Arguments
Is Antarctica losing or gaining ice?
What the science says...
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Satellites measure Antarctica is gaining sea ice but losing land ice at an accelerating rate which has implications for sea level rise. |
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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
I suspect the "water lift" effect might come to dominate in coming years. The underside of the ice shelfs slope upward from their grounding line to the seaward edge of the ice. As this ceiling melts under the influence of slightly warmed sea water, it freshens the water which being lighter, flows oceanward along this upsloping ceiling of ice. As the grounding line becomes deeper and deeper as the ice melts back under a retrograde slope of the ocean bottom, this effect should increase. Of course as the freshened water flows up and out on the surface of the ocean, it pulls sea water in under the ice. An added effect is that the ice melts at lower temperatures at depth so the fresher water may be "super cooled" with respect to the shallow water where it exits the ice shelf. This could be an added explanation for the increase in sea ice as this very cold, somewhat fresher water then comes in contact with Antarctic Night air. These currents may also be pushing the ice outward, opening leads that then freeze over.
Awesome blog. I enjoyed reading your articles. This is truly a great read for me. I have bookmarked it and I am looking forward to reading new articles. Keep up the good work!
"Satellites measure Antarctica is gaining sea ice but losing land ice at an accelerating rate which has implications for sea level rise."
This "argument" is clearly wrong. Antartica is gaining land ice mass and sea Ice. This should be corrected if this site claims to offer science as answers.
http://www.nasa.gov/feature/goddard/nasa-study-mass-gains-of-antarctic-ice-sheet-greater-than-losses
"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."
There is nothing in that study to suggest that he ice gain that has been occurring for 10,000 years has stopped.
The Science has shown that Antarctica is gaining ice. Clinging to this false claim that the "science says" Antarctica is losing land ice shows poor alligiance to science.
There are a whole bunch of studies that show the Antarctic (land-based) ice sheet is losing mass versus Zwally's study that claims otherwise. Zwally's work is currently incompatible with Holocene sea level history and recent assessments of the sea level budget.
So there's a considerable volume of scientific work arguing against it. We'll just have to wait and see if Zwally's work stands up to scrutiny. If it does, we will change the text accordingly. Changing it now would be premature.
As for Antarctic sea ice, that's very interesting and very likely related to the wind trends and their effect on the polar gyres. SkS will have a new post on that in a few weeks.
Iceman
Here is the latest sea ice extent for Antarctica.
Fairly low for this time of year.
Yes there has been some increase in the maximum in recent years. But we will have to wait and see as to whether that is an ongoing increase or not.
And Rob is right, The Zwally paper is new and is an outlier result compared to other studies. Too early to assess whether it will stand or not.
That should read "Table 5" not "Table 10"
Maybe someone could help me understand. Antarctic ice? If the land ice is melting but the sea ice is increasing, don't we have two separate causes? It don't understand how you can have both with the same environment.
Anecdote: When the glacier covered Maine the plate was 200 feet below sea level. The glacier melted away ( from global warming?? ) and the land plate floated up and is now 4 feet above sea level. Or did the sea level fall because the land mass moved up. I am sure someone out there could explain this to me. please!
It seems to me when a tectonic plate looses massive amounts of weight ( ice ) in this case, it makes sense that it might move up because it is floating on magma ( or something like that ).
I also wonder about wind mills too. If our "climate" is dependent on air streams; based on earth rotation and adiabatic rise, then if we take the heat ( energy ) out of the wind we have not, will that not affect the wind currents driving our local climates?
B14
" don't we have two separate causes?" Yep. Maybe more than 2.
Sea Ice has increased a little in the last few years although mainly at the maximum in winter. This year, at the summer minimum it is rather low. Drivers of sea ice extent? Possible changes in sea water salinity, changing the freezing point of the water. Changes in the winds around Antarctica, driving more spreading of the ice and freezing over of the open water created. The wind patterns may have changed due to a combination of the current Pacific Decadal Oscillation which has now started changing, and the ozone hole allowing more sunlight to reach the surface rather than being absorbed in the stratosphere; the extra energy from this may have accelerated the winds.
