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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CostCo:
At December 5, 2012 at 5:26 am you say
Yes, and I would be a millionaire if I had won the Lottery. Wake me in the unlikely event that there is as sign of a problem.
And I notice that at December 5, 2012 at 5:30 am you admit you have abandoned your attempts to defend the paper by Shepherd et al.. I remind that the failure of the project reported by that paper is the subject of this thread, and your attempts to discuss other things only add emphasis to your inability to defend that paper.
Richard
CostCo says: “There are no unknown drifts that are “larger than the data” so your point is moot.”
#1) With “unknown drifts” you can not make such a claim. They are “unknown”!
#2) Drifts when combined could be. Drift A < data, Drift B Data.
So sorry, the point about Drift is relevant. If you had technical knowledge you would have already known the issues of Drift (both known and unknown), and would not have needed to ask. I suggest you go read up on Instrumentation Calibration and Drift, then take a technical course dealing with both.
CostCo says: “We have three independent techniques that see the same thing, which increases the confidence in these results a lot.”
So you claim, but that is not what the report’s Table-1 shows. I really love it when somebody makes a claim like “increases the confidence in these results a lot”. Fits right in with Al Gore and Hansen’s arm waving Sky is Falling GW press releases.
CostCo says: “Yes, but ice-loss is accelerating at a rate that is not trivial, i.e. five-fold in just 20 years.”
Five times over 20 years. Five times trivial means little to nothing. Thus Alarmism.
And once again, nothing ties supposed ice-loss to claimed AGW (claimed man-induced Global Warming due to increases in CO2). Correlation does not imply causation. But claiming it does shows proponents of GW to be intelligence challenged.
And once again, even if ice-loss was tied to CO2, we are very near the ppm level at which CO2 can have maximum impact as Greenhouse Gas. Thus further increases would be “trivial”. 😉 http://www.randombio.com/temperatures6.png
Feel free to keep commenting, but you are just reaffirming that pro-pundits of alleged AGW lack facts, don’t understand scientific method (or science), are technically weak (using computer to post on internet don’t count), mistakenly use information holed like Swiss cheese, jump to conclusions, repeat AGW talking points without verifying, and attempt to sell AGW by mass propaganda.
“richardscourtney says: And I notice that at December 5, 2012 at 5:30 am you admit you have abandoned your attempts to defend the paper by Shepherd et al.”
State your criticism please.
“richardscourtney says: CostCo: Yes, but ice-loss is accelerating at a rate that is not trivial, i.e. five-fold in just 20 years. The ice-stream acceleration has been witnessed further and further north and there’s still room for more acceleration in the coming years. A millimeter per year in sea-level from Greenland only is not that far away if acceleration continues.
Yes, and I would be a millionaire if I had won the Lottery. Wake me in the unlikely event that there is as sign of a problem.”
How is this not a sign of a problem? Do you want to see an even larger and more rapid change, like the one that is happening to the Arctic sea ice volume?
No, we don’t want to see ice loss in the Arctic. More ice loss up there (past today’s 82 north limit at minimum sea ice extents) causes more cooling.
Oh – by the way. Why has ice loss increased/continued if the earth has not warmed the last 16 years?
CostCo:
At December 5, 2012 at 7:42 am you ask me concerning the trivial rate of ice loss on Greenland
Care to run that by me again?
You are claiming some kind of problem, not me. In the event that you can think of one then tell me what it is.
And having failed in your distraction about Greenland ice loss, you now attempt to change the subject to Arctic sea ice which one can hope will provide the benefits of its total loss (but it won’t).
Instead of attempting to distract attention from the egregious Shepherd et al. paper which is the subject of this thread, how about returning to the subject of this thread or – since you admit you can’t defend the paper – going away?
Richard
“Darren Potter says: So sorry, the point about Drift is relevant. If you had technical knowledge you would have already known the issues of Drift (both known and unknown), and would not have needed to ask. I suggest you go read up on Instrumentation Calibration and Drift, then take a technical course dealing with both.”
I have technical knowledge in the satellite and instrument domains and that’s why i’m asking what drifts you are talking about. Inventing unknown & undetectable drifts is not an “argument”.
“So you claim, but that is not what the report’s Table-1 shows. I really love it when somebody makes a claim like “increases the confidence in these results a lot”. Fits right in with Al Gore and Hansen’s arm waving Sky is Falling GW press releases.”
