Arguments
Is Antarctica losing or gaining ice?
What the science says...
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Antarctic sea ice extent has expanded at times but is currently (2023) low. In contrast, Antarctica is losing land ice at an accelerating rate and that has serious 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)
At a glance
Who discovered the great, South Pole-straddling continent of Antarctica? According to the National Geographic, Captain Cook came within an estimated 80 miles of it in the late 1700s, but the three first 'official' discoveries all took place in 1820 by Russian, British and American teams of seafarers respectively.
Since that initial discovery, Antarctica has attracted and inspired researchers and explorers alike. It's a challenging place, fringed by sea-ice that, unlike the Arctic, has not steadily declined but whose extent fluctuates on a seasonal basis: it's currently (February 2023) at a very low coverage, but it can and does recover from such dips. Antarctic sea-ice is no great problem, with the exception of albedo-loss in low extent years: if it all melted, it would have no effect on global sea-levels. It's the stuff on land we need to focus upon.
The land of Antarctica is a continent in two parts, divided by the 2,000 m high Transantarctic Mountains. The two parts differ in so many respects that they need to be considered separately. East Antarctica, that includes the South Pole, has the far greater landmass out of the two, some 4,000 by 2,500 kilometres in size. Although its massive ice-sheet, mostly grounded above sea level, would cause 52 metres of sea level rise if it completely melted, so far it has remained relatively stable. Snow accumulation seems to be keeping in step with any peripheral melting.
In contrast, in the absence of ice, West Antarctica would consist of islands of various sizes plus the West Antarctic Peninsula, a long mountainous arm pointing northwards towards the tip of South America. The ice sheet overlying this mixed topography is therefore grounded below sea level in many places and that's what makes it far more prone to melting as the oceans warm up. Currently, the ice-sheet is buttressed by the huge ice-shelves that surround it, extending out to sea. These slow down the glaciers that drain the ice-sheet seawards.
The risk in West Antarctica is that these shelves will break up and then there will be nothing to hold back those glaciers. This has already happened along the West Antarctic Peninsula: in 1998-2002 much of the Larsen B ice-shelf collapsed. On Western Antarctica's west coast, the ice-sheet buttressing the Thwaites Glacier – a huge body of ice with a similar surface area to the UK - is a major cause for concern. The glacier, grounded 1,000 metres below sea level, is retreating quickly. If it all melted, that would raise global sea levels by 65 centimetres.
Such processes are happening right now and may not be stoppable - they certainly will not be if our CO2 emissions continue apace. But there’s another number to consider: 615 ppm. That is the CO2 level beneath which East Antarctica’s main ice sheet behaves in a mostly stable fashion. Go above that figure and the opposite occurs - major instability. And through our emissions, we’ve gone more than a third of the way there (320 to 420 ppm) since 1965. If we don’t curb those emissions, we’ll cross that line in well under a century.
Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!
Further details
Arguments that we needn't worry about loss of ice in the Antarctic because sea ice is growing or even that sea ice in the Antarctic disproves that global warming is a real concern hinge on confusion about differences between sea and land ice, and what our best information about Antarctic ice tells us.
As well, the trend in Antarctic sea ice is not a permanent feature, as we'll see. But let's look at the main issues first.
- Sea ice doesn't play a role in sea level rise or fall.
- Melting land ice contributes to sea level rise.
- The net, total behavior of all ice in the Antarctic is causing a significant and accelerating rise in sea level.
Antarctic sea ice is ice which forms in salt water mostly during winter months. When sea ice melts, sea level does not change.
Antarctic land ice is the ice which has accumulated over thousands of years in Antarctica by snowfall. This land ice is stored ocean water that once fell as precipitation. When this ice melts, the resulting water returns to the ocean, raising sea level.
What's up with Antarctic sea ice?
At both poles, sea ice grows and shrinks on an annual basis. While the maximum amount of cover varies from year to year, there is no effect on sea level due to this cyclic process.
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
Trends in Antarctic sea ice are easily deceptive. For many years, Antarctic sea was increasing overall, but that shows signs of changing as ice extent has sharply declined more recently. Meanwhile, what's the relationship of sea ice to our activities? Ironically, plausible reasons for change may be of our own making:
- Ozone levels over Antarctica have dropped causing stratospheric cooling and increasing winds which lead to more areas of open water that can be frozen (Gillett & Thompson 2003, Thompson & Solomon 2002, Turner et al. 2009).
- 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, Bintanja 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.
