Arguments
Is Antarctica losing or gaining ice?
What the science says...
| Select a level... |
Basic
|
Intermediate
| |||
|
Satellites measure Antarctica is gaining sea ice but losing land ice at an accelerating rate which has implications for sea level rise. |
|||||
Climate Myth...
Antarctica is gaining ice
"[Ice] is expanding in much of Antarctica, contrary to the widespread public belief that global warming is melting the continental ice cap." (Greg Roberts, The Australian)
Update Nov. 7 2015
A study published by Jay Zwally and his team on Oct. 30 (Zwally et al. 2015) has suggested that until 2008 there might have been a bigger increase in ice on East Antarctica than there is a decrease in the west, meaning that total Antarctic land ice is increasing. While their results for the Antarctic Peninsula and much of West Antarctica agree with other research, the study disagrees with many other techniques. We will update this discussion once more studies address this issue. Until then here are links to some recently published takes on the study:
A controversial NASA study says Antarctica is gaining ice. Here’s why you should be skeptical - Chris Mooney (Nov. 5)
NASA Scientist Warned Deniers Would Distort His Antarctic Ice Study — That's Exactly What They Did - Media Matters (Nov.4)
More on Antarctic Ice Melt - ClimateCrocks (Nov. 3)
Is Antarctica Gaining or Losing Ice? Hint: Losing. - Phil Plait (Nov. 3)
Q&A: Is Antarctica gaining or losing ice? - Carbon Brief (Nov. 3)
Just Because Antarctica Might Be Gaining Ice Doesn't Mean Climate Change Isn't Happening - Vice (Nov. 2)
Skeptic arguments that Antarctica is gaining ice frequently hinge on an error of omission, namely ignoring the difference between land ice and sea ice.
In glaciology and particularly with respect to Antarctic ice, not all things are created equal. Let us consider the following differences. Antarctic land ice is the ice which has accumulated over thousands of years on the Antarctica landmass itself through snowfall. This land ice therefore is actually stored ocean water that once fell as precipitation. Sea ice in Antarctica is quite different as it is ice which forms in salt water primarily during the winter months. When land ice melts and flows into the oceans global sea levels rise on average; when sea ice melts sea levels do not change measurably.
In Antarctica, sea ice grows quite extensively during winter but nearly completely melts away during the summer (Figure 1). That is where the important difference between Antarctic and Arctic sea ice exists as much of the Arctic's sea ice lasts all the year round. During the winter months it increases and before decreasing during the summer months, but an ice cover does in fact remain in the North which includes quite a bit of ice from previous years (Figure 1). Essentially Arctic sea ice is more important for the earth's energy balance because when it increasingly melts, more sunlight is absorbed by the oceans whereas Antarctic sea ice normally melts each summer leaving the earth's energy balance largely unchanged.
Figure 1: Coverage of sea ice in both the Arctic (Top) and Antarctica (Bottom) for both summer minimums and winter maximums
Source: National Snow and Ice Data Center
One must also be careful how you interpret trends in Antarctic sea ice. Currently this ice is increasing overall and has been for years but is this the smoking gun against climate change? Not quite. Antarctic sea ice is gaining because of many different reasons but the most accepted recent explanations are listed below:
i) Ozone levels over Antarctica have dropped causing stratospheric cooling and increasing winds which lead to more areas of open water that can be frozen (Gillet 2003, Thompson 2002, Turner 2009).
and
ii) The Southern Ocean is freshening because of increased rain and snowfall as well as an increase in meltwater coming from the edges of Antarctica's land ice (Zhang 2007, Bintanga et al. 2013). Together, these change the composition of the different layers in the ocean there causing less mixing between warm and cold layers and thus less melted sea and coastal land ice.
All the sea ice talk aside, it is quite clear that really when it comes to Antarctic ice and sea levels, sea ice is not the most important thing to measure. In Antarctica, the largest and most important ice mass is the land ice of the West Antarctic and East Antarctic ice sheets.