Absolutely it increases confidence since the methods are largely independent. Imagine if we only had GRACE, then pundits could forever claim that the GIA-adjustment is flawed and we still don’t know zilch. Now it’s clear what is going on in Greenland and the data on Antarctica is getting clearer too. Current and planned satellites will make monitoring ice sheet mass balance a routine operation in the future. Stay tuned.
“RACookPE1978 says: Oh – by the way. Why has ice loss increased/continued if the earth has not warmed the last 16 years?”
The Arctic has warmed up quite a bit in the last 16 years and so has Greenland including the sub-surface waters around it.
“richardscourtney says: how about returning to the subject of this thread ”
That’s fine, so what is your criticism? Hopefully something more substantial than unknowable phantom drifts..
You are wrong. Dead wrong.
Arctic sea ice (in the summer is ONLY between 82 north and 90 north (the pole). Arctic sea ice (in the winter) is located between 70 north and 90 north.
the ONLY Arctic temperatures going higher recently are 1200 – 1600 kilometer INLAND between 60 north and 65 north. And they are going up because the CO2 increase is increasing plant growth by 22% to 27% everywhere globally, and THAT albedo change is increasing sunlight absorption and increasing INLAND temperatures above the ever-darker, ever greener tundra and forests.
The Denmark DMI daily MEASURED arctic temperatures at 80 north have NOT risen since 1958. And, recent DMI summertime measurements are actually going down as CO2 levels increase.
“RACookPE1978 says: The Denmark DMI daily MEASURED arctic temperatures at 80 north have NOT risen since 1958. And, recent DMI summertime measurements are actually going down as CO2 levels increase.”
That may be but the area above 80N is just a small part of total area of the Arctic. I haven’t chaked what ECMWF uses for it’s definition of the “Arctic” but the trend is very clear:
http://www.ecmwf.int/products/forecasts/d/inspect/catalog/research/eraclim/timon/timon_ana_2D!2T!anom!Arctic!195701-201212!/
CostCo:
At December 5, 2012 at 8:52 am you ask me
I have several criticisms but as a start I suggest that you address the issue first raised by Billy Liar in his post at December 3, 2012 at 2:13 pm and cited by me in my post at December 4, 2012 at 3:40 am.
This issue alone condemns the method adopted by Shepherd et al. to the garbage bin for the reason explicitly sated in my post at December 4, 2012 at 3:40 am.
Billy Liar posted it. I cited it as an example. You have not addressed it.
Richard
Well, since the sea ice (at minimum extents) is ONLY found between 82 north and the pole, what the temperature might be 600 km, 1200 km, and 2000 km further south won’t affect the local sea ice melt rate. The Denmark measurements are the ONLY ones at the same latitude where the sea ice is. They are the only ones that matter. Annual averaged artic temperatures – when the ice is already frozen – don’t matter either: The ice has frozen, the sun is below the horizon, and the winter sea ice extents across the arctic are the same as are they always have been recently measured.
And, since the exposed water around the melting sea ice has a thermal capacity 1000 times the thermal capacity of the air blowing past the sea ice, the surface temperatures 1200 km further south – where Hansen’s GISS plots a single red “blob” in the middle of the Canadian tundra – won’t affect water temperatures nor sea ice melt rates.
You are wrong.
In defense of the paper, my hope is that the authors believe that they have accounted for the various instrumentation errors and biases. If the instrumentation error is random and normally distributed, then it would tend to cancel out over numerous measurements. The real problem is discovery and management of biases.
What I find fascinating about the discussion is when Greenland ice loss eventually starts decelerating, the Arctic ice cap starts recovering, and sea levels stop rising then we will have equal and opposite alarmist reaction to climate change (this time cooling) with a set of solutions that looks suspiciously like those needed to address warming.
This all looks like a negative feedback to me. Trenberth’s missing heat is making its way to the arctic ocean where it melts ice and is eventually radiated into space.
CostCo says: “I have technical knowledge in the satellite and instrument domains and that’s why i’m asking what drifts you are talking about. Inventing unknown & undetectable drifts is not an “argument”.”
This coming from a person who makes vague, arm waving, unreferenced, or undefined statements like the following:
“Greenland is losing mass a lot faster than only 20 years ago and some areas in Antarctica are changing too.”
“Yes, but ice-loss is accelerating at a rate that is not trivial, i.e. five-fold in just 20 years”
“Heck, in some places and at some times the ice sheet surface is dropping 10+ meters per year!”
“I seriously doubt that it would change the GRACE-results either.”
“Subsidence of bedrock or what? Anyway, the surface velocity of the ice is known, which can be used to infer what is going on.”
