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jr47

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NASA: Antarctic Ice Sheet gaining mass?
« on: October 31, 2015, 10:09:11 PM »
http://www.nasa.gov/feature/goddard/nasa-study-mass-gains-of-antarctic-ice-sheet-greater-than-losses

Saw this today. A longstanding widely held notion that the Antarctic Ice Sheet has been losing Gt of ice mass annually seems to be  not quite correct ,if this NASA study stands up to scrutiny.
« Last Edit: November 01, 2015, 12:55:24 AM by jr47 »

Neven

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #1 on: October 31, 2015, 11:04:17 PM »
Could you please do more than just dump a link, like copypasting the intro or parts of the text, and/or give your opinion on the matter?

BTW, I thought Jay Zwally was part of the great CAGW conspiracy, as he said Arctic sea ice would be gone by now.
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jr47

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #2 on: November 01, 2015, 12:56:27 AM »
Thanks for that Neven.
I don't 'get' the other stuff however.
????

AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #3 on: November 01, 2015, 01:02:12 AM »
For what it is worth:

The linked reference presents new research indicating that Antarctica has recently (circa 1992 to 2008) been gaining ice mass (rather than losing it as most other recent research has indicated), due to greater than expected ice mass gain in East Antarctica and the interior of the WAIS, as the research does validate the relatively high ice mass loss rates from key marine glaciers in West Antarctica.  As the rate of rise of sea level is relatively well known, if true, this research indicates that some other source of sea level rise is greater than previously thought.  Furthermore, it is possible that the reported behavior may be accounted for by outlier snow fall events like atmospheric river events, and may not fully represent long-term trends:

Zwally, H. Jay Li, Jun; Robbins, John W. Saba, Jack L.; Yi, Donghui; Brenner, Anita C. (2015), "Mass gains of the Antarctic ice sheet exceed losses", Journal of Glaciology, DOI: http://dx.doi.org/10.3189/2015JoG15J071


http://www.ingentaconnect.com/content/igsoc/jog/pre-prints/content-ings_jog_15j071


Abstract: "Mass changes of the Antarctic ice sheet impact sea-level rise as climate changes, but recent rates have been uncertain. Ice, Cloud and land Elevation Satellite (ICESat) data (2003–08) show mass gains from snow accumulation exceeded discharge losses by 82 ± 25 Gt a–1, reducing global sea-level rise by 0.23 mm a–1. European Remote-sensing Satellite (ERS) data (1992–2001) give a similar gain of 112 ± 61 Gt a–1. Gains of 136 Gt a–1 in East Antarctica (EA) and 72 Gt a–1 in four drainage systems (WA2) in West Antarctic (WA) exceed losses of 97 Gt a–1 from three coastal drainage systems (WA1) and 29 Gt a–1 from the Antarctic Peninsula (AP). EA dynamic thickening of 147 Gt a–1 is a continuing response to increased accumulation (>50%) since the early Holocene. Recent accumulation loss of 11 Gt a–1 in EA indicates thickening is not from contemporaneous snowfall increases. Similarly, the WA2 gain is mainly (60 Gt a–1) dynamic thickening. In WA1 and the AP, increased losses of 66 ± 16 Gt a–1 from increased dynamic thinning from accelerating glaciers are 50% offset by greater WA snowfall. The decadal increase in dynamic thinning in WA1 and the AP is approximately one-third of the long-term dynamic thickening in EA and WA2, which should buffer additional dynamic thinning for decades."

See also:
http://www.upi.com/Science_News/2015/10/31/NASA-study-Net-gains-for-Antarctic-ice-sheets/9711446321864/

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Csnavywx

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #4 on: November 01, 2015, 02:52:39 AM »
Interesting. Where's the now "stranded" 0.5mm/yr coming from then? Greenland and mountain glaciers? That's a pretty big change in attribution.

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #5 on: November 01, 2015, 04:26:02 AM »
Zwally ends in 2008, uses ers and icesat. McMillan
http://onlinelibrary.wiley.com/doi/10.1002/2014GL060111/abstract

covers 2010-2013 and uses cryosat, and sees mass loss in all sectors.

AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #6 on: November 01, 2015, 09:57:37 AM »
Interesting. Where's the now "stranded" 0.5mm/yr coming from then? Greenland and mountain glaciers? That's a pretty big change in attribution.

As this period roughly coincides with the faux hiatus, don't forget unexpectedly high increases in ocean heat content and/or above average losses in land storage of water (say due to droughts).
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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #7 on: November 01, 2015, 12:20:13 PM »
I don't 'get' the other stuff however.
????

Sorry about that. I'll explain.

To downplay what's going on in the Arctic, climate risk denier websites (especially WUWT) abuse and distort a quote by Jay Zwally to suggest he said that the Arctic would be ice-free by 2012. But he said 'could', of course, and the part of his quote they won't show is that he said 'at this rate (up to and including 2007)'.

