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 says: “You guys are deluded if you imagine the TRF-uncertainty is big enough to change the current trend to an “opposite trend”. ”
What is deluded is those who assume that even if there is ice loss and a rise in sea levels, that it proves “Anthropological” global warming. All the claimed ice lose and rise in sea levels proves is Earth’s climate is undergoing a change, like previous changes in Earth’s climate long before man.
“REPLY: “…to see what is really happening.” Agreed, they simply don’t know. This paper is just another guess based on noisy data, and having a stable baseline is key to that. There’s no getting around the need for a stable baseline – Anthony”
It’s not a “guess”, but the best available multi-satellite estimate with quantified error-bounds. The TRF-error can influence sea-level measurements there the trend is few mm. per year but the ice sheet surface rises and falls orders of magnitude more per year and makes a 0.45mm/year uncertainty negligible. Heck, in some places and at some times the ice sheet surface is dropping 10+ meters per year!
Another example of how the moddlers use the Press Release to gather publicity for what ever it is they are pushing today. We expect that from politicians, religious leaders, soap and auto makers not from reputable scientists.
hum modelers is correct but perhaps moddlers should have been muddlers!
“REPLY: and if that were fully true, then they wouldn’t need to push for a new space platform and mission to correct the problem. Bottom line is we don’t know. All we have are estimates based on noisy data. If this were a skeptical paper, such things would be demanded, as it stands you give this paper a free pass, part of the problem with government funded group think of which you are a part. – Anthony”
The TRF-error and it’s maximum magnitude are known, not unknown. A more stable coordinate-system is required to reduce the error on sea-level trends that are of the order of 3mm/year, so 0.45mm/year is a considerable uncertainty. Over ice-sheets the TRF-error is negligible and certainly does not change the results.
The bottom line is that three largely independent techniques see the same signal. Greenland is losing mass a lot faster than only 20 years ago and some areas in Antarctica are changing too. There are the facts, causes can be debated until the cows come home but the fact remains that ice is being lost at an accelerating pace.
When I saw the errors: “….–142 ± 49, +14 ± 43, –65 ± 26, and –20 ± 14 gigatonnes year−1….” it blew my mind. How do you draw meaningful conclusions when the errors are that large?
We now have more accurate measurements of a bee’s digit.
I love the sentence. 😛 Specially during this century, when temperatures hasn´t changed a lil bit.
@CostCo says: 8:30 am:
there are zero tide-gauges in the open ocean, where incidentally much of the largest sea-level changes [verified how?, by what independent measurements?] have happened…..
Tide-gauges and satellite-data agree where they can be compared.
Then SHOW THE COMPARISON. Tide gauges were apparently good enough before altimetry data existed. Failure to continue the plot of the tidal gauge record only invites, nay demands, suspicion.
From the 23 stabel sites selected by Douglas in 1997, we get a sea level rise of about 1.4 mm per year measured over 200 years:
(From Wiki:,,, sorry! …. but I have seen the 1.4 mm fromm this study quoted elsewhere… bear in mind recent research shows groundwater extraction may contribute between 0.6 and 0.7 mm of that…
Original data for this figure is from the Permanent Service for Mean Sea Level [2] (PSMSL). Douglas (1997), defined the following criteria for selecting records from the PSMSL which were long, reliable, and avoided large vertical geologic changes:
1. Each record should be at least 60 years in length
2. Not be located at collisional plate boundaries
3. At least 80% complete
4. Show reasonable agreement at low frequencies with nearby gauges sampling the same water mass
5. Not be located in regions subject to large post-glacial rebound
Funny how previously all our scientific measures could be added up with great certainty to explain sea level rises of far great magnitude than that discussed here, and people went searching for and found “missing heat” …Then along came the groundwater guys who threw a small spanner in the works…but now we revise everything again and somehow it still all “adds up”.
Why is it that logic and ocean levels do not mix ?
(ref. Pacific Ocean Google search )
the Pacific Ocean is 165,200,000 square km, or 64.1 million square miles
1/3 of the worlds surface
1/2 of the worlds water
and the doctors with degrees in stupid say that they can measure not only this but the other half to 0.01mm ? ( 11.1 mm rise since 1992 )
How I ask do you calculate to 0.1 mm the moon affect ?