Now assuming you really do have technical knowledge, then you tipped your hand to being dishonest. By denying there are unknown / undetectable drifts that cause inaccuracy in the satellites and instruments aboard the satellites, despite there being conflicting results coming from data collected from different platforms. You would also have to know there had been unknown calibration problems between satellites calibrated on the ground and then using those satellites internal temperatures for recalibration once in space. Along with unknown problems such as correcting for diurnal cycle drifts. Then there has been drift induced errors into satellites’ instruments/data collected because of human error in failing to take into consideration orbital changes. And you would have heard of drift errors due to non-linear calibration problems in at least one satellite used by AGWers. Yes, those drifts are known now, but those drifts/errors were originally unknowns or undetected.
A dishonesty that seems to permeate throughout the AGW community:
http://wattsupwiththat.com/2010/10/04/an-over-the-top-view-of-satellite-sensor-failure/
So there you go either you don’t know what your talking about and unknown & undetectable drifts is valid issue, (backed by errors in data as reported), or you are being dishonest in denying such drifts.
That item should be added to Anthony’s “Did You Know . . . ? series.
“Now assuming you really do have technical knowledge, then you tipped your hand to being dishonest. By denying there are unknown / undetectable drifts that cause inaccuracy in the satellites and instruments aboard the satellites, despite there being conflicting results coming from data collected from different platforms. You would also have to know there had been unknown calibration problems between satellites calibrated on the ground and then using those satellites internal temperatures for recalibration once in space. Along with unknown problems such as correcting for diurnal cycle drifts. Then there has been drift induced errors into satellites’ instruments/data collected because of human error in failing to take into consideration orbital changes. And you would have heard of drift errors due to non-linear calibration problems in at least one satellite used by AGWers. Yes, those drifts are known now, but those drifts/errors were originally unknowns or undetected.”
Error related to calibration are taken into account and they contribute to the error-bars. Satellite and inter-satellite calibration is a constant ongoing effort and large drifts will be caught. Basically you’re insinuating that the glaciological community as a whole does not know how to assess errors and neither does Nature/Science etc. Besides, considering the accuracy needed for sea-level estimation, the comparatively large changes in ice sheet elevation are much easier to detect.
“RobertInAz says: What I find fascinating about the discussion is when Greenland ice loss eventually starts decelerating, the Arctic ice cap starts recovering, and sea levels stop rising then we will have equal and opposite alarmist reaction to climate change (this time cooling) with a set of solutions that looks suspiciously like those needed to address warming.”
Considering the positive feedbacks associated with the loss of ice- and snow-cover during summer, it quite possible that won’t happen anytime soon. The sea ice volume is showing no signs of recovery.
“richardscourtney says: I have several criticisms but as a start I suggest that you address the issue first raised by Billy Liar in his post at December 3, 2012 at 2:13 pm and cited by me in my post at December 4, 2012 at 3:40 am.”
You must mean this: “Can somebody tell me how these satellite altimeters compensate for the inverse barometer effect where there are no measurements of the surface pressure?
In order to get accurate sea levels you have to have accurate simultaneous atmospheric pressure measurements.”
Several things come to mind:
1. I’m not aware of atmospheric-pressure trends over 20 years that could cause a bias in the barometric correction – are you? Also, are you postulating that there are localised atmospheric pressure anomalies over some areas (for example the Amundsen Sea) that causes an uncorrected bias that is the order of tens of meters? Does not sound credible to me.
2. In any case the barometric correction is relevant in the estimation of sea-level where the needed accuracy is 1-2 orders of magnitude higher than over ice sheets. If you believe that this correction is large enough to cause large uncertainties in Ice Sheet elevation-change estimates, please post some numbers.
3. Thanks to atmospheric reanalysis and planetary models the surface pressure is not “unknown” anywhere on the planet during the satellite era. Of course there are related uncertainties but please show that the errors resulting from this are relevant when retrieving relative ice sheet elevations.
4. The barometric correction is an issue in altimetry, while gravity and SAR-measurements are not affected by it. As discussed, the other independent techniques see the same signal.
CostCo:
Thankyou for your post addressed to me at December 6, 2012 at 2:05 am. This is my reply and it addresses each of your numbered points in turn.
You say and ask
Barometric pressure varies with temperature, and temperature has varied.
Sea level varies with barometric pressure.
Nobody knows how this has affected “a bias in barometric correction”, and that is my point.
Local temperature variations differ from the global variation.