Anyway, now suddenly Zwally isn't an alarmist anymore on those climate risk denier sites because they like the result of this research, but they will trot out the lie next year again when the Arctic doesn't go ice-free. I was referring to this hypocrisy.
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AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #8 on: November 02, 2015, 04:46:26 PM »
The linked Christian Science Monitor article, indicates that Zwally believes that Antarctic ice mass loss is accelerating faster than any trend for ice mass gain:

http://www.csmonitor.com/Science/2015/1101/Antarctica-is-actually-gaining-ice-says-NASA.-Is-global-warming-over

Extract: "Climate scientists caution that these findings don’t mean it’s time to start celebrating the end of global warming. More than anything, the paper shows how difficult it is to measure ice height in Antarctica and that better tools are needed.
It could take only a few decades for the ice melt in Antarctica to outweigh the ice gains, the paper's authors say.
“I don’t think there will be enough snowfall increase to offset these losses,” Jay Zwally, NASA glaciologist and lead author of the study, said in a press release."
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A-Team

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #9 on: November 02, 2015, 05:33:58 PM »
This is so bizarre to see this article get a second wind after its massive coverage back on October 2nd. Despite it being open access (http://tinyurl.com/naynesm), it seems that no one has even glanced at it. It was not published in a 'discussion journal' so reviewer comments are not available.

The subject of the article covers so much ground and has such a long history, I would want to see responses from other experts in this area, especially on the error bars and obsolete instrumentation. Why, in 2015, are we looking at a data cutoff of 2008? It seems this could have been published in 2009.

http://www.nature.com/news/gains-in-antarctic-ice-might-offset-losses-1.18486
http://www.sciencedaily.com/releases/2015/10/151030220523.htm
http://www.nasa.gov/feature/goddard/nasa-study-mass-gains-of-antarctic-ice-sheet-greater-than-losses
http://www.tandfonline.com/doi/abs/10.1080/01490419.2014.969458 (difficulties converting Antarctic mass loss to sea level equivalent)

Quote
So much ice is piling up in the vast expanses of East Antarctica that, overall, it counterbalances the losses seen at glaciers thinning elsewhere on the frozen continent. It will take decades for Antarctic melting to overtake the mass gains and begin contributing substantially to sea-level rise, a new study argues.

The calculations are the latest in a long-running effort to weigh Antarctica’s ice. Whereas melting in Greenland has dramatically reduced its ice sheet, the situation in Antarctica is more complex.

“Parts of Antarctica are losing mass faster than before,” says Jay Zwally, a glaciologist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and lead author of a paper to appear in the Journal of Glaciology1. “But large parts have been gaining mass, and they’ve been doing that for a very long time.”

The findings do not mean that Antarctica is not in trouble, Zwally notes. “I know some of the climate deniers will jump on this, and say this means we don’t have to worry as much as some people have been making out,” he says. “It should not take away from the concern about climate warming.” As global temperatures rise, Antarctica is expected to contribute more to sea-level rise, though when exactly that effect will kick in, and to what extent, remains unclear.

But the work does highlight lingering uncertainties about Antarctica’s ice sheets, says Edward Hanna, a climatologist at the University of Sheffield, UK, and leader of a 2013 review that explored the difficulties in measuring ice sheets.

Many earlier studies have found an overall net loss of ice from Antarctica. A 2012 review, which aimed to reconcile findings from the many techniques that are used to measure ice-mass balance, calculated a loss of 72 billion tonnes of ice from the entire Antarctic ice sheet each year between 2003 and 2008. For roughly the same period, Zwally’s team calculated a gain of 82 billion tonnes a year.

Zwally and his colleagues used data on the changing height of the ice-sheet surface from the European Space Agency’s European Remote Sensing radar satellite between 1992 and 2001, and from NASA’s ICESat laser-ranging satellite between 2003 and 2008.

Across the period of the study, East Antarctica gained the most mass, followed by the West Antarctic interior. Glacial ice forms as snow compresses under its own weight. In this case, the gain in ice mass in parts of Antarctica has not come from snowfall in the modern era, but from heavier snows that fell about 10,000 years ago, says Zwally. That snow became ice and started to flow slowly towards the sea — but so slowly that the ice began to thicken.

The effect is not big — a little more than a centimetre of thickening each year. But over thousands of years, and over the vast expanse that is East Antarctica, those tiny bits of extra ice add up to a lot of extra mass.

Disputes about the rate of Antarctic ice loss will probably continue. The gravity-measuring Gravity Recovery and Climate Experiment (GRACE) satellites, run by NASA, have measured accelerating losses in Antarctica (although Zwally argues that the discrepancy is due at least partly to how GRACE researchers account for changes in the height of the bedrock as ice melts). And ESA’s Cryosat-2 radar satellite found small losses5 in that region in 2010–13.

More work is needed to understand the various measurements obtained using different techniques over different time periods, says polar scientist Andrew Shepherd of the University of Leeds, who led the 2012 reconciliation effort.

Mass gains of the Antarctic ice sheet exceed losses.
HJ Zwally, H. Jay, J Li JW Robbins, JL Saba, D Yi, AC Brenner
Journal of Glaciology, 2015 DOI: 10.3189/2015JoG15J071
« Last Edit: November 02, 2015, 05:40:50 PM by A-Team »

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #10 on: November 02, 2015, 06:07:04 PM »
doi: 10.1126/science.1228102  Shepherd(2012) looks at various different estimates, and reconciles them.