How do you calculate to 11.0 mm weather, 64 million square miles, flying from Hawaii to New Zealand takes a day out of your life and under you is only water !
in a class of 27, 14-15 year old’s only 8 could measure exactly how deep the water was in a 2 gallon bucket !
Actually its worse than we thought.!!
We now have accurate measurements of a bee’s digit
But nobody bother to calibrate our ruler. !
Billy Liar says:
December 3, 2012 at 9:03 am
“You failed to point out that the Northern hemisphere snow cover low record was for the month of June and the record is only 45 years long. Maybe Eurasia is having a drought? They make no statement about the rate of change of annual precipitation in the relevant area – I wonder if that’s reducing too?”
Quite, Such basic questions should at least be considered and checked for by an honest scientists and addressed in the conclusion, I wonder if they are in the full paper?
Stephen Rasey says: December 3, 2012 at 8:25 am
“….Does anyone have a quick conversion factor between 100 Gt water = X mm Sea Level @ur momisugly 4 deg C ?…..”
This may help – ice, not water….
From Zwally etal 2011: 31 Gt ice loss per year from Antarctica is equivalent to +0.1 mm SLE (Sea Level Equation ??)
http://icesat4.gsfc.nasa.gov/cryo_data/publications/Zwally-Giovinetto_SurveysInGeophysics_2011-1.pdf
REPLY: and if that were fully true, then they wouldn’t need to push for a new space platform and mission to correct the problem. Bottom line is we don’t know. All we have are estimates based on noisy data. If this were a skeptical paper, such things would be demanded, as it stands you give this paper a free pass, part of the problem with government funded group think of which you are a part. – Anthony
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According to JPL the TRF-related uncertainty is 0.45mm/year. The need for a new platform is driven by the desire to improve this. It is true that all we have are estimates based on noisy data. This is true for every measurement made in science. There is always noise. there is no getting rid of noise, no “stable baseline”. The question is how good ( uncertain) is the estimate? In the case of TRF it is good, but it can be better. Of course one can always spin the improvement of a process as an admission that it is all horribly wrong and highly uncertain. But looking at the actual numbers, one can see it for what it is. A good improvement to an already accurate system. All measurement is wrong. The issue is relative wrongness. All raw data is wrong. The issue is how wrong. So the “problem” of uncertainty will always be with us. There is no “correcting the problem.” There is only decreasing the uncertainty. You tend to frame this as if uncertainty in TRF renders all measurement useless. It doesn’t. There is now and will forever be an uncertainty in TRF. GRASP narrows that uncertainty it does not eliminate it. So for example, you wrote
“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.”
The total uncertainty is .6mm/year. Of that .45mm/year is related to TRF. The noise in TRF
does not “put” “measurement systems into uncertainty” . All measurement has uncertainty. No science is settled. The “no spin” way to express this is : The uncertainty ( .6mm) is composed of TRF uncertainty. TRF uncertainty is a large component of the uncertainty. When the TRF uncertainty is reduced ( not eliminated ) by GRASP, the total uncertainty will be reduced. The TRF issue will never be “resolved” , the accuracy will be improved.
REPLY: And yet, they still didn’t take this into account. I find it gobsmacking that people at JPL don’t talk to one another, or that 47 scientists couldn’t/wouldn’t bring this issue to bear. Until the baseline is established, the measurements are in fact uncertain with a noise component. We don’t know what the true noise component is, all we have are estimates. And, we won’t know what the true magnitude is until such time that a stable baseline is established. I think all that hanging around the BEST folks has turned into a warmist. You talk like Rhodes now. – Anthony
All I know is that crocodiles swam in the arctic region many, many, many, many, moons ago, the Russians were using the NE Arctic passage commercially from the 1930’s onwards and underneath from Greenland to Siberia is a long line of Volcanoes that erupted a decade or so ago.
Any such paper that does not account for the uncertainty in Terrestrial Reference Frame is being knowingly and intentionally untruthful and misleading.
This is by far the biggest uncertainty in interpreting this kind of data and is known to be a major problem. This cannot have been “overlooked” by 49 different professional scientists.
The publishing of this paper seems to have been orchestrated to coincide with the beginning of COP18 in Doha. This yet more politics masquerading as science, which comes as no surprise when seeing Andrew Shepherd as a lead author.
kevin Kinser writes:
“My understanding of the significance, though, is that despite the uncertainty with any individual measurement, the combination of multiple sources reveals a common pattern.”