Therefore, how is Antarctic land ice doing?
Figure 2: Estimates of total Antarctic land ice changes and approximate sea level contributions using a combination of different measurement techniques (Shepherd, 2012). Shaded areas represent the estimate uncertainty (1-sigma).
Estimates of recent changes in Antarctic land ice (Figure 2, bottom panel) show an increasing contribution to sea level with time, although not as fast a rate or acceleration as Greenland. Between 1992 and 2011, the Antarctic Ice Sheets overall lost 1350 giga-tonnes (Gt) or 1,350,000,000,000 tonnes into the oceans, at an average rate of 70 Gt per year (Gt/yr). Because a reduction in mass of 360 Gt/year represents an annual global-average sea level rise of 1 mm, these estimates equate to an increase in global-average sea levels by 0.19 mm/yr.
There is variation between regions within Antarctica (Figure 2, top panel), with the West Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet losing ice mass, and with an increasing rate. The East Antarctic Ice Sheet is growing slightly over this period but not enough to offset the other losses. There are of course uncertainties in the estimation methods but independent data from multiple measurement techniques (explained here) all show the same thing, Antarctica is losing land ice as a whole, and these losses are accelerating quickly.
Basic rebuttal written by mattking
Update July 2015:
Here is the relevant lecture-video from Denial101x - Making Sense of Climate Science Denial
Last updated on 8 November 2015 by BaerbelW . View Archives
A multivariate analysis of Antarctic sea ice since 1979.
"Circulation changes, in part due to ozone depletion, are responsible for the increase in Antarctic sea ice," would seem more correct.
Our 'side' of the debate is by far the stronger, supported as it is by the weight of peer-reviewed science, and so there need be no reliance on misinformation, no matter how small a nugget of misinformation it is. Therefore all humility and reticence must be shown on sites like Sks, and things like this that have been overlooked must be corrected. Not doing so risks giving those of an anti-science persuasion an excuse to focus on something other than the science!
Of course, the current incarnation of this page is an excellent description of the state of Antarctic ice, no problems there.
[DB] Accusations of dishonesty snipped.
"Therefore all humility and reticence must be shown on sites like Sks, and things like this that have been overlooked must be corrected."
SkS endeavors to keep its focus on the science, not on rhetoric, ideology or invective. Hue and cry from the "skeptics" on things transparently not based in science amount to little more than tone trolling and are typically ignored.
However, your point is made, taken and noted.
Tone trolling should rightly be ignored, but IMO Bishop Hill did have a point, although they vastly overstated the significance of it. That Sks is coming under fire presumably means you're doing a good job, so keep it up!
It seems to be in conflict with the statements in this post as well as he recent paper by Rignot et al, 2011
Does the Zwally paper hold any merits and should it be incorporated in the post?
The Zwally paper re-assessing the data is later than Rignot, and the science is persuasive (in my view). Although in Zwally the estimates of average mass loss have been revised and reduced over the whole continent, there is even less doubt about increasing loss of land based ice in western Antarctica. The linkage with temperature rise in this area is perhaps obvious.
Thank you for the response.
When you write that there is even less doubt about increasing loss of land based ice in western Antarctica, what do you then base that on? The Zwally paper?
Another question, in Zwally the estimated overall ice loss is 31 Gt/year. Could the cause for this be an decrease in precipation over Antarctica?
[DB] If you think about this you'll be able to answer your own question. Any astronomer in the world can tell you that there's no evidence whatsoever for it. GPS systems would be way off. The tides would be different. Satellites that measure earth changes to sub-millimeter accuracy would also provide evidence against it. There is simply no physical evidence to cause such a shift that would not also be felt the world over.
The crustal displacement/polar wander fancies of Hapgood are just that: flights of imagination.
"Although the Alarmist arguments sometimes include claims about ice volume, such claims are based upon sea ice extent and subjective guesses about what they beleive a model parameterization adjustment should be to produce a desired result. Currently, there are no objectively quantitative ice volume measurements with anthing remotely close to the necessary temporal and spatial coverages. Consequently, Morano and anyone else can only make objective observations about sea ice extent."