Cryosat has best to date coverage of the fast flow regions where dynamic thinning is largest, see fig 2. in McMillan(2014) and covers 2010-2013  doi: 10.1002/2014GL060111

Comes up with mass waste in all regions of AIS, concludes

"We estimate that, since 2010, the average Antarctic ice sheet contribution to global sea level
rise has been 0.45 ± 0.14 mm yr-1. This value, which is more than twice as large as the 20-
year mean determined from an ensemble of geodetic techniques (0.19 ± 0.15 mm yr-1 in
Shepherd et al., 2012), ..."

sidd
« Last Edit: November 02, 2015, 06:24:10 PM by sidd »

wili

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #11 on: November 02, 2015, 06:34:46 PM »
Here's the coverage from the IBTimes: http://www.ibtimes.com/global-warming-2015-antarctica-actually-gaining-ice-it-wont-last-2164285

Global Warming 2015: Antarctica Actually Gaining Ice, But It Won't Last

Quote
“If the losses of the Antarctic Peninsula and parts of West Antarctica continue to increase at the same rate they’ve been increasing for the last two decades, the losses will catch up with the long-term gain in East Antarctica in 20 or 30 years -- I don’t think there will be enough snowfall increase to offset these losses,” Zwally acknowledged.
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AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #12 on: November 02, 2015, 06:39:36 PM »
This is so bizarre to see this article get a second wind after its massive coverage back on October 2nd.

Quote
Zwally and his colleagues used data on the changing height of the ice-sheet surface from the European Space Agency’s European Remote Sensing radar satellite between 1992 and 2001, and from NASA’s ICESat laser-ranging satellite between 2003 and 2008.

Across the period of the study, East Antarctica gained the most mass, followed by the West Antarctic interior. Glacial ice forms as snow compresses under its own weight. In this case, the gain in ice mass in parts of Antarctica has not come from snowfall in the modern era, but from heavier snows that fell about 10,000 years ago, says Zwally. That snow became ice and started to flow slowly towards the sea — but so slowly that the ice began to thicken.

The effect is not big — a little more than a centimetre of thickening each year. But over thousands of years, and over the vast expanse that is East Antarctica, those tiny bits of extra ice add up to a lot of extra mass.

Disputes about the rate of Antarctic ice loss will probably continue. The gravity-measuring Gravity Recovery and Climate Experiment (GRACE) satellites, run by NASA, have measured accelerating losses in Antarctica (although Zwally argues that the discrepancy is due at least partly to how GRACE researchers account for changes in the height of the bedrock as ice melts). And ESA’s Cryosat-2 radar satellite found small losses5 in that region in 2010–13.

More work is needed to understand the various measurements obtained using different techniques over different time periods, says polar scientist Andrew Shepherd of the University of Leeds, who led the 2012 reconciliation effort.

Mass gains of the Antarctic ice sheet exceed losses.
HJ Zwally, H. Jay, J Li JW Robbins, JL Saba, D Yi, AC Brenner
Journal of Glaciology, 2015 DOI: 10.3189/2015JoG15J071

First, it is evident that this article is experiencing a second life because the denialosphere is promoting it in the media.

Second, as Zwally et al (2015) focus on both radar and laser measurements, and as most other sources of SLR contribution have been well studied; I believe that we should not discount the probability that Zwally et al. (2015) are not appropriately accounting for bedrock recovery due to ice mass loss in the WAIS.  If so, then the true ice mass loss from the WAIS may actually be higher than previously/currently expected (too bad that the US Congressional House Science and NASA Committees are controlled by denialists who are actively starving the budgets needed to gather the data necessary to reduce such doubts).
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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #13 on: November 02, 2015, 09:20:39 PM »
Quote
this article is experiencing a second life because the denialosphere is promoting it in the media.
The beauty of that is it flushes out the media players willing to play along. A lot of them are not making it on online ads, almost everything you read today is a 'paid placement', what they call 'native advertising' and what I call 'fraudulent practice'. And you will find plenty of it from the NYTimes on down.

It's very rare to see the press put out anything on climate that doesn't include 'balancing quotes' to create the impression of controversy and undercut any warning. Here they had a full month and no shortage of scientists who had studied the same topic to different effect.

Data to 2008, Zwally in attendance at the 2012 Reconciliation Conference, scientists being more argumentative than lawyers, this being 2015. Come on.

It wouldn't be too hard to find a quote to the effect: (1) 'well Greenland, thermal expansion etc are certainly not contributing that huge extra to SLR and (2) SLR is measured independently and errors were beaten into the ground long ago, ergo (3) 'Zwally should have gone back to locate the source of his error and fix before publishing'. Saying an unresolved discrepancy like this is 'beyond the scope of the current paper' just doesn't cut it.

I finally located a diplomatic comment from a scientist very experienced in these kinds of measurements:

"The new study highlights the difficulties of measuring the small changes in ice height happening in East Antarctica," said Ben Smith, a glaciologist with the University of Washington in Seattle who was not involved in Zwally's study.