In Antarctica land ice doesn't melt much - it is too cold. Rather it flows slowly to the coast and eventually breaks off as icebergs. Factors changing this? Ice sheet breakup. Floating ice sheets (not seasonal sea ice) act as buttresses, slowing the speed with which land ice can flow. Some have broken up. Grounding line retreat. This applies particularly in West Antarctica where the 'land ice' is actually sitting on the sea floor 100's and even 1-2000 meters below sea level. Sea water intrusion at the grounding line is causing some retreat of the grounding line, so that ice that was grounded ends up floating, and easier for icebergs to break off. The key here is what is happening to sea water temperatures at the base of these sheets, 100's of meters down. This in turn can depend on differences in what is happening to different currents at different depths.
Some recent research also suggests there is a critical threshold wrt the height of ice cliffs. It seems ice when it contains cracks isn't strong enough to allow ice cliffs to rise much more than 100 meters above sea level. Otherwise it breaks off. Then buoyancy of the remaining submerged ice can then break that off from the main ice cap.
Ice is way more complicated than just melting and freezing.
In reality, Arctic sea ice is at a record low and global sea ice is diminishing.
NASA LINK
NATURE LINK
NSIDC LINK
Further, Antarctic sea ice is shrinking, now statistically indistinguishable from the long-term average:
LINK, showing current extent of Antarctic sea ice
NSIDC LINK
Hi -
I have found this thread helpful to getting perspective on land and sea ice discussion. My comment is a question or request about data:
For a long time I have been trying to monitor land ice, but for the layman the information does not seem to be readily out there and updating regularly. I see this page:
https://climate.nasa.gov/vital-signs/land-ice/
However, that information has not been updated past March 2016. I've tried to dig around a bit for alterntaive sources of information and haven't so far been able to find any. I don't know if it is the function of this page to provide such information, but does anyone know of a good source that can readily be understood by non-scientists? (To get an updated reading of whether trends in Antarctica toward lower land ice are continuing).
Should this discussion be updated to account for the recent record lows in Antarctica's sea ice extent?
jlsoaz: Did you look at the National Snow & Ice Data Center's website, nsidc.org?
Hi amhartley:
Thanks for the response.
Yes, I have been to nsidc.org a fair amount, particularly this page to try to understand each Northern Hemisphere summer what is going on with greenland ice melt:
http://nsidc.org/greenland-today/
While I do like that page, I must say I have not been able to find what I am looking for there, as far as clear non-scientist-oriented data that shows land ice changes over the years, whether for the Antarctic, Greenland or other places.
The NASA site I mentioned in my post above seems to show land ice mass changes.
https://climate.nasa.gov/vital-signs/land-ice/
and it cites two sources:
https://grace.jpl.nasa.gov
https://www.nasa.gov/mission_pages/icebridge/index.html#.VDQh8UvLxd0
There seems to be (as best I can make out) a common theme to both sources that they were satellite-based systems, with IceSat gone and GRACE no longer functioning fully, and both systems seem to have scheduled replacements. (Maybe I am confused and they are one and the same system, but it seems like possibly different systems and different planned replacements).
https://en.wikipedia.org/wiki/Operation_IceBridge
https://en.wikipedia.org/wiki/ICESat-2
https://en.wikipedia.org/wiki/Gravity_Recovery_and_Climate_Experiment#GRACE_follow-on
Perhaps it is the somewhat challenging nature of the science journalism involved, but I haven't seen a single news story which gets at the important question of how important this land ice data would seem to be, that no widely-disseminated information seems to be available dating past 14 months ago, and that both sources are dependent on expensive new planned launches which we can hope won't be pushed back or cancelled, but which are still 2-3 quarters away at the least.
Perhaps the IceBridge interim plane-based system can provide data, or perhaps other countries or systems are developing data? Japan? China? NASA has literally labeled this as a "vital sign" and it does seem important, so I'm hoping to uncover if there is more reliable data out there. Perhaps I have missed something at NSIDC. Do you have a specific link in mind?