Against those factors, we continue to search for final answers to why certain areas of Antarctic sea ice grew over the past few decades (Turner et al. 2015).
More lately, sea ice in southern latitudes has shown a precipitous year-on-year decline (Parkinson 2019). While there's a remaining net increase in annual high point sea ice, the total increase has been sharply reduced and continues to decline.
How is Antarctic land ice doing?
We've seen that Antarctic sea ice is irrelevant to the main problem we're facing with overall loss of ice in the Antarctic: rising sea level. That leaves land ice to consider.
Figure 2: Total Antarctic land ice changes and approximate sea level contributions using a combination of different measurement techniques (IMBIE, 2017). Shaded areas represent measurement uncertainty.
Estimates of recent changes in Antarctic land ice (Figure 2) show an increasing contribution to sea level. Between 1992 and 2017, the Antarctic Ice Sheets overall lost 2,720 giga-tonnes (Gt) or 2,720,000,000,000 tonnes into the oceans, at an average rate of 108 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 0.3 mm/yr.
There is variation between regions within Antarctica as can be seen in Figure 2. The West Antarctic Ice Sheet and the Antarctic Peninsula Ice Sheet are losing a lot of ice mass, at an overall increasing rate. The East Antarctic Ice Sheet has grown slightly over the period shown. The net result is a massive loss of ice. However, under a high-emissions scenario, ice-loss from the East Antarctic ice-sheet is expected to be a much greater in the decades after 2100, as reported recently by Stokes et al. (2022). That’s a scenario we must avoid at all costs.
Takeaway
Independent data from multiple measurement techniques (explained here) show the same thing: Antarctica is losing land ice as a whole and these losses are accelerating. Meanwhile, Antarctic sea ice is irrelevant to what's important about Antarctic ice in general.
Last updated on 14 February 2023 by John Mason. View Archives
Worth noting that there is now comprehensive review published here concluding "it lost 2,720 ± 1,390 billion tonnes of ice between 1992 and 2017, which corresponds to an increase in mean sea level of 7.6 ± 3.9 millimetres (errors are one standard deviation). "
More importantly, it discusses the reasons behind the different estimates and why the variation, especially with ICESet altimetry data.
Daniel Bailey, thanks for that summary, that was helpful.
[DB] You're very welcome! I added some additional sources and explanatory texts to my comment above.
Anyone hear anything about how much of the melting West Antarctic land ice is due to geothermal/volcanism versus the warming climate?
Ed @478, take a look at the comments at this SkS post from 2014: Ice Picks: Five pieces of ice news...
You may want to look at the comments at a RealClimate post from the same time. Specifically this one (#179).
The upshot is that not much of the melting in West Antarctica is due to geothermal heat flux.
Thanks David. It's difficult to find any hard quantitative data. I don't see much in the references you provide.
I did did a quick search and found a few more articles, one an actual journal paper with more recent information:
https://phys.org/news/2015-07-surprisingly-high-geothermal-beneath-west.html
https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1002/2017JB014423
PS: It's important to note that according to the above sources glacial meltwater isn't the only contribution of the geothermally warm area that affects sea level. The meltwater essentially lubricates the accelerated motion of the ice flowing into the ocean.
[DB] From Cazenave et al 2018, the various contributions to SLR from 1993-2015:
And from 2005-2015:
The Realclimate comment does the calculation to show how small the geothermal component is, even with ridiculously unphysical assumptions. Furthermore, if you look at the references behind your links, you will note the important comment that geothermal flux is not increasing - there are physical constraints around the rock properties in play. When you are looking at change in Antarctica, geothermal influence isnt important.
The biggest player in Antarctica is the loss of the buttressing ice shelves undermined by warming adjacent ocean (see also here), which speeds glacial loss.
The influence of near-surface winds, in particular steered by extratropical cyclones or anti-cyclones, has recently received renewed attension. As much of the sea-ice is guided by near-surface winds, anomalously strong offshore winds can act to reduce the seasonal retreat of sea ice (it can also act the other way round). This influence of the wind as a mechanical driver of changes in sea-ice extend is comparable to the associated thermodynamic influence via warm and cold-air advection onshore/offshore Antarctica (1).
Regional changes in the frequencies and intensities of different weather types, weather patterns, the associated storm tracks and related phenomena, like weather fronts, to a global-scale warming is highly complex and display no homogeneous increase. The local anomalies of the sea-ice extend during the melt season is even coupled to anomalous winds during the previous sea-ice growth season, which affects the sea-ice growth rate and acts as initial condition for the anomalies seen in sea-ice extend during the next season. The sea-ice extend anomalies are not directly/instantaneously connected in space and time to wind anomalies (2,3,4).
Nonetheless, studies have found trends in number of extratropical cyclones and anticyclones that agree with those seen in Antarctica sea-ice extend, across space and time and not suprisingly, the changes in the frequency of weather systems and related wind exhibit high spatial variability (4).
Assuming a homogenous decrease of sea ice in response to global warming is a clear over simplification as the intermediate scale, the weather scale, and its response to a hemispheric-wide mean warming trends is highly non-linear in space and time. There is clear tendency by critics to discount/ignore the influence of the wind as a mechanical driver underlying the observed sea-ice trends and focus purely on a simplified thermodynamic local response.
Literature:
(1) Holland, P. R., & Kwok, R. (2012). Wind-driven trends in Antarctic sea ice drift. Nature Geoscience, 5, 872–875. https://doi.org/10.1038/ngeo1627
(2) Holland, M. M., Landrum, L., Raphael, M., & Stammerjohn, S. (2017). Springtime winds drive Ross sea ice variability and change in the following autumn. Nature Communications, 8, 731. https://doi.org/10.1038/s41467-017-00820-0
(3) Holland, P. R. (2014). The seasonality of Antarctic sea ice trends. Geophysical Research Letters, 41, 4230–4237. https://doi.org/10.1002/2014GL060172
(4) Schemm, S. (2018). Regional trends in weather systems help explain Antarctic sea ice trends. Geophysical Research Letters, 45. https://doi.org/10.1029/2018GL079109
It seems the melting of the land ice of the west coast has to be found in the volcanoes that have been discovered not in the human activity. A 2017 study claimed to have found 138 volcanoes, of which 91 were previously unknown. See :
https://sp.lyellcollection.org/content/early/2017/05/26/SP461.7
Roque @484 ,
you can get more information from the University of Washington, which studies this area.
If I understand it correctly, there was no suggestion that the 91 previously unknown volcanoes were new (i.e. producing additional new heat to melt the overlying ice). So presumably all the local volcanoes have been producing heat for thousands of years ~ not much changed over the 5-6000 years demonstrated in the glacial records there.
But do note that there is a possibility that, as AGW causes more melting, there will be less weight of ice pressing down on the volcanic areas . . . and the volcanoes might therefore be able to increase their activity in the future (contributing to even faster ice melt & sea-level rise over an uncertain period). This is just one more of the uncertainties about rate of sea-level rise over the next century or more.
Vulcanism has been present in Antarctica for well over 50 million years.
The ice sheet there formed 34 million years ago, and persisted since, in spite of that vulcanism. A subglacial heat mantle plume would have produced detectable subglacial drainage and melting events. None has been detected for the Pine Island Glacier and the adjacent Thwaites Glacier has proven largely insensitive to the presence of such a mantle heat source:
And
The heat coming from the geothermal activities under the ice is not a whole lot more than that coming from a dormant volcano.
People walk on dormant volcanoes. Trees grow on them.
In Antarctica, ice forms on them.
Marie Byrd Land
The volcanic heat plume mentioned under the ice of a portion of Antarctica is fossil heat; its last activity predates the formation of the Antarctic Ice Sheet (itself more than 34 million years old).
So the ice in the area formed anyway, in spite of the supposed "volcano".
Influence of a West Antarctic mantle plume on ice sheet basal conditions
I believe that there are observable changes in the natural environment (such as ice-caps melting and sea-level changes), and that these are due to climate change. But I think denial of such things is probably bad science, and promoted by bad skeptics. It's not fair to characterise all "skeptics" as all having such beliefs.
The better scientific case against "climate change" is that it's not human causes, but natural causes, that are responsible for the bulk or entirety of these changes. The climate changes naturally and always has. The true question is -what is causing that change-?
AGW promoters say CO2. "Skeptics" say natural factors such as Milankovitch cycles, solar radiation cycles, and the circumpolar vortex.
Sherwood Idso, in a 1998 paper, presents a case, based on results from eight natural experiments, that the influence of CO2 on the temperature, through the greenhouse effect is minimal - he derives an upper limit of 0.4 degrees C for a 300 to 600 ppm doubling of atmospheric CO2. Piers Corbyn also believes that the influence of CO2 on climate is minimal/insignificant.
[PS] Past climate change was most certainly from natural well-understood causes, but that is irrelevant to today because those natural causes should be cooling us. If you are a genuine skeptic try applying that to Sherwood and Corbyn and see if you can spot the errors and downright misleading information yourself.
Jesscars @487 , if you go to the well-known website WUWT [WhatsUpWithThat] you will find that "skeptics" have all sorts of beliefs about climate-change / global-warming. And these beliefs are mostly mutually contradictory.
A few hold beliefs that are quite reasonable ~ at least, for the conditions prior to the industrial-revolution / coal-burning. Others believe that the [observed & well-documented] ice-melt & sea level rise are simply not happening ~ are a hoax (from a two-century conspiracy by corrupt scientists worldwide . . . a conspiracy without even a single whistle-blower ! ) Others believe that "chemtrails" are being sprayed by the Lizard People (disguised as humans) in order to befuddle and subdue the human race . . . leading to a dictatorship by an Anti-Christ or alternatively a Marxist World Government (run by the Illuminati or similar).
Half are in complete denial CO2 has any physical effect whatsoever (other than nourishing plants). Others think the atmospheric CO2 effect is low but negligible, and that we can keep merrily burning coal/oil until it's all used up. Yet others think (despite the evidence) that all global warming/cooling comes from oceanic overturning cycles of 1400 years' duration (or whatever). Or believe that the the orbits of Jupiter & Saturn are the underlying cause of climate change . . . or that Galactic Cosmic Rays are the sole responsible factor. In short : ABCD (Anything But Carbon Dioxide) .
But what say you, Jesscars ?
# Probably simpler for you to answer here , rather than on all the other six threads you have posted in over this afternoon.
# Also, please don't bother to mention Idso & Corbyn ~ since those two gentlemen have failed at basic arithmetic.
If you semi inflate a soccer ball then put it on the floor with a weight on it , it will deform to roughly the same shape as the earth. Take the weight off and the ball becomes more of a globe shape rather than a flattened pear. When the localised weight of the Antarctic ice is removed, what happens to the rest of our connected planet . My bet is that this will give rise to a global redistribution of surface tension and an associated rise in tectonic and volcanic activity. Also possibly the weight of other continental plates will cause them to sink lower than their present position re the geoid and thus contribute to an increase in apparent sea level rise caused by continental sink. Thoughts?
Ataluma @489,
Concerning ther seismological part of your comment, a 2012 book 'Waking the Giant: How a Changing Climate Triggers Earthquakes, Tsunamis, and Volcanoes' by Bill McGuire has a CarbonBrief assessment here.
MA Rodger@490, thanks for the info re Bill McGuire. Cheers
My understanding is that the GRACE satellite shows that Antarctica was been losing mass throughout the years during which Zwally showed increases in sea ice extent. Since ice extent is a 2D measure, it can't acocunt for ice thickness the way GRACE gravity wave measurements can.
I'm not sure where to find the newest data from GRACE-FO, which llaunched in May, 2018 (I couldn't interpret it, anyway), but I am interested to see how the continent's mass has changed in recent years.
icowrich @492,
GRACE did show a loss of Antarctic ice mass 2002-16 as the NASA graphic below illustrates. We all await the GRACE-FO data (which should soon start appearing here). The numbers are now being published (here) but so far only in a form that will require a bit of processing to show the sort of data graphed out below.
Note this is all land ice. Sea ice floats so is invisible to GRACE.
The work by Zwally (that I know of) also did not concern Antarctic Sea Ice, Sea Ice Extent or otherwise. Mind, satellite data did show a small increase 1979-2015 in Antarctic Sea Ice Extent but that dramatically turned into a decrease 2015-17 - as graphed here - (usually 2 clicks to 'download your attachment').
Zwally et al (2015) concerned analysis of the land ice and the altitude of the ice surface. This showed an increase in altitude suggesting an increase in ice mass. The controversy revolved around levels of snowfall and the process of snow-compaction-into-ice as well as canculation of data uncertainties. It had some merit but obviously the GRACE data is a very strong counter-argument which makes the controversy more academic than a battle over results.
Recommended supplemental reading:
‘Extraordinary thinning’ of ice sheets revealed deep inside Antarctica by Damian Carrington, Environment, Guardian, May 16, 2019
Antarctic instability 'is spreading' by Jonathan Amos, Science & Environment, BBC News, May 16, 2019
Precipitous' fall in Antarctic sea ice since 2014 revealed by Damian Carrington, Environment, Guardian, July 1, 2019
Glacial melting in Antarctica may become irreversible by Adam Morton, Environment, Guardian, July 9, 2019
Comment 475 and its references are very helpful. Comment 452 is undoubtedly spam!
Zwally (2015) is still doing the rounds on social media, although there seems to have been much research reconciling it since. I also found the Scambos & Shuman comment, Martin‐Español et al (2017) (press release here), IMBIE (2018) highlighting the possible range of East Antarctica loss or gain, and then a couple for 2019 not directly linked in these comments so far:
The Scientific American article "What to Believe in Antarctica’s Great Ice Debate" by Shannon Hall says 'Most scientists agree that East Antarctica—unlike its western counterpart—is gaining mass in the form of snowfall or ice'. I notice that Shepherd et al agrees with that (East Antarctica subtracting 1.1 ± 0.4mm sea level rise since 1992), but Rignot at al says E Antarctica has contributed 4.4 ± 0.9 mm in the same period. All the above agree that Antarctica as a whole is losing mass (mostly from glacier flow into the sea), but one study says three times more than the other.
How can sea ice increase and land ice decrease at the same time?
[DB] Both Arctic sea ice and Antarctic sea ice daily extents are currently well-below the long term average of all decades prior since 1979. Land-based ice continues to be lost with losses increasing in recent decades. See here, here, here, here and here.
Hi,
How did you get the impression that sea ice is increasing?
Hi. While the current situation has seaice decreasing, it is entirely possibly to have increased melt from ice sheet and increasing sea ice. This was the situation a few years ago. Drivers for both sea and land ice are different between Antarctica and Arctic due to the major geogeographic difference - Antarctica is a continent, 2000m high at pole, surrounded entirely by ocean whereas the arctic is a landlocked sea. Sea ice in the Antarctic responds to a complex set of factors which have quite a lot variability. See this post for more detail. We could easily have a return to increasing seaice. However, the very long term trend is likely to be reduction as the warming sea temperature dominate, over wind-driven dispersal and decreased saliinity. The decrease in ozone loss should also reduce wind dispersal.
Hi,
This myth is a little old now. Five or more years ago for a few years there was relatively high sea ice in the Antarctic. The record is not very long, only since 1979. Deniers claimed that since sea ice in the Antarctic was high, warming could not be occuring. In the past four or five years the ice area in the Antarctic has collapsed to the lowest in the record. This myth has gone out of fashion since now Antarctic sea ice is low. Land ice is also melting in the Antarctic.
To answer your question: It is believed that sea ice area in the Antarctic is strongly affected by winds. If there are a lot of offshore winds then new ice freezes near shore as existing ice is blown out to sea. Strong winds thus increase sea ice area. Around 2010 the winds in the Antarctic were stronger offshore than they had been before that time. It is not completely clear why the winds were stronger. It may have been due to natural variation or it may have been due to some climate change affect or the result of the ozone hole affecting wind. Now the winds are more similar to what they used to be and warmer ocean temperatures are melting more sea ice.
The land ice in the Antarctic is most strongly affected by the temperature of the ocean. As AGW warms the ocean the land ice melts faster where it enters the sea. This affect is slow to start because the ocean is warmed in the Tropics and then currents slowly move the warm water all the way to the Antarctic. Currently, especially in West Antarctica, the ocean is warming and melting the great ice sheet. The warmer ocean does not affect the sea ice as much as the wind did.
So if you have strong offshore winds the sea ice increases while increasing ocean temperatures melt the ice sheet. In general, the ice sheet is more important since if it melts hundreds of millions of people will be flooded, including much of Florida and other coastal states. Sea ice does not affect sea level.
There are more complications if you look more in depth. Warmer air causes snowfall to increase. If snowfall increases enough the East Antarctic ice sheet (which is much bigger than the West Antarctic ice sheet) may increase in size even as the edges melt faster from the warmer ocean. It is difficult to measure the exact balance of the East Ice sheet because it is so remote and cold and big. An error of a few centimeters per year would be significant.
Wunderground (weather blog) has had a series of blogs on measuring the snowfall in East Antarctic here is the last one. Currently it is believed that the East Ice Sheet is very slowly losing mass but that could change (either up or down) depending on how much CO2 is eventually emitted.
How can land ice be decreasing, while sea ice is increasing at the same time?
[PS] Several commentators have already answered. See above.