"Doing altimetry accurately for very large areas is extraordinarily difficult, and there are measurements of snow accumulation that need to be done independently to understand what's happening in these places," Smith said.

http://www.sciencedaily.com/releases/2015/10/151030220523.htm

AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #14 on: November 03, 2015, 05:44:12 AM »
The linked Aljazeera article discusses how controversial this paper is, and how many experts (& I believe that Eric Rignot is a true Antarctic Ice Sheet expert) are questioning the conclusions:

http://america.aljazeera.com/articles/2015/11/2/experts-dispute-nasa-antarctic-ice-gain-study.html

Extract: "“There is no quality data to support the claims made by the authors of [ice] growth in East Antarctica,” said Eric Rignot, principle scientist for the Radar Science and Engineering Section at NASA’s Jet Propulsion Laboratory.

But the lead author of the contested report, Jay Zwally, a glaciologist at NASA’s Goddard Institute for Space Studies, told Al Jazeera his data are based on improved models that weren’t applied to previous measurements. If the same model were applied to other data, it would match his own “more accurate” determination of the state of Antarctica’s ice sheets, Zwally said."
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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #15 on: November 03, 2015, 11:32:11 AM »
Quote
Zwally told Al Jazeera his data are based on improved models that weren’t applied to previous measurements. If the same model were applied to other data, it would match his own “more accurate” determination of the state of Antarctica’s ice sheet.

How does Zwally know his models are 'improved' not just relative to previous models but to physical reality?

Without yet having applied his model to the other data, how does Zwally know it would match his own 'more accurate' determination?

So Zwally is saying there is no need for further studies -- that mentioned below by Ben Smith is a waste of taxpayer money because we are already sure?

The guy seems utterly oblivious to the impact he is having, with strong claims getting ahead of anything with reliable experimental support or community consensus. The question is, suppose the conclusion is later refuted -- how is the confusion and damage undone?

Considered just as an internal debate within an academic specialty, Zwally is making a bold claim for glory by challenging the existing paradigm. If it works out, he becomes an academic star; if it doesn't work out, his research has basked in a whole lot of attention (whereas the mistake part will be disputed for years and eventually lost in a muddle). A win-win situation -- if the broader picture of climate consequences is set aside.

Quote
“Please don’t publicize this study,” said Theodore A. Scambos, a senior research scientist at the National Snow & Ice Data Center, a polar research center at the University of Colorado at Boulder.

Other critics said the study contradicts 13 years of satellite measurements of Antarctica’s ice by NASA’s GRACE mission.

“There is no quality data to support the claims made by the authors of [ice] growth in East Antarctica,” said Eric Rignot, principle scientist for the Radar Science and Engineering Section at NASA’s Jet Propulsion Laboratory.

But the lead author of the contested report, Jay Zwally, a glaciologist at NASA’s Goddard Institute for Space Studies, told Al Jazeera his data are based on improved models that weren’t applied to previous measurements. If the same model were applied to other data, it would match his own “more accurate” determination of the state of Antarctica’s ice sheets, Zwally said.

Zwally’s model focuses on the movement of the bedrock deep under Antarctica’s ice. Earth’s mantle rises when relieved of the burden of ice sheets and glaciers. The same phenomenon occurred in Antarctica, Zwally said, but it hasn’t been accurately included in the old models of bedrock movement. That, he said, may be behind the difference between his measurements and those of the rest of the scientific community.

The old models “didn’t take into account the slow growth (in ice) at the center. So we estimated that that unaccounted-for growth is about a centimeter (0.39 inch) or two a year over 10,000 years. That’s … meters on top of the other ice. And instead of the Earth coming up because the ice went away, it’s going down because of that,” Zwally said.

Benjamin Smith, of the University of Washington’s applied physics lab, said he didn’t think there was inaccurate data in Zwally's study. The differences in conclusion with other studies, he said, were largely based on the interpretation of that data. It was possible, Smith said, that Zwally’s measurements were correct and previous data were wrong.

“There’s an interpretation step that needs to go into this. The GRACE measurements and his are both influenced by what rock is doing underneath the ice sheet,” Smith said. “You have to understand what’s happening with the rock motion to understand what the signal from GRACE means.”

Smith said the issue may be laid to rest soon. There are plans underway, he said, to send teams to Antarctica to take measurements of the ice's altitude that way rather than using satellite data.
« Last Edit: November 03, 2015, 11:52:05 AM by A-Team »

nukefix

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #16 on: November 04, 2015, 11:10:14 AM »
I think the other disputed part is Zwally's firn-correction model and the associated error-bars. Ask him how he estimated those errors.
« Last Edit: November 04, 2015, 11:26:38 AM by nukefix »

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #17 on: November 04, 2015, 06:24:01 PM »
The linked Carbon Brief discussion on this topic offers useful insight:

http://www.carbonbrief.org/qa-is-antarctica-gaining-or-losing-ice

Extract: "Measuring ice changes on Antarctica has long been problematic – particularly on East Antarctica. The many different satellite missions of different durations makes it tricky to get a consistent view of what is happening to the ice sheet.