Sea level rises one centimeter per millibar drop in air pressure. Strong storms can have 50 millibar drop in pressure, causing a 50 cm rise in water levels on top of levels due to wind and tides. Hence, the local maximum error from barometric pressure variation is of the order of 50 cm. The press release of the paper says
Hence, the possible local effect of barometric pressure variation on sea level is 5 times the magnitude of the claimed contribution to global sea level from Greenland ice loss over the measured period. Assume actual local effects are a tenth of the maximum, then barometric pressure variations are a significant effect on local sea level.
You say
Ice sheet measurements are not relevant. The barometric effect is on sea level. However, the sea level determinations are used to “reconcile” with ice sheet measurements.
You say
Models are assumptions and not measurements. Nobody can know the errors introduced by the assumptions. The issue is sea level determination errors. Again, variations in barometric pressure affect sea level and not ice elevation. However, the sea level determinations are used to “reconcile” with ice sheet measurements.
You say
The issue is variation in sea level induced by varying barometric pressure. Altimetry is not relevant. And you have “explained” nothing. Instead, and as is your usual practice, you have presented arm-waving assertions, irrelevancies and assumptions. The “other techniques” are not “independent”: they each utilise the same assumptions. (It seems that “independent” has a strange meaning for warmunists who claim, for example, that tree ring analyses of the same trees are “independent”.)
The effects of barometric pressure changes are not known. And those effects could be the cause of most of the apparent increase to sea level distant from shores which is responsible for most of the claimed increase to sea level change. If so, then the system reported by Shepherd et al. is useless as an indicator of sea level rise near shores because a change to distribution of barometric pressure changes would have severe effects on sea level near shores. Indeed, such an effect on sea level at shores would be much more rapid (although not permanent) than ice loss.
Also, without knowledge of the barometric effects on sea level any claim that the sea level determinations “reconcile” with ice changes are speculative at best and probably indicate confirmation bias.
Richard
“richardscourtney says: Ice sheet measurements are not relevant. ”
You seem to have a fundamental misunderstanding about what was measured and estimated in Shepherd et. al. This study did not measure sea-level anywhere! Instead, Ice Sheet mass-balance was estimated over a period of 20 years. The mass-gain/loss in the Ice Sheets was converted to sea-level-equivalent with a simple formula.
Do you have any criticism on the scientific content of Shepherd et. al., i.e. on Ice Sheet mass-balance estimation using the three (largely) independent spaceborne techniques?
CostCo:
re your post at December 6, 2012 at 7:27 am.
Firstly, let me apologise for an error. As you infer, I did misread the above article in that I (mis)understood the JPL work to have been incorporated in the paper by Shepherd et al.
Mea culpa
My error does make my answers to your points misplaced (although true with respect to the JPL work). And, therefore, several of my answers to your points are inappropriate. Please understand that this was a genuine mistake and not an attempt to avoid your points nor to misrepresent them. I apologise for any offence my error has caused.
I reply to your specific question asking
I do not agree that the methods are “largely independent”. This is one of the issues which my error did not distort. The techniques each use the same assumptions and there is no available independent calibration. Hence, the techniques have unknown – but probably similar – errors (the “drift” issue being one such unquantifiable error).
And this raises the ‘TRF issue’. Without a static terrestrial reference the ‘differences’ in ice height could be artifacts of the variation in TRF and there is no way to determine to what degree this is the case.
Richard
Richard: As explained by me in this thread, the TRF-error is way too small to cause any issues in ice sheet elevation measurements. It is relevant for sea-level where millimetric accuracy and stability is required over long periods of time.
The techniques are really “largely independent” bacause the measurement-principles are so different (measuring gravity, measuring height, measuring surface-movement). “Drifts” are measured continuously in satellite cal&val activities so the existence of them is known. This is why the existence of the sub-millimeter TRF-error is known. I cannot comment on gravity but I fail to see how SAR or altimetry could have unknown large drifts.
There is another dimension to establishing a reliable TRF that must not be overlooked – the undulation of the geoid we call Earth. Its shape is affected by internal phenomena (that we attempt to measure as gravimetrics) resulting in minor flexing of the crust that (due to elasticity of material) not always results in earthquakes. The wide varieties of factors like erosion deposits, variations in barometric pressure and salinity at any point on any given day all contribute to the enormous complexity of any valid mathematical solution. Has anyone presented good data showing that the current gravimetric method used by satellites actually has a resolution below centimeters ? This takes us back to one of the points in this article – that we have nothing without a good baseline, making arguments over millimeters sound truly absurd.
References:
http://kartoweb.itc.nl/geometrics/reference%20surfaces/body.htm
http://en.wikipedia.org/wiki/Geoid
http://en.wikipedia.org/wiki/Mantle_%28geology%29