Is there any validity to this guys argument?
Thanks
Anyone who would maintain otherwise is simply talking about things about which they know nothing...or simply lying with the intent to mislead.
http://neven1.typepad.com/blog/2011/08/polarstern-reaches-north-pole.html
http://neven1.typepad.com/blog/2011/09/more-on-ice-thickness-from-awi.html
http://imb.crrel.usace.army.mil/
http://amap.no/swipa/
http://www.osi-saf.org/index.php
PIOMAS is a useful tool to incorporate all of these metrics into a validated model using known ocean/atmospheric/ice dynamics to compare past observations to current ones:
and
Essentially, the commenter is saying that PIOMAS scientists are faking each month's data point to make sure that volume is dropping like a rock. If you don't understand how sea ice volume is measured, then ask yourself what is the more likely claim:
A) the dozens of scientists at several scientific organizations are knowingly committing fraud to make it look like sea ice volume is dropping. They come to work every day knowing that they're doing the exact opposite of what they're trained to do, the exact opposite of what they went through 6-10 years of college to do.
B) sea ice volume is dropping, consistent with a warming ocean and atmosphere. Volume drop is also corroborated by evidence from people who live and work around the Arctic circle.
A recent example of direct measurement of central Arctic sea ice volume is described in detail in “Changes in Arctic Sea Ice: Young and thin instead of old and bulky.”
To access this informative article, click here.
Can anyone seriously contemplate circumstances in which areal extent is decreasing, but volume is increasing? That's patently ridiculous.
See the Arctic ice threads.
Antarctic sea ice is expected to eventually start declining, but this seems more likely to be some sort of short-term fluctuation. The 'growth' in Antarctic sea ice has been small enough that the current year amount still drops below the long term average semi-regularly. This contrasts with the situation in the Arctic where skeptics got excited earlier this year about the extent coming CLOSE to the long term average for the first time in years. Make sure to read this: get far cry 3. Thus, the current dip is unusual, but not unprecedented. Looks like the Southern melt season started about two weeks early for some reason.
Agreements?
[DB] The article update date is indicative of the last update/rewrite/iteration of the main article. The date of the "update" below that indicates the date of the specific revision mentioned (correction of the incorrect quote).
Being there were crops and vineyards grown in Greenland between the 9th & 12th more or less how warm would temperatures have to get for that to happen again? What caused the temperatures to rise to that point before?
As for underwater volcanoes, presumably they would be very noticeable, being as how the water temperature would get warmer the deeper you go towards those volcanoes ?
[DB] NSIDC has a FAQ on undersea volcanoes here:
http://nsidc.org/asina/faq.html#volcanoes
The only evidence for crops are a few grains of barley found in a Viking-age midden, but that does not confirm whether they were locally-grown or imported. Local growing of barley is maybe possible in the warmest years of the Greenland MWP, but the most sensible explanation is that the Norse Greenlanders imported it, due to a combination of low temperatures and poor soils. It would be a commodity worth trading for, as the Norse were partial to beer!
There are a few active volcanoes in Antarctica, but not enough volcanism to do much damage to a whole ice sheet (ice sheet big, volcanoes small). Iceland is a good example, where Vatnajokull survives happily despite having several active volcanoes under it, notably Grimsvotn and Bardarbunga.
"A 364-metre-long ice core record has revealed an unusual pattern of rapid warming across the Antarctic Peninsula over the past 100 years.
An Australian National University research expedition produced findings dating back 15,000 years, resulting in the first comprehensive temperature record of the Antarctic Peninsula.
Dr Nerilie Abram said the Antarctic Peninsula is one of the fastest warming places on Earth and the findings will allow researchers to compare recent and past temperatures in the region for the first time."
More here.
http://wattsupwiththat.com/2012/09/10/icesat-data-shows-mass-gains-of-the-antarctic-ice-sheet-exceed-losses/#more-70757
The NASA page on it is here.