The findings of the new NASA study are “at least somewhat at odds with multiple lines of other evidence,” says Prof Richard Alley from Penn State University, who wasn’t involved in the research. He points to another recent paper – which some of the authors of the new study also contributed to – as the current scientific consensus on ice loss from Antarctica. That paper found changes between 1992 and 2011 of +14bn, -65bn and -20bn tonnes of ice per year on East Antarctica, West Antarctica, and the Antarctic Peninsula, respectively.

Prof Andy Shepherd from the University of Leeds, who led the study that Alley refers to, says the NASA study attempts the difficult job of accounting for snowfall, which can mask changes in ice sheet thickness. He tells Carbon Brief:

"It’s right to attempt this, but in places where nothing much happens – like the interior of Antarctica, which is a vast a desert – it’s really quite difficult to be sure that snowfall can be simulated with enough precision to detect ice imbalance."

Prof Jonathan Bamber, a professor at the University of Bristol whose work focuses on satellite monitoring of the ice sheets, says there are also potential pitfalls in combining radar and laser satellite data for the two different time periods, as the NASA study does. He tells Carbon Brief:

"At a whole ice sheet scale, the results between the two time periods that they study appear to be consistent. But when you start to look at a slightly smaller regional level – and I’m still talking about thousands of kilometres – then it is doesn’t appear to be quite so consistent, and that is a bit of a worry."
 
Nonetheless, Bamber says, the reasons the researchers give for inconsistencies in previous estimates of ice changes on Antarctica and why their estimates are different, are “completely plausible”."

See also:
https://www.skepticalscience.com/is-antarctica-gaining-or-losing-ice.html
« Last Edit: November 04, 2015, 11:46:08 PM by AbruptSLR »
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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #18 on: November 04, 2015, 11:53:55 PM »
"Where's the now "stranded" 0.5mm/yr coming from then? Greenland and mountain glaciers? That's a pretty big change in attribution."

I posted this over in skepticalscience, but it expands on the thought above.
 
Due to the hard work by Cazenave, Leuilette, Miller and many others the sea level budget was thought to be balanced between steric and mass components, with the latter estimated at 1.5mm/yr. Now, if this paper is to be believed, something other than Antarctica is contributing 0.5 mm/yr to mass component of SLR. This leaves Greenland melt, GIC (other glaciers and ice caps) melt, and land aquifer withdrawal as candidates. I find it quite difficult to believe that any of these was underestimated to such an extent.

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #19 on: November 05, 2015, 02:01:09 PM »
The sea-level-budget from various sources has not been successfully closed yet, i.e. the different contributions do not add up. There are efforts addressing this discrepancy but so far no clear solution.

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #20 on: November 05, 2015, 08:29:47 PM »
I thought Fig 4 in Cazenave(2014) DOI: 10.1038/NCLIMATE2159 was quite convincing ...


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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #21 on: November 05, 2015, 11:28:37 PM »
Quote
Zwally said that while other scientists have assumed that the gains in elevation seen in East Antarctica are due to recent increases in snow accumulation, his team used meteorological data beginning in 1979 to show that the snowfall in East Antarctica actually decreased by 11 billion tons per year during both the ERS and ICESat periods. They also used information on snow accumulation for tens of thousands of years, derived by other scientists from ice cores, to conclude that East Antarctica has been thickening for a very long time.

“At the end of the last Ice Age, the air became warmer and carried more moisture across the continent, doubling the amount of snow dropped on the ice sheet,” Zwally said.

The extra snowfall that began 10,000 years ago has been slowly accumulating on the ice sheet and compacting into solid ice over millennia, thickening the ice in East Antarctica and the interior of West Antarctica by an average of 0.7 inches (1.7 centimeters) per year. This small thickening, sustained over thousands of years and spread over the vast expanse of these sectors of Antarctica, corresponds to a very large gain of ice – enough to outweigh the losses from fast-flowing glaciers in other parts of the continent and reduce global sea level rise. 

I don't get it. Zwally says the ice has been thickening thanks to heavy snowfall starting 10,000 years ago, not due to snows in the modern era.
So: does he mean that this old snow is turning into ice and causes it to thicken? If that is the case, then the total mass of water in Antarctica is not growing. Ice is growing at the expense of firn/snow.

If not then what? What's the relevance of snows that fell 10,000 years ago? I must be having serious comprehension problems here.

nukefix

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #22 on: November 06, 2015, 12:57:43 PM »
I thought Fig 4 in Cazenave(2014) DOI: 10.1038/NCLIMATE2159 was quite convincing ...
Those are the de-trended components, I guess the contributions that make up the trend do not fully add up.

nukefix

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #23 on: November 06, 2015, 12:59:47 PM »
If not then what? What's the relevance of snows that fell 10,000 years ago? I must be having serious comprehension problems here.
Ice-history matters since changes in ice-mass cause movements of the earths crust that takes millennia to play out.

