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Friday, November 6, 2015

More snow won't stop the West Antarctic ice sheet from collapsing

Sou | 2:14 AM Go to the first of 6 comments. Add a comment
Anthony Watts reappears in a frenzy of excitement (archived here and cached here). He's discovered a press release about a new paper by scientists from the British Antarctic Survey Expedition, but didn't take the time to read it or the paper. Because of that, he's made a complete ass of himself as he almost always does whenever he writes something on his blog. (Which is probably why he appears so rarely these days. He can't hack the guffaws from onlookers.)

Anthony's headline is wrong. It reads: "Yet another study shows Antarctica gaining ice mass – snowfall accumulation ‘highest we have seen in the last 300 years’". Then, that blogger who rejects out of hand almost every scientific paper he comes across, bemoans the fact that an article at Media Matters tells how a scientist, Jay Zwally, knew that deniers would twist his recent paper.

It's a very contorted mind that Anthony Watts has. Anthony accepts what he thinks is in the Zwally paper, but denounces the lead author. Or denounces an article about the lead author saying that deniers would twist his findings. Anthony only dared write a few words, probably knowing he'd be picked up for getting things wrong again:
While the wailers over at Media Matters bemoan claims of “distortion” over the recent NASA press release about Antarctica gaining ice mass due to increased snowfall over the last 10,000 years,…
A new NASA study says that an increase in Antarctic snow accumulation that began 10,000 years ago is currently adding enough ice to the continent to outweigh the increased losses from its thinning glaciers.
…this new study jointly announced by the AGU and the BAS says that the gains in the 20th century for the West Antarctic are the “highest we have seen in the last 300 years”.

Media Matters reported all the denialist tripe, and at the top of the article there was this:
The study's lead author astutely predicted that climate science deniers would distort the study, even though it does nothing to contradict the scientific consensus on climate change or the fact that sea levels will continue to rise.



Snow is accumulating on a coast in Antarctica, while ice mass is declining


The second half of Anthony's headline is fine: "snowfall accumulation ‘highest we have seen in the last 300 years'", though only for a limited area between the continent of West Antarctica and the Peninsula. The first part: "Yet another study shows Antarctica gaining ice mass" is misleading. The area where the snow is accumulating is also an area where the glaciers and ice sheets are thinning. On balance, there's a big reduction in ice mass in West Antarctica and the Peninsula.

The researchers found that in West Antarctica, on a coastal strip between the Peninsula and the continent, snow accumulation has increased a lot in recent years. There has been more snow build up in the past three decades than in any other time in the past 300 years.

Anthony put up a chart with arrows pointing to various places that didn't seem to be the sites that were the subject of this research. Below is Figure 1 from the paper, with stars showing where the ice cores came from - click to enlarge it:

Fig 1 | (a) Annual average snow accumulation (thin lines) and running decadal means (thick lines) for Gomez [Thomas et al., 2008], Bryan Coast (red), Ferrigno (blue), and WAIS divide WDC05Q [Banta et al., 2008] (green). Solid horizontal lines indicate the average for each record in the period 1980–2010. (b) Spatial correlation plot of Bryan Coast snow accumulation and precipitation—evaporation from ERA-Interim 1979–2010 [Dee et al., 2011]. Stars indicate ice core locations, and brighter coloring indicates p < 0.05. Source: Thomas15

From the BAS press release:
The new study used ice cores to estimate annual snow accumulation from 1712 to 2010 along the coastal West Antarctic. Until 1899, annual snow accumulation remained steady, averaging 33 and 40 centimeters (13 and 16 inches) water, or melted snow, each year at two locations.
Annual snow accumulation increased in the early 20th century, rising 30 percent between 1900 and 2010 and the researchers found that in the last 30 years of the study, the ice sheet gained nearly 5 meters (16 feet) more water than it did during the first 30 years of the studied time period....
...For the new study, researchers collected two ice cores from Ellsworth Land, the strip of land that connects the Antarctic Peninsula to the rest of the continent. The ice cores contain layer upon layer of ice – the remnants of yearly snowfall. By measuring the thickness of the ice laid down each year, the researchers estimated annual snow accumulation for the past 300 years.
The recent heavy snow accrual appears to be part of a gradual, long-term rise in annual snow accumulation that started in the early 1900s and accelerated in the 1980s, the study found. The study’s authors found that starting in the early 20th century an additional 1.5 centimeters (0.6 inches) of water, or melted snow, was added to the ice sheet each decade. From 2001 to 2010, the amount of water added to the ice sheet each year was 15 centimeters (6 inches) greater than it was before 1900, according to the study’s authors.

In the paper, the authors associate the increase in snowfall to sea level pressure and even to ENSO, concluding:
The close relationship between SLP [sea level pressure] and snow accumulation at these sites make this a unique proxy for past ASL [Amundsen Sea Low] (and onshore wind) conditions. The recent deepening trend of the ASL is predicted to continue through the 21st century in response to greenhouse gas concentration increases [Raphael et al., 2015]. The dramatic increase in snow accumulation in Ellsworth Land provides evidence that this recent deepening in the ASL region is part of a longer trend, observed as early as the 1920s, with acceleration since the 1990s when the coupling between ENSO and SAM [Southern Annular Mode] is strongest. 

More snow doesn't offset the loss of ice


If Anthony had taken a couple of minutes to read the paper (it's open access), he would have found that the region has been losing mass, not gaining it:
The Amundsen Sea sector of the West Antarctic ice sheet has been losing mass in recent decades; however, long records of snow accumulation are needed to place the recent changes in context. 

And if he'd read more about the Zwally paper, he'd have seen that they the authors found that snow accumulation had been declining (in East Antarctica), not increasing. The increase in mass that they reported was said to be from a decline in ice movement, not from an increase in snowfall.


To summarise

First the science:
  • On a coastline between the Antarctic Peninsula and the continent, snow is accumulating
  • In the same region, ice mass is declining a lot
  • Zwally15 found that snow accumulation was declining - that's in East Antarctica, not west, while overall mass was increasing slightly (those results are outliers)
To summarise the misleading gumph from Anthony Watts, who doesn't know if its coming or snowing:
  • Antarctica is gaining mass from snow.
But wait, there's more...


More snow is expected in Antarctica with global warming


Antarctica has always been known as the driest continent on the planet. Australia is second driest. In researching this article, I came across another paper in Nature which was about how an increase in snowfall is expected over Antarctica, because the warmer air will bring more moisture. They were reporting estimates of increased snow accumulation, which will offset sea level rise caused by the melting ice sheets. The authors wrote:
In summary, local- as well as continental-scale changes in Antarctic accumulation rates show a remarkably linear relationship with local or continental average warming, respectively. Sensitivities from all four sources used here (ice-core data, palaeo-simulations, CMIP5 GCM future simulations and RCM future simulations) are positive. Palaeo-simulations as well as high-resolution future projections fall into the multi-GCM range of 6.1% K-1 ±2.6% K-1 derived from 35 CMIP5 models. Additional agreement with the sensitivities derived from the ice-core data provides confidence in  projections of enhanced snowfall over Antarctica in offsetting the ice sheet’s dynamical contribution to future sea-level rise. 


There'll be nothing to stop all of West Antarctica melting and raising sea level by ten feet or so


Despite the expected increase in snow with global warming, parts of Antarctica are losing a lot of ice. In another paper this week in PNAS, scientists from the Potsdam Institute for Climate Impact Research (PIK) reported that based on computer simulations, "a few decades of ocean warming can start an ice loss that continues for centuries or even millennia". From the paper:
In our simulations, at 5-km horizontal resolution, the region disequilibrates after 60 y of currently observed melt rates. Thereafter, the marine ice-sheet instability fully unfolds and is not halted by topographic features. In fact, the ice loss in Amundsen Sea sector shifts the catchment's ice divide toward the Filchner–Ronne and Ross ice shelves, which initiates grounding-line retreat there. Our simulations suggest that if a destabilization of Amundsen Sea sector has indeed been initiated, Antarctica will irrevocably contribute at least 3 m to global sea-level rise during the coming centuries to millennia.

In other words, it might have already started.


From the WUWT comments

The comments were the usual mix of people not taking in anything of what they read.

Ian Bryce seems to think snow falls out of a cloudless sky. Maybe he was confusing snow with cold. However in Antarctica, snow is more likely to be associated with warmth than cold (relatively speaking).
November 5, 2015 at 1:57 am
Svensmark appears to be saying that with less cloud cover, the earth warms, but the Antartic is cooler because of the reflection of the radiation by the snow.
jbenton2013 doesn't understand either, that the warmer it gets in Antarctica, the more likely water will evaporate and fall as snow:
November 5, 2015 at 1:59 am
So more warming means more snow. I’m convinced already.

Felflames  is just as bad, not understanding a word of the press release:
November 5, 2015 at 2:03 am
The hat tip to greenhouse gasses is still there, but they seem to be toning it down a lot.
A cynic might think they have an eye on public opinion and are leaving themselves a way out if the CoCC (Cult of Climate Change) collapses.

Ron has got it better, but does he realise that Western Antarctica is losing mass much faster than it's gaining it?
November 5, 2015 at 2:09 am
So more warming means more snow accumulation which means more ice buildup and less sea level rise.
A classic negative feedback.
Settled science? 
markstoval is a hard-core denier at WUWT, and can't wait to get his silly "thought" on screen:
November 5, 2015 at 2:50 am
I was under the impression that 97 percent of climate ‘scientists’ were Positive that they knew what drives our climate to the certainty that we just have to dismantle the progessmof the ages. But now we see yet another post the says they just don’t know jack.
CO2 don’t do what they think it does.

stormy223 is spot on, but probably doesn't know it:
November 5, 2015 at 2:56 am
The alarmists are already working to spin this.
Thomas attributes the higher annual snow accumulation over the last 30 years in part to an intensification of a regional low pressure system and more storms in the region. The study’s authors said these storms could increase with climate change, possibly leading to further increases in snow accumulation. ”
Stand by, the layman explanation will be:
In a warming world, the rise in temperature increases evaporation. The increase in humidity in the cold polar areas result in more snowfall. The models have predicted this all along. 

What on earth does MCourtney mean? Does he think that storms cause holes in the ozone layer?
November 5, 2015 at 2:59 am
Thomas attributes the higher annual snow accumulation over the last 30 years in part to an intensification of a regional low pressure system and more storms in the region.
This finding is backed up by the snow accumulation.
Which is actually very inconvenient for those who blame CFCs for the hole in the Ozone Layer.

seaice corrects Anthony Watts:
November 5, 2015 at 3:13 am
Chaam Jamal has it right. This is not a mass balance. The study only looks at accumulation, not loss. It is wrong to say it is a study showing Antarctica gaining ice mass. You do not have to read between the lines to see this; they actually say it:
Thus the increased snowfall we report here has not led to thickening of the ice sheet…” 

David has an interesting question, especially if you turn it around the way it should go:
November 5, 2015 at 4:28 am
Out of curiosity does anyone know how Antarctica gaining mass will affect the wobble the earth has as it revolves.
It's not quite the same, but he might be interested in this article by Carl Engelking at Discover: Antarctic Ice Melt is Changing Earth’s Gravity


References and further reading


E. R. Thomas, J. S. Hosking, R. R. Tuckwell, R. A. Warren, and E. C. Ludlow. "Twentieth century increase in snowfall in coastal West Antarctica". Geophys. Res. Lett., 42, doi:10.1002/2015GL065750. (open access)

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

Frieler, Katja, Peter U. Clark, Feng He, Christo Buizert, Ronja Reese, Stefan RM Ligtenberg, Michiel R. van den Broeke, Ricarda Winkelmann, and Anders Levermann. "Consistent evidence of increasing Antarctic accumulation with warming." Nature Climate Change (2015). doi:10.1038/nclimate2574 (pdf here)

Johannes Feldmann, Anders Levermann. "Collapse of the West Antarctic Ice Sheet after local destabilization of the Amundsen Basin." Proceedings of the National Academy of Sciences, 2015; 201512482 DOI: 10.1073/pnas.1512482112

6 comments:

  1. Doesn't Hansen 2015, not peer reviewed, find significant snowfall will eventually transition in this century from the continent to the ocean around it?

    ReplyDelete
  2. *Survey* not *Expedition*. That was so last century (http://www.spri.cam.ac.uk/picturelibrary/catalogue/bae1910-13/).

    ReplyDelete
    Replies
    1. Apologies, William.

      I am much more last century than this one :(

      Delete
  3. I think stormy223 should be hired by scientists as an editor. He actually translates academic goobly-gook into real English.

    @Sou
    Point taken that he may not have realised this. Still let's run some other things by him as see if he can make them comprehensible. http://sciencecareers.sciencemag.org/career_magazine/previous_issues/articles/2012_03_23/caredit.a1200033

    ReplyDelete
  4. Did any of Anthony's commentators read the actual paper?

    Ouch I see I missed a space in my earlier post--my apologies

    ReplyDelete
  5. At sites like WUWT there seems to be a generalized lack of imagination or intuition as to how the collapse of an ice sheet could progress. Maybe because I've studied erosion and land forms it comes a bit easier to me, but I can readily visualize a large ice sheet both warming and (regionally and temporarily) increasing in mass as snowfall increases in a warming Antarctic. Ice sheets would become much more dynamic systems, with snowfall racing to keep up with increased sublimation, surface melt or ablation, and ice flowing faster to the sea along receding margins or ice "rivers" extending inland.

    Intuition does not equal evidence, of course, but it helps to picture physical processes that can then be spotted in the field or interpreted through modeling.

    ReplyDelete

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