To get that result, you have to assume that the errors cancel one another. Real scientists do not make such assumptions but prove that the errors cancel one another. Does Shepherd’s paper provide such proofs?
If there’s ice loss in Antarctica, that doesn’t mean it’s melting–i.e., it’s not a proxy for global warming. It never gets above freezing there (except on the Peninsula). Ice will decline there, and in Greenland, if days are less cloudy than previously (= more sunlight), if the humidity is lower, if the wind is greater, and if snowfall declines. Sunnier, dryer, and windier days increase sublimation (evaporation w/o melting). Lower precipitation creates a net loss from year to year.
Another cause could be speedier glacier movement–which again isn’t a proxy for warmer weather. Glaciers move more quickly when there’s more weight accumulated at their upper ends from snowfall exceeding sublimation, and when obstacles t their lower ends are removed, such as when the end of a grounded glacier breaks off and becomes sea ice. These are random events, mostly.
(Right?)
Why does anyone with an understanding of this global warming business tout NASA as if it were a reliable source of data and science? Why praise it as a performer of heroic feats? It seems foolish and self-defeating, if you are a skeptic, to advertise NASA as a national shrine. With such praise, you confirm NASA in its course. To get them to change, you have to change public attitudes toward this agency. When a bee stings you,it has your attention,does it not? Same principle, wise up.
Beyond the issue with the satellite data and the non compliance with tide gauge measurements, there is more to put this into perspective:
Ice sheets have been melting most of the time since the last ice age. This is what would be expected.
There is nothing to see in Antarctica, (except increasing sea ice).
Greenland temperatures have just recaptured 1940s temperatures following the cyclic of AMO Once AMO turns negative in a couple of years, Greenland temperatures will follow.
Houston and Dean (2011) use more robust but not so fancy tide gauge data and conclude the OPPOSITE:
“Our analyses do not indicate acceleration in sea level in U.S. tide gauge records during the 20th century. Instead, for each time period we consider, the records show small decelerations
that are consistent with a number of earlier studies of worldwide-gauge records.”
http://www.jcronline.org/doi/pdf/10.2112/JCOASTRES-D-10-00157.1
CostCo says:
>>
Stephen Rasey, there are zero tide-gauges in the open ocean, where incidentally much of the largest sea-level changes have happened.Tide-gauges and satellite-data agree where they can be compared.
>>
And that doesn’t strike you as being problematic ??
It’s not that the satellites “agree” with tide gauges like it confirms they are correct to start with, they are explicitly and intentionally adjusted to be the same as tide gauges measurements. This is part of the calibration process. This says not more than they are _made_ to be the same.
Now the idea that all this (alleged) melt water is somehow choosing to pile up in the middle of the oceans where we have no means of checking its level seems a little odd without some solid theoretical reason why it should pile up where we can”t check it.
” Referring to the satellite time-series is a much more comprehensive measurement of global sea level. ”
More comprehensive cover does not mean it better, more accurate or worth believing. That needs to be established independently. Once that has been done, the more comprehensive coverage will be a distinct bonus.
For now that is not the case.
There is a much more obvious and likely conclusion to noting that the water is piling up in the middle of the ocean: the interpretations of the raw satellite data are consistently and seriously over-estimating the rise is sea level.
In fact this is precisely what was already established by JPL in the GRASP proposal.
“P. Solar says:
December 3, 2012 at 10:28 am
Any such paper that does not account for the uncertainty in Terrestrial Reference Frame is being knowingly and intentionally untruthful and misleading.”
That’s complete BS, please educate yourself. 0.45mm/year uncertainty is negligible compared with ice sheet elevation changes.
“This is by far the biggest uncertainty in interpreting this kind of data and is known to be a major problem. This cannot have been “overlooked” by 49 different professional scientists.”
It isn’t “overlooked”, you’re just wrong, see above for details.
Can I ask 2 silly/simple questions?
1) What are the error bands? 2 sigma? 1 sigma? Assuming what probability distribution? What was taken into account when calculating these errors? What wasn’t?
(I don’t have access to the original paper, even assuming the information is in there.)
2) No one has answered the question as to what the tidal gauges have been showing since the second half of the graph has been added. I know I’m a grumpy old cynic but this looks rather like a hockey stick again with two different merthods tagged together:
The price of apples went up by a certain amount over a 10 year period. But the price of oranges has gone up three times faster in the 10 years since then …