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #24 on: November 06, 2015, 11:36:09 PM »
Let me try sharpen the question:

1)Zwally: Antarctica has been gaining 100 Gton/yr between 1993-2008, a total of about 4mm SLR

2)GRACE: Antarctica has lost 2.5 mm equiv SLR over that period

Let's even say GRACE is wrong on Antarctica. But, GRACE cant just be wrong about Antarctica. It has to be wrong about at least one or more of four other things

a)total ocean mass change
b)Greenland melt
c)landwater withdrawal
d)ocean mass change distribution (Riva(2010) doi:10.1029/2010GL044770 is a nice paper)

Can't be done . If one claims that Greenland is melting faster or landwater withdrawal is faster to keep ocean mass increase the same, you run into d) that the fingerprint would different. One needs a vast conspiracy, so that Antarctica is gaining mass, but an exactly equivalent and geographically co-located source is losing mass faster...

So, let's even say,  GRACE is totally wrong about everything, all data from GRACE are lies from Satan.
But that graph from Cazenave above uses ocean mass data from GRACE. They would have to get steric effect and landwater withdrawals wrong by exactly the right amount to come even close to the observations ...

Wow. This conspiracy is bigger than i thought. Gonna need a thicker tinfoil hat.

sidd
« Last Edit: November 06, 2015, 11:48:53 PM by sidd »

Timothy Astin

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #25 on: November 07, 2015, 02:02:19 AM »
Zwally et al. don't reference  Harig and Simons 2015 Accelerated West Antarctic ice mass loss continues to outpace East Antarctic gains. EPSL, 415, 134-141.

Yet it was published just before they submitted their manuscript, and before they revised the paper.
Given how diametrically opposite the conclusions drawn from GRACE data are to the Zwally et al. conclusions, it was surely necessary to draw the readers' attention to the difference between observational methods in the discussion.

As highlighted up thread, the GRACE data are analysed over a longer time window, and are consistent with a wide range of observational data. Clearly Zwally et al. overplay their hand in their conclusions and their abstract.

 

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #26 on: November 07, 2015, 04:00:32 AM »
1)I was wrong in that fig 4 from Cazenave(2014) does not directly use GRACE data, but a comparison is done in the supplementaries and the results agree

2)To believe both Cazenave(2014) and Zwally(2015) you have to simultaneously believe that

a)GRACE ice mass waste distribution is wrong
b)GRACE SLR fingerprint is wrong

and that

c)GRACE landwater withdrawal is correct
d)GRACE ocean mass change is correct
e)temporal variation to interannual scale of c) and d) is correct

I dont think you can satisfy all these at once, especially the temporal signal in e)

sidd
« Last Edit: November 07, 2015, 04:15:38 AM by sidd »

oren

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #27 on: November 07, 2015, 05:04:52 AM »
I again raise my layman's question: could Zwally mean that Antarctic ice has gained mass at the expense of Antarctic snow and firn? And intentionally states it in a confusing way?

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #28 on: November 07, 2015, 05:20:40 AM »
Zwally is quite clear: Antarctica gained mass from 1993-2008

"Ice, Cloud and land Elevation Satellite (ICESat) data (2003–08) show mass gains from snow accumulation exceeded discharge losses by 82 +/- 25 Gt/yr, reducing global sea-level rise by 0.23 mm/yr. European Remote-sensing Satellite (ERS) data (1992–2001) give a similar gain of 112 +/- 61 Gt/yr. "

plinius

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #29 on: November 07, 2015, 04:56:53 PM »
I think one question that needs quantification here is: how much can GRACE be systematically biased by crustal mass change. Long-term snow accumulation would push the continent down, and in my naive view would give a negative mass balance bias. So, if that one is wrongly estimated, it might push the GRACE estimates up a little bit.

Still agree - the conclusions about sea level rise would be very unsettling, if actually east antarctica would contribute with opposite sign.

steve s

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #30 on: November 07, 2015, 09:05:07 PM »
What would the impact on the estimates be if Zwally failed to properly factor in the effect of the past rise in mean sea level on the change in the mass of ice above sea level? The mass decrease implied, correcting for the mass grounded on rock above sea level, seems roughly similar to the increase Zwally claimed. 

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #31 on: November 07, 2015, 09:58:38 PM »
Zwally is an old campaigner, sea level was concurrently measured.

"We apply ICESat laser campaign bias corrections derived from laser measurements of the sea surface height (SSH) over open water and thin ice in leads and polynyas within the Antarctic and Arctic sea-ice packs, with adjustments for SSH variations measured by Envisat radar altimetry concurrently with ICESat measurements (see Appendix)"

The Appendix has chapter an verse.

Timothy Astin

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #32 on: November 07, 2015, 11:29:55 PM »
Plinius' asks a good question.  Harig and Simons did incorporate isostatic adjustment via two different models

https://www.princeton.edu/geosciences/people/simons/pdf/EPSL-2015a.pdf

"We corrected for the ongoing solid Earth deformation from prior changes in ice load by subtracting a glacio-isostatic adjustment (GIA) model projected onto the same basis. We report results using two recent GIA models, both also used by Shepherd et al. (2012): the IJ05_R2 (Ivins et al., 2013) model (in the Main Text) and the W12a_v1 model (Whitehouse et al., 2012 )in the Supplementary Material."

There could be bias in these models.  But at first glance, the same biases would be in the isostatic model adjustments that Zwally et al. made also.

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #33 on: November 08, 2015, 05:07:17 AM »
Zwally:

"from the model we use (Ivins and others, 2013), another
recent model (Whitehouse and others, 2012) and our
previous (Zwally and others, 2005) average of three models
(Ivins and others, 2001; Huybrechts, 2002; Peltier, 2004) are
compared in Table 8."

I think one key difference is the ice load/unload history they use:

"The ice-loading histories typically treated in the models are episodic ice unloadings during a glacial–interglacial transition, which cause relatively rapid isostatic adjustments, followed by a much slower residual response rate decaying over thousands of years. In contrast, our finding of a stable dynamic thickening of 1.59 cm/yr over EA (Table 2), along with our interpretation as long-term dynamic thickening for 10 ka since the early Holocene, implies a slow long-term ice loading resulting in the addition of 159 m of ice averaged over EA in 10 ka."


AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #34 on: November 08, 2015, 08:46:55 PM »
For what it is worth, I note that the topic of the influence of ice mass loss/gain on tectonic response in Antarctica is a complex, and rather confusing, topic that may take a decade or more to clarify as discussed extensively in the "Antarctic Tectonics" thread at the following link:

http://forum.arctic-sea-ice.net/index.php/topic,393.msg27128.html#msg27128

With such high uncertainty as how to correctly model Antarctic isostatic rebound, it seems to me that Zwally et al (2015) may be premature in claiming that they are right and other researchers are less right.
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AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #35 on: November 10, 2015, 04:05:29 PM »
Per the linked article, Prof Andrew Shepherd of the University of Leeds says that Zwally et al. (2015) only has a 5 to 10% chance of providing a correct projection:

http://www.theguardian.com/environment/2015/nov/09/worlds-climate-about-to-enter-uncharted-territory-as-it-passes-1c-of-warming

Extract: "Prof Andrew Shepherd, at the University of Leeds, said a recent Nasa study indicating that ice mass grew in Antarctica from 2003-2008 was contradicted by 57 other studies and had just a 5-10% chance of being a correct prediction."
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A-Team

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #36 on: November 11, 2015, 01:52:40 AM »
Zwally is never ever going to live this down, so tone deaf to go on an egotistical rant on the very eve of the Paris conference. I hope every single one of his gratuitous braggadocio quotes is being saved to throw back at him for the rest of his career.

The paper was fine, the arrogant attacks on all and sundry were not. Some good will come out of this however as it will cause the whole matter to be thoroughly revisited and the issue put to rest.

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #37 on: November 11, 2015, 05:55:20 PM »
Are the data used to generate the Zwally et al. figures available anywhere?  I've tried to make sense of Figures 3, 6, 9, 10, and 11 but the wacky colormaps make it nearly impossible to see what's going on.  I'd love to re-plot them in a sensible diverging colormap, excepting 3b which warrants a monotonic colormap. 

johnm33

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #38 on: November 11, 2015, 08:35:00 PM »
Are the data used to generate the Zwally et al. figures available anywhere?  I've tried to make sense of Figures 3, 6, 9, 10, and 11 but the wacky colormaps make it nearly impossible to see what's going on.  I'd love to re-plot them in a sensible diverging colormap, excepting 3b which warrants a monotonic colormap. 
Open access here http://www.ingentaconnect.com/content/igsoc/jog/pre-prints/content-ings_jog_15j071 interesting critique here http://www.realclimate.org/index.php/archives/2015/11/so-what-is-really-happening-in-antarctica/
john

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #39 on: November 11, 2015, 10:11:35 PM »
Quote
Are the data used to generate the Zwally et al. figures available anywhere? ried to make sense of Figures 3, 6, 9, 10, and 11 but the wacky colormaps
I can all but guarantee that the underlying data is not available. Certainly not at the journal link above, not in supplemental, and not in any article links purporting to be to the data.

In fairness to Zwally, this is custom-and-culture in glaciology: 3rd rate graphics in stupid color schemes from which the data used to generate the graphic cannot be extracted. You can spend all day chasing dead links to data supposedly at NSIDC or supposedly available in cited earlier articles.

Yesterday I even found a Jakobshavn article pdf from which only all-black graphics could be extracted! The authors had supplied an unlabeled fourier transform from which the pdf images could apparently be generated from someone in the know. So you're reduced to screenshots in cases like this.

The reason this mickey mouse is not allowed in other areas of science is that i makes the paper non-reproducible by third parties. Of course authors don't want anybody looking too closely at the data (even though it is in the public domain the minute it is published). And the reviewers pass on it because they too write articles and don't want anybody else analyzing the primary data.

The same thing went on in molecular biology until NIH cracked the grant whip (in the late 1990's) and required everything to have a GenBank accession number at the time of publication. A few researchers are still fighting this 20 years later but the journals aren't buying it. Today you can get a permanent doi for just about anything allowing your data to be located in the future. Storage online? Pennies per year.

Nearly everything now is presented first at a meeting in the form of powerpoints. So authors make some 'presentation quality' eye candy, flash it for 30 seconds across a screen, and then months later re-purpose it as a figure in a journal submission.

Some people see medical and climate research as critically collaborative endeavors. Others see them as purely competitive: you don't advance your career by sharing data with others, on the contrary it's better to stonewall them. As was done here by Zwally.

The other half of the equation is not evil intent but just widespread graphics illiteracy, especially on legend color keys. It's not like anyone ever took a course in scientific illustration. Instead a menu command in a fancy non-scientific software bought off the grant spews out an inappropriately colored graphic that is semi-pleasing in appearance and good enough for the journal, end of interest.
« Last Edit: November 11, 2015, 10:25:39 PM by A-Team »

AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #40 on: November 12, 2015, 12:42:36 AM »
The linked RealClimate article by Jonathan Bamber, University of Bristol, discusses the implications of Zwally et al. (2015):

http://www.realclimate.org/index.php/archives/2015/11/so-what-is-really-happening-in-antarctica/

Extract: "So what is really happening? One thing that Zwally’s study does highlight is how difficult it is to nail what is happening in East Antarctica because the signal is small and contaminated by unwanted effects that are as large or even larger. Zwally et al get a different result from previous studies because they make a different set of assumptions. Those assumptions are, by their nature, subjective and difficult, without additional evidence, to corroborate. There are, however, other lines of evidence that suggest that Antarctica is unlikely to have been gaining mass in the last few decades. That would, for example, make closing the sea level budget a whole lot harder (that is, making the sum of the sinks and sources match the observed rate of sea level rise)."
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James Lovejoy

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #41 on: November 13, 2015, 10:07:25 PM »
Csnavywx  November 01, 2015, 02:52:39 AM
Quote
"Where's the now "stranded" 0.5mm/yr coming from then? Greenland and mountain glaciers? That's a pretty big change in attribution."

An additional question is, according to Zwally, East Antarctica has been gaining about 1.6cm of ice a year for 10,000 years.  By my crude calculations, that would amount to a drop of sea level of about 4 meters.  The evidence is that sea level has been steady to increasing for the last several thousand years.  So how does one account for the difference?  One way is to assume that the ocean has heated up enough for thermal expansion to offset the water loss.  By my calculations that would require 7 to 10 C degree of the entire ocean.  I'm not buying it.  Any other ideas?

AbruptSLR

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #42 on: November 14, 2015, 12:23:17 AM »
I'm not buying it.  Any other ideas?

The most honest idea that comes to mind is that Zwally et al. (2015) is wrong, unless during the past 10,000 year period when they say that the EAIS was gaining mass, some combining of the GIS & the WAIS were losing mass at nearly the same rate.
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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #43 on: November 16, 2015, 05:54:27 PM »
For what it is worth (a lot!), here is a series of 4 animations about the GRACE data. (I'll not re-post them as the files are large, NASA pages are stable, and I'm not 'adding value' to them at this point.)

Quote
Antarctic Mass Change from GRACE derived Gravity Observations: Jan 2004 - Jun 2014
Visualizations by Cindy Starr on October 27, 2015

GRACE, NASA's Gravity Recovery and Climate Experiment, consists of twin co-orbiting satellites that fly in a near polar orbit separated by a distance of 220 km. GRACE precisely measures the distance between the two spacecraft in order to make detailed measurements of the Earth's gravitational field. Since its launch in 2002, GRACE has provided a continuous record of changes in the mass of the Earth's ice sheets.

These animations show the change in the mass of the Antarctic Ice Sheet between January 2004 and June 2014 as measured by the pair of GRACE satellites. The 1-arc-deg NASA GSFC mascon solution data was resampled to a 5130 x 5130 data array using Kriging interpolation. A color scale was applied where blue values indicate an increase in the ice sheet mass while red shades indicate a decrease. In addition, a graph overlay shows the running total of the accumulated mass change in gigatons.

Four separate animations are shown here: one of the full Antarctic Ice Sheet (above) and three of individual regional views (below) showing the regions of West Antarctica, the Antarctic Peninsula and East Antarctica. The time-series of each region is shown with a graph depicting the ice loss for the region alone. Note that the range on the color scale is different for each regional view in order to portray the most detail possible. Areas outside the region being shown are colored in a pale green to indicate that it is not included in the view. The floating ice shelves, shown in a lighter shade of green, are also not included.

The glacial isostatic adjustment signal (Earth mass redistribution in response to historical ice loading) has been removed using the ICE-6G model (Peltier et al. 2015).
http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4376

sidd

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Re: NASA: Antarctic Ice Sheet gaining mass?
« Reply #44 on: March 01, 2016, 05:43:04 AM »
I repost a comment i made over at skepticalscience, and include the table and figure:

That Zwally paper is interesting. Set aside the matter of the total mass change for a moment, and look at the changes between 1992-2001 and 2003-2008, the delta column in Table 5 or by eyeball from Fig 9. Mass waste in PIG, Thwaites and neighbours had doubled in the periods covered in the paper, the you can see the hole burning toward Ross, Ronne and the Transantarctic mountains. Recall that we are now in 2016. So apart from an overall constant, the trends agree. Fig 9 indicates that Totten is another place to watch, and I am glad the Amery doesn't seem to be waking up, at least in this data.

Also, the link to

http://svs.gsfc.nasa.gov/cgi-bin/details.cgi?aid=4376

from A-Team has a nice graf demonstrating GRACE measurement of Antarctic mass loss for the later period in Zwally and continuing.