Characteristics of Antarctic sea ice | Increasing Antarctic sea ice | Wind and movement | Changes to sea surface temperatures | Increased precipitation | Difficulty in measurement | Climate model simulations of sea-ice trends | Summary | References | Comments |
Characteristics of Antarctic sea ice
The Antarctic continent is surrounded by seasonal, floating sea ice. This sea ice, which comprises mainly frozen sea water, with occasional icebergs from glaciers and ice shelves, covers a minimum of ~3×106 km2 in February to a maximum of ~18×106 km2 in September. This effectively doubles the size of Antarctica in the winter. Most of the summer sea ice stays in the Weddell Sea, where it is relatively protected from the ocean currents. Only about 15% of the sea ice area remains in winter.
The landmass of Antarctica means that sea ice is not formed at the pole, like it is in the Arctic. Instead, it is forced to much lower latitudes. This makes the Antarctic sea ice very different in character to the Arctic.
The Arctic regularly reaches ever smaller extents of end-of-summer minimum extents of sea ice. This changing sea ice extent is cited by the IPCC as an indicator of a warming world. However, sea ice extent is variable in Antarctica [1]. In fact, it broke a record for maximum extent in 2013 and 2014, followed by historic lows in 2016 and 2017.
However, aside from the fact that many people confuse land ice, sea ice and ice shelves, it’s important to note that there are huge differences between the Arctic and the Antarctic. The Arctic is an ocean surrounded by land. The Antarctic is land, covered by ice, surrounded by ocean. Sea ice in the Arctic is generally thick, multi-year sea ice that survives several seasons, whereas the sea ice in Antarctica largely melts away each summer. Antarctic sea ice is mostly thin (~0.6 m thick [2]), single-year sea ice. It’s also warmer, more saline and more mobile than Arctic sea ice [3].
Clearly, these two different regions will have very different responses to climate and oceanic change, and these differences will affect sea ice response. And it’s also important to remember that, while sea ice is variable in Antarctica, glaciers and ice shelves are all melting rapidly, producing large volumes of fresh water.
Increasing Antarctic sea ice
The figure below (from Ref. [4]) shows the total variability of Antarctic sea ice extent over the last 34 years. Decadal monthly averages almost overlap, and there is little change in seasonal variability.
The trend maps in the figure below show changes in sea ice extent in winter, spring, summer and autumn. The trends are mostly significant near the ice edge. Positive trends are evident in the Ross Sea, with autumn and summer negative trends mainly confined to the Bellingshausen and Amundsen seas. These trends are showing very small increases in total sea ice area and extent; the trend magnitude is approximately one third as large as the trend in decreases in the Arctic[5]. Further, the increases are strongly controlled by region (some regions are showing ever smaller sea ice extents); the Ross Sea has shown the greatest increase in sea ice extent in Antarctica.
(1979–1988 in red, 1989–1998 in blue, 1999– 2008 in gold) and a 4-year average
daily ice extent from 2009 to 2012 in black. Maps indicate ice concentration trends
(1979–2012) in (b) winter, (c) spring, (d) summer and (e) autumn (updated from
Comiso, 2010). From Vaughan et al., 2013.
The increase in total Antarctic sea ice extent 1978-2012 is slightly positive at 1.5 ± 0.3% per decade[4]. On a seasonal basis, the trends in ice extent and ice area per decade are:
| Season | Sea ice maