There’s a paper (Shepherd et al) on ice loss and sea level rise that has been making the rounds in media (such as this article in Science Recorder, claiming it validates global warming) that is causing some stir, mainly because it has a powerfully written press release combined with a volume of researchers (47 scientists), plus additional never before used together satellite data, because more data and more scientists is always better, right?
Here’s the press release where they claim to have “clear evidence”. A deconstruction follows using NASA JPL’s own internal program documents showing that the “certainty” claimed in Shepherd et al really falls apart for lack of a stable reference for the data.
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From the University of Leeds
Clearest evidence yet of polar ice losses
International satellite experts release definitive record of ice sheet changes
An international team of satellite experts has produced the most accurate assessment of ice losses from Antarctica and Greenland to date, ending 20-years of uncertainty.
In a landmark study, published on 30 November in the journal Science, the researchers show that melting of the Antarctic and Greenland ice sheets has contributed 11.1 millimetres to global sea levels since 1992. This amounts to one fifth of all sea level rise over the survey period.
About two thirds of the ice loss was from Greenland, and the remainder was from Antarctica.
Although the ice sheet losses fall within the range reported by the IPCC in 2007, the spread of the IPCC estimate was so broad that it was not clear whether
Antarctica was growing or shrinking. The new estimates are a vast improvement (more than twice as accurate) thanks to the inclusion of more satellite data, and confirm that both Antarctica and Greenland are losing ice.
The study also shows that the combined rate of ice sheet melting has increased over time and, altogether, Greenland and Antarctica are now losing more than three times as much ice (equivalent to 0.95 mm of sea level rise per year) as they were in the 1990s (equivalent to 0.27 mm of sea level rise per year). The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE) is a collaboration between 47 researchers from 26 laboratories, and was supported by the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA).
Led by Professor Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA’s Jet Propulsion Laboratory, the study combines observations from 10 different satellite missions to develop the first consistent measurement of polar ice sheet changes.
The researchers were able to reconcile the differences between dozens of earlier ice sheet studies through careful use of matching time periods and survey areas, and by combining measurements collected by different types of satellites.
Professor Shepherd, who coordinated the study, said: “The success of this venture is due to the cooperation of the international scientific community, and due to the provision of precise satellite sensors by our space agencies. Without these efforts, we would not be in a position to tell people with confidence how the
Earth’s ice sheets have changed, and to end the uncertainty that has existed for many years.” The study also found differences in the pace of change at each pole.
Dr Ivins, who also coordinated the project, said: “The rate of ice loss from Greenland has increased almost five-fold since the mid-1990s. In contrast, while the regional changes in Antarctic ice over time are sometimes quite striking, the overall balance has remained fairly constant – at least within the certainty of the satellite measurements we have to hand.”
Commenting on the findings, Professor Richard Alley, a climate scientist at Penn State University who was not involved in the study, said: “This project is a spectacular achievement. 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 temperatures.”
‘A reconciled estimate of ice sheet mass balance’ by Prof Shepherd et al is published in Science on 30 November 2012, DOI: 10.1126/science.1228102.
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All well and good, and it looks like a home run for Professor Andrew Shepherd at the University of Leeds and Dr Erik Ivins at NASA’s Jet Propulsion Laboratory and the team of 45 others if you just read the press release. But, let’s look a bit deeper, the paper abstract reads:
A Reconciled Estimate of Ice-Sheet Mass Balance
Abstract
We combined an ensemble of satellite altimetry, interferometry, and gravimetry data sets using common geographical regions, time intervals, and models of surface mass balance and glacial isostatic adjustment to estimate the mass balance of Earth’s polar ice sheets. We find that there is good agreement between different satellite methods—especially in Greenland and West Antarctica—and that combining satellite data sets leads to greater certainty. Between 1992 and 2011, the ice sheets of Greenland, East Antarctica, West Antarctica, and the Antarctic Peninsula changed in mass by –142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year−1, respectively. Since 1992, the polar ice sheets have contributed, on average, 0.59 ± 0.20 millimeter year−1 to the rate of global sea-level rise.
Note the key words here “satellite altimetry, interferometry, and gravimetry data sets” along with the second named author “Dr Ivins, who also coordinated the project…at NASA’s Jet Propulsion Laboratory”
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Hold that thought about the key words, and now read this, excerpted from our previous report: Finally: JPL intends to get a GRASP on accurate sea level and ice measurements
New proposal from NASA JPL admits to “spurious” errors in current satellite based sea level and ice altimetry, calls for new space platform to fix the problem.
This recent internal PowerPoint presentation (obtained from an insider) from NASA JPL touts the new GRASP (Geodetic Reference Antenna in Space) satellite project. I’d say it is more than a bit of a bombshell because the whole purpose of this new mission is to “fix” other mission data that apparently never had a stable enough reference for the measurements being made. This promises to rewrite what we know about sea level rise and acceleration, ice extent and ice volume loss measured from space.
What is most interesting, is the admissions of the current state of space based sea level altimetry in the science goals page of the presentation, as shown in the “Key science goals” slide:
The difference between tide gauge data and space based data is over 100% in the left graph, 1.5 mm/yr versus 3.2mm/yr. Of course those who claim that sea level rise is accelerating accept this data without question, but obviously one of the two data sets (or possibly both) is not representative of reality, and JPL’s GRASP team aims to fix this problem they have identified:
TRF errors readily manifest as spurious sea level rise accelerations
That’s a bucket of cold water reality into the face of the current view of sea level rise. It puts this well-known and often cited graph on Sea Level Rise from the University of Colorado (and the rate of 3.1 mm/yr) into question:
What’s a TRF error? That stands for Terrestrial Reference Frame, which is basically saying that errors in determining the benchmark are messing up the survey. In land based geodesy terms, say if somebody messed with the USGS benchmark elevation data from Mt. Diablo California on a regular basis, and the elevation of that benchmark kept changing in the data set, then all measurements referencing that benchmark would be off as well.
In the case of radio altimetry from space, such measurements are extremely dependent on errors related to how radio signals are propagated through the ionosphere. Things like Faraday rotation, refraction, and other propagation issues can skew the signal during transit, and if not properly corrected for, especially over the long-term, it can introduce a spurious signal in all sorts of data derived from it. In fact, the mission summary shows that it will affect satellite derived data for sea level, ice loss, and ice volume in GRACE gravity measurements:
That list of satellites, TOPEX, JASON 1-3, ICESAT1-2, and GRACE 1-2 pretty much represent all of the satellite data used in the new Shepard et al study released this week A Reconciled Estimate of Ice-Sheet Mass Balance.
In a nutshell, other JPL scientists (Yoaz Bar-Sever, R. Steven Nerem, and the GRASP Team) are saying we don’t have an accurate reference point for the satellites, and therefore the data from these previous satellite missions likely has TRF data uncertainties embedded. They say clearly in their PowerPoint presentation that:
The TRF underlies all Measurement of the Earth
And, most importantly, they call for a new space program, GRASP, to fix the problem.
Without that stable Terrestrial Reference Frame that puts the precision of the baseline satellite measurements well below the noise in the data, meaning all we have are broader uncertain measurements. That’s why the plan is to provide ground based points of reference, something our current satellite systems don’t have:
To help understand the items in the side panels:
GNSS = Global Navigation Satellite System – more here
SLR = Satellite Laser Ranging – more here
DORIS = Doppler Orbitography and Radiopositioning Integrated by Satellite – more here
VLBI = Very Long Baseline Interferometry – more here
Taken together, these systems will improve the accuracy of the TRF, and thus the data. It’s rather amazing that the baseline accuracy didn’t come first, because this now puts all these other space based measurement systems into uncertainty until their TRF issues are resolved, and that’s an inconvenient truth.
We’ll never look at satellite based sea level data or GRACE ice volume data in quite the same way again until this is resolved.
See the JPL PowerPoint here: Poland 2012 – P09 Bar-Sever PR51 (PDF)
Summary:
1. JPL admits that satellite measurement of the Earth has issues because a stable Terrestrial Reference Frame was never established for any of the satellite programs. It’s like setting out to do a terrestrial survey without having an accurate benchmark first. This puts all subsequent data derived with the stable benchmark (the stable TRF) into question.
2. The lack of a stable TRF affects most if not all satellite programs used in this new Shepherd et al paper ‘A reconciled estimate of ice sheet mass balance‘ including ICESAT and GRACE, upon which the paper heavily relies.
3. In searching both the full paper (which I purchased from AAAS) and from the extensive supplementary materials and information (SM-SI available here: Shepherd.SM-SI.pdf ) for Shepherd et al, I find no mention of TRF or “Terrestrial Reference Frame” anywhere. It appears that all 47 authors are unaware of the TRF stability issue, or if they were aware, it was never brought to bear in peer review to test the veracity of the paper and its conclusions from the satellite data. Section 3 of the Shepard et al SM-SI deals with uncertainty, but also makes no mention of the TRF issue.
4. The lack of a stable TRF puts all of the space based geodetic data into question, thus the conclusions of the Shepherd et al paper are essentially worthless at the moment, since there isn’t any good way to remove the TRF error from the data with post processing. If there were, the GRASP team at NASA JPL wouldn’t be calling for a new satellite platform and mission to solve the problem. Obviously, this isn’t an issue they take lightly.
In my opinion, the folks at NASA JPL really should get those two teams talking to one another to get a handle on their data before they make grand announcements saying :
An international team of satellite experts has produced the most accurate assessment of ice losses from Antarctica and Greenland to date, ending 20-years of uncertainty.
A good first step would be to get the GRASP mission funded and then go back and redo Shepherd et al to see if it holds up. Until then, it’s just noisy uncertain data.
UPDATE: Figure 4 in the Shepherd et al paper shows clearly how uncertain the GRACE and other data is. They used a brief bit of Laser Altimetry data, shown in green. Laser Altimetry is more accurate that the radar/microwave based data from the other satellite platforms, and is one of the keystones specified for the proposed GRASP mission to clean up the noisy radar/microwave based data.
Note that the Laser Altimetry data in green is essentially flat across the short period where it is included in all four panels, though there is a slight drop in Greenland, but the period is too short to be meaningful.
The uncertainty is quite clear in Table 1, which has error ranges larger than the data in some cases:
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The TRF should have been sorted first but perhaps 30 odd years ago the technology was not there. But hey, stable door and bolted horse comes to mind.
Dude! It needs a fold!
see http://theresilientearth.com/?q=content/new-ice-surveys-finds-slower-ice-sheet-melting
for a critique of this ‘paper’
That’s Shepherd, not Shepard.
I was at the panel discussion where he unveiled this a number of weeks ago.
http://tallbloke.wordpress.com/2012/11/02/jonathan-porrit-repositioning-the-climate-change-debate/
REPLY: Fixed thanks – Anthony
This is how they work!
You have to check everything they claim, and you get just as dissapointed everytime how they fudge the numbers makes cliams out of clean air or from pure data noise. They trade no significant trend eith konsensus instead. But they cant no more get a way with thier tricks becdause we have not only catsched up with them we are in front of them when it comes to facts datat and the science. They are corrupted with the “cause”.
I’ve been waiting all weekend for your take on the Shepherd paper [note correct spelling of author’s name]. My understanding of the significance, though, is that despite the uncertainty with any individual measurement, the combination of multiple sources reveals a common pattern. Sort of like Nate Silver projection the election, we can be pretty confident that the ice is really melting even in the Antarctic. Not implying you are trying to unskew the pols, of course, but not sure if your critique is suggesting that underlying reality is suspect because of uncertainty or if you just want more certainty.
Even if the paper was completely accurate it attributes 11mm of sea level rise over the last 20 years to ice loss according to the BBC coverage. That is 55mm per century. And we know that infrared does not heat the oceans, only sunlight can penetrate deeply enough to make a significant impact on ocean temperature and cause expansion. So surely this renders sea level rise a non-threat due to climate change.
So what? The paper has been printed and it is official and if it is not factual does not matter one bit to the climate warming crowd. They will refer to this often and our politicians will use this sort of thing to obtain more of our hard earned money through some type of carbon scheme. It never ends because of the power and money involved- not the science.
They don’t need to get a handle on the data. The mission was to get this headline regurgitated by the MSM while Doha was still in progress. Mission accomplished. MSNBC, NBC, Washington Post, BBC, CBS, the NYT, the Professor and Mary Ann acted as one to plant this seed in the minds of all low-information voters out there.
Saw an article about this in the loss-making Guardian. Damian Carrington was spinning like crazy.
(http://www.guardian.co.uk/environment/2012/nov/29/greenland-antarctica-4-trillion-tonnes-ice)
So it’s down to shifting goal-posts, that makes sense.
“The Ice Sheet Mass Balance Inter-comparison Exercise (IMBIE)” Oh boy! Another “Desert Storm” for the Climate Military! Sounds better than “General Relativity”, huh? More picking of fly poo out of black pepper. The mass balance comes from managing the crop of 47 scientists who had to cram their ideas into this little conflab. More ideas are better, aren’t they?
The absence of a TRF is interesting…glaringly so…if one considers that the entire climate change ball of wax relies on some arbitrary ‘normal’ sea level/temperature condition in order to define the change from that reference. Please, somebody, answer me this: Who decided that reference point? And if your data is essentially uncalibrated to any geodetic standard, how do you expect me to ‘believe’ any of this? Because that’s what it boils down to here. I am to believe that a gob of scientists wrote a paper in which NONE of the gob paused to consider simple calibration? Uh, WTF?
The full article is showing on the front page instead of the usual excerpt. Intentional?
Isn’t this U. of Leeds paper also undercut by the paper reported in the Nov. 29 WUWT thread, http://wattsupwiththat.com/2012/11/29/more-on-noisy-data-from-grace/ ?
Also, don’t these papers undermine this Leeds paper?
more data and more scientists is always better, right?
I think I’ll defer to Willis’ take on a paper’s validity being inversely proportional to the numbers of authors.
Well, at least the GRASP team is trying to get a grip…
@- “A good first step would be to get the GRASP mission funded and then go back and redo Shepard et al to see if it holds up. Until then, it’s just noisy uncertain data.”
Wrong.
The TRF may have uncertainties and errors but this does not translate into any data derived from it being ‘just’ noisy and uncertain. The magnitude of uncertainty matters, it is not a simple binary all or nothing situation. The error range is well defined and that enables any data that uses TRF to be accurately measured to a certain error range. That does NOT invalidate or refute any and all data from these sources, merely puts a limit on their error range. It is simplistic and egregious to use the residual small uncertainty in the TRF to try and reject all the improvements in the measurements of the exceptional increase in ice melt which are in any case measurede by methods that do not rely on TRF as well.
That provides a constraint on how far in error the TRF might be as the data that depend on it are confirmed by data that does not.
In addition to Anthony’s comments.
The Supplemental to the paper says the Greenland mass balance numbers were calculated using the old Peltier ICE-5G VM2 glacial isostatic model.
http://www.ualberta.ca/~dumberry/geoph440/papers/peltier_areaps04.pdf
The Antarctic mass balance and sea level contribution rates were calculated using the newer more accurate W12A and IJ05-R2 glacial isostatic models which make greater use of actual GPS measurements and better timelines on ice-sheet melt as the ice age was ending (in addition to resulting in lower overall glacier growth in Antarctica during the ice ages).
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-246X.2012.05557.x/abstract;jsessionid=B5BDF07602293FAF9C48F94EDA9FB340.d03t01
http://www.geology.cwu.edu/facstaff/tim/g501/pdf/Ivins%26James2005.pdf
The newer glacial isostatic models cut Antarctica’s mass balance losses in half versus Peltier’s ICE-5G VM2 model. So when applied to Greenland, it is expected that the same trend (50% lower) would result.
This puts the sea level contributions much lower as well. The sea level budget will then be far off what is built into the satellite estimates and the assumptions will have to be lowered.
GRACE seems to be the best we have, but it was soon discovered to have flaws – hence the need for the proposed GRASP mission:
From http://ilrs.gsfc.nasa.gov/docs/GRASP_COSPAR_paper.pdf
GEODETIC REFERENCE ANTENNA IN SPACE (GRASP) – A MISSION TO ENHANCE SPACE-BASED GEODESY
Yoaz Bar-Sever (1), Bruce Haines (1), Willy Bertiger(1), Shailen Desai(1), Sien Wu (1)
(1) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, U.S.A
It sure sounds complex deriving that TRF:
Anthony, 7th line up from the bottom, There’s an extra “really” and “tow” should be two.
REPLY: Fixed thanks – Anthony
Correct me if I am wrong, but even if in an absolute sense the reference value would be incorrect, then still the SLOPE in the period after 1990 would be the same, isn’t it? In other words, the reference value for the satellite data does not change the conclusion that the rate of sea level increase was higher in recent years.
I worked at JPL for two years when I was in college. They had some good people but like any organization, just one of of 50 people in any room really did the heavy lifting. Its annoying that a place that does really good space based sensing would make a rookie mistake like this.
And this paper made the BBC 10 o’clock news last Thursday and a write-up on the BBC website. Pure coincidence that it was aired by the BBC on the same day the govmunt announced its energy bill.
There is an explanation why this paper came into being. With 47 authors and the volume of satellite data, the Shepherd et al study had been in the works long before mention of the GRASP proposal. Remember, these guys have to buy the satellite data, too! (Having already received a grant for the work, etc. etc.). No mention of TRF also is deliberate, but just in case a reader is thinking about TRF, they protesteth too much about how carefully they matched times and places for the data points and used the whole basket of satellites in a collaboratative way.
(Not) off topic:
Why is it that while Europe, from Britain to Siberia down to Spain and Portugal and Italy have been taken over by snowstorms and near record cold we do not hear anything form the MSM?