. The additional good news from these studies is that should mass loss unexpectedly accelerate, we will have plenty of warning.
LetsBeReasonable says:
November 29, 2012 at 7:21 pm
===============================
Enthalpy of fusion (rounded) 80cal/g
33x 10^7 km^3 ice on earth
Weight of ice 3×10^23g
24×10^24 calories
Now, you answer your second question for us.
RobertInAz
I do not see an equivalence between the figures of the two studies. “Essentialy indistinguishable”
Some might say that this is an overstatement.
Gymnosperm, that is indeed a lot of energy. I don’t know how to apply that figure to calculate the ‘atmospheric heating foregone’ , but I can thank the ice caps for keeping the earth cooler than it would have been otherwise. I imagine the ice caps over Greenland and Antartica will take a while to melt away completely, and I won’t be around when they finally disappear and the heat that used to go into melting them, would go towards heating the atmosphere.
That reduced rate (sea level rise of 21′ in 13,000 yrs) works out to about 4″ century. Head for the hills!
Or not.
We should also note that the Land is rising at an average of 0.3 mms/year (due to rebound from the ice ages). That means the actual sea level rise over the last 20 years relative to the Land from this glacial melt is less than one-quarter of an inch.
After reading the Supplemental, it appears this new study still has not used the more accurate GIA models for Greenland.
The authors speculate that if that were done, the mass balance numbers for Greenland would fall by about the same trend as for Antarctica, or about half.
I guess this was just step one – Greenland will still get revised down to about -80 GTs/year eventually.
http://www.sciencemag.org/content/suppl/2012/11/28/338.6111.1183.DC1/Shepherd.SM.pdf
CAN SOMEONE CONVINCE CHANNEL4 TO STOP THEIR ‘MELTING POLAR CAPS’ STORIES?
C4 editors have really swallowed the global warming lunacy and have repeated this story about 20 time this year alone.
Maybe someone here can convince them to either CHECK THEIR FACTS or just stop reporting lying propaganda as if they were scientifically accepted proofs.
See what I mean here
http://www.channel4.com/news/shrinking-ice-rapid-rate-of-polar-melt-revealed
Thursday 29 November 2012 Antarctica , World Shrinking ice: rapid rate of polar melt revealed
Tom Clarke, Science Editor
The planet’s polar ice sheets are melting three times faster than they were in the the 1990s, a 20-year study of satellite records says.
The definitive analysis of the mass of ice sheets covering Greenland and Antarctica should end decades of speculation about how much their melting may contribute to sea-level rise. The study finds their combined melting has contributed 11.1 milimetres to global sea levels since 1992.
The results come as nations meet in Doha, Qatar, for this year’s global climate change negotiations. Previous estimates of sea-level rise from melting ice date from 2004 and are highly disputed.
We can now say for sure that both Antarctica and Greenland are shrinking
– Andrew Shepherd, University of Leeds
“The measurements we had to hand then couldn’t tell us whether Antarctica in particular was growing or shrinking,” said Andrew Shepherd from the University of Leeds who led the research.
“We can now say for sure that both Antarctica and Greenland are shrinking because of the changes in climate that they’ve been exposed to.”
The researchers combined data from 10 satellites designed to measure ice thickness in different ways. Some use lasers or radar to measure the height of ice, others detect changes in gravity to “weigh” the ice lying over Greenland and Antarctica.
9,000 Lake Windermeres
They concluded Antarctica has lost around 1,320 gigatonnes of ice since 1992. Greenland, which has experienced much greater warming has lost around 2,940 gigatonnes over the same period – equivalent to more than 9,000 Lake Windemeres.
Sea level is rising for a number of different reasons – mainly as the oceans expand as they warm up due to a gradually warming planet. But the contribution of the melting ice caps now accounts for about a third of the rise, the study reveals.
Read more on global warming from Tom Clarke’s recent visit to the Arctic.
http://www.channel4.com/news/tom-clarke-in-the-arctic
The analysis doesn’t sigificantly alter previous, rather uncertain predictions, of how fast ice sheets may be melting. But to have more concrete data will now improve other scientists’ ability to forecast future melt.
“This project is a spectacular achievement,” said Richard Alley, a climate scientist at Penn State University. “The data will support essential testing of predictive models and will lead to a better understanding of how sea-level change may depend on the human decisions that influence global temperature.”
==========
Contact C4 on this page
http://www.channel4.com/news/contact-channel-4-news
or go direct to email –
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If you have a comment for the newsroom please email us at: news@channel4.com
“Both studies agree that there is no risk of catastrophic mass loss this century or next.”
No they don’t. Nobody can guarantee that so far into the future.
“The additional good news from these studies is that should mass loss unexpectedly accelerate, we will have plenty of warning.”
How so? Greenland suddenly accelerated in the 1990’s, I don’t see much advance warning there.
Doug Proctor says:
November 29, 2012 at 5:08 pm
Here is the Humidity:
Graph: Global Relative humidity 1948 – 2008
Graph: Cloud Cover at various levels and Atmospheric Water
Leif Svalgaard says this paper is wrong and the Sun’s TSI is constant.
Judithgate shows the IPCC is doing their darnest to bury any hints that the sun might be a variable star that has a major impact on climate.
However there are plenty of NASA articles that show they really do not understand just how variable the sun is.
NASA Finds Sun-Climate Connection in Old Nile Records
NASA: Quiet Sun Means Cooling of Earth’s Upper Atmosphere
NASA: Giant Breach in Earth’s Magnetic Field Discovered
NASA: SOLAR IRRADIANCE
NASA: Deep Solar Minimum
NASA: SORCE’s Solar Spectral Surprise
NASA: Solar Variability
NASA: Solar Wind Loses Power, Hits 50-year Low
EVE: Measuring the Sun’s Hidden Variability
Sasha says:
November 30, 2012 at 6:15 am
CAN SOMEONE CONVINCE CHANNEL4 TO STOP THEIR ‘MELTING POLAR CAPS’ STORIES?
…………………………
The first thing to look at is ‘Who Benefits”
You can follow the threads of who is in control and what their hidden agenda is from there.
If you want to try getting their attention about their “ME TOO” take on CAGW you can use their own words and the BBC scandal.
Surely the meltwater (at just above 0 deg C) together with the icebergs that end up in the ocean act to reduce the ocean heat content, so reducing the amount of water vapour entering the atmosphere, so reducing any supposed GHG effect in the atmosphere.
A perfect negative feedback, stable system. Or have I missed something.
And it is interesting how many AGW trolls seem to be posting on here today….
Tony, do you have some research that backs up you assertions? I cannot see the connection between ice melting and decreased evaporation when the atmospheric temperature stays constant.
Bill Illis (November 30, 2012 at 3:30 am) wrote:
“We should also note that the Land is rising at an average of 0.3 mms/year (due to rebound from the ice ages). That means the actual sea level rise over the last 20 years relative to the Land from this glacial melt is less than one-quarter of an inch.”
Bill, what is the conventional wisdom on the spatiotemporal variability of this estimate?