Watt's the big deal?
Ha ha ha, but more seriously, how long would you expect the mass gain to last, if indeed it is happening?
It also keep in mind that they conclude that:
"A slow increase in snowfall with climate wanning, consistent with model predictions, may be offsetting increased dynamic losses."
If true, one has to wonder for how much longer that might hold?
This abstract was done in July. The point for Watts is provide some reassurance to readers wondering about the arctic meltdown. All his readership cares about is having an excuse to do nothing. I suspect for the average US citizen, the effects of climate change are so far small, in the future, and happening elsewhere, whereas any sort of mitigation is perceived as less spending power by one means or another.
The "big deal", to my mind, is that if the ICESat analysis is robust, there are implications for sea level projections, which of late have been much higher than AR4. I need to go back and read some of those papers, but IIRC the recent hike in sea level projections is strongly rooted in the perceived loss (acceleration?) of Antarctic ice sheet mass balance. AR4 projected a negative sea level contribution from the Antarctic ice sheet.
I don't think SkS should wave these results away, but present them as an update with the appropriate caveats. If Zwally was up for it, a post by him here would be terrific for all sorts of reasons.
Any GCM model-based estimate of sealevel rise would be based on Antarctica accumulating ice. As far as I know, these have only very primitive icesheet dynamics (if any) so sea level results from such an approach are so uncertain that the AR4 statement excluded them entirely. Vermeer and Rahmsdorf instead a semi-empirical approach. This also doesnt incorporate any icesheet dynamics so I dont think this result has any bearing on the estimate at all.
Velicogna 2009 [PDF] discerns comparable mass loss for Greenland and Antarcica, with comparable contributions for sea level rise.
Chen et al 2009 [PDF] conclude with a mass loss for the whole of Antarcica of 190 +/-77 Gt/yr, comparable to higher Greenland mass loss estimates of ~220 Gt/yr. Chen posits that "Using a simple linear projection for the period 2006 - 2009, Antarctic ice loss rate can be as large as -220 +/-89 Gt yr." Sea level contribution is, again, comparable to Greenland.
Inferences on sea level rise from Antarctic mass loss mentioned here (upper bound 1.4 meters by 2100 from Antarctic ice loss). I'll have a better look for papers specifically about sea level/Antarctic ice loss.
A quick search of SkS articles on Antarctic ice mass balance yields a range of estimates from -26Gt/yr to -300 Gt/yr, and acknowledgement that new data showing Antarctic ice loss (as wel as Greenland etc) contributes to higher sea level projections.
The main SkS article on Antarctic ice mass balance (and mentioning sea level) is probably this one. Watts cites it in his article, and for once I find myself agreeing with him (on SkS updating), particularly in light of the final comment on that page.
"Those responses seem a bit cynical."
I hope that you did not interpret my response that way. I'm just advocating caution, especially given the potential significance of this result. This is probably the first step towards Zwally et al. submitting a paper for publication and things can, and do, sometimes change a lot in the intervening steps. These types of data are incredibly finicky and all sorts of corrections need to be made especially for a long-term space-based monitoring platform.
It would be nice to have Dr. Zwally post here, maybe once he has had his paper accepted for publication? If these preliminary findings hold true, this would be the first good news on the global warming front in quite some time.
Anyway, I was scoping google scholar for recent assessments, and found one I'd read a few months ago that probably informed my comments here (as well as remembered SkS posts).
Rignot, Velicogna et al 2011 [PDF]
1. Antarctic ice-mass balance 2002 to 2011:
regional re-analysis of GRACE satellite
gravimetry measurements with improved
estimate of glacial-isostatic adjustment -Sasgen (2012).
2. Variability of mass changes at basin scale
for Greenland and Antarctica - Barletta (2012).
And a forthcoming paper using satellite altimetry from (now defunct?) ENVISAT:
Dynamic thinning of Antarctic glaciers from along-track repeat radar altimetry - Flament & Rémy (2012).
The first two find mass losses are smaller than previous publications suggested, and Barletta (2012) finds a near-neutral mass balance trend in Antarctica between 2002-2007. It has since undergone rapid ice loss since then.
Envisat went offline in April. Lasted 10 years, twice as long as its planned operational life. Various groups are still reprocessing the data.
http://tamino.wordpress.com/2012/09/20/poles-apart/
Warming Oceans Will Start Massive Changes In Antarctic Ice Sheet , by Nathan, PlanetSave, Sep 20, 2012
It will be interesting to see how the results of this new research is spun in Deniersville.
Golledge et al 2012 actually looks to be a very interesting paper - considering how fast moving peripheral glaciers in Antarctica may respond to warming oceans, with the potential to drawdown ice over very large areas. Essentially, at how speeding up these fast glaciers may "unplug" the ice stores over significant portions of Antarctica, allowing it to drain into the oceans.
Proving once again that Watts hs spent wat too much tiome rattling around in the Climate Denial Spin Machine. He can no longer distinguish between up and down, right and left, forward and backward, etc. What is even sadder is that his minions automtically lap up every pile of poppycock that he deposits.
Does the expanding Antarctic sea ice disprove global warming? by Eric Berger, SciGuy Blog, Houston Chronicle, Sep 21, 2012
Berger’s opening sentence: “Ice is a hot topic in the climate science community right now so let’s talk about it.”
Berger’s concluding statement: “The bottom line is that scientists generally have predicted that the Antarctic sea ice will not begin substantially melting until the second half of this century.”
Berger’s blog post was created in response to the recent pious pontifications about polar ice by non-scientists James Taylor and Steve Goddard.
I am a GP (and I am). A patient, a climate change contrarian, shows up in my surgery. He has a painful left leg. After some necessary investigations, he returns for the results.
"I have some bad news", I say, "your investigations show a nasty malignant sarcoma of your left tibia. You will need an amputation to save your life"
"Nonsense" says the contrarian, "I don't believe you, there's nothing wrong with me, look, my right leg is fine, in fact it's better than it's ever been" as he jumps up and down on his one good leg to demonstrate the unimpeachability of his logic.
The issue is that both the Arctic and the Antarctic belong to the same natural entity, indeed if you subscribe to James Lovelock's thesis, the same organism. A healthy planet depends on the healthy functioning of all its parts. That the Antarctic ocean has so far escaped obvious global warming effects (though the Antarctic Peninsula is warming quickly) then this is neither suprising, nor does it prove anything else.
You're quite correct, Antarctic sea ice increase is barely significant, while Arctic ice decrease is extremely significant to the point of being appalling (something the 'skeptics' appear to be hiding from, sticking fingers in ears and singing "lalalala!").
Interestingly enough, this effect of some increase in Antarctic ice is consistent with warming due to anthropogenic greenhouse gases. Manabe 1991 Part 1 and Part 2 (a H/T to Rabett Run for the pointer) found when modeling Antarctic effects that increased precipitation from GHG warming led to fresher surface waters, suppressing convection from warmer lower waters through a steeper halocline, and thus slightly decreasing sea surface temperatures and increasing sea ice.
Manabe's ideas weren't (at that time) widely held, as far as I can see, but he appears to have correctly predicted current observations by taking into account additional factors like halocline changes.
Really (IMO) an interesting result. Note that this means warmer sub-surface water is not cooling as much, retaining more energy, and thus the reduced convection is a positive feedback to warming - effectively insulating, keeping the energy in the oceans. And those warmer sub-surface waters continue to melt Antarctica from beneath at the edges. Something I suspect 'skeptics' will not be pointing out.
So - an unexpected observation leading to a better understanding? That's what science is about...
http://www.thestar.com/news/world/article/1275441--antarctic-sea-ice-is-increasing-is-global-warming-over
(which might be a step forward for The Star, until recently the were still in the habit of including a random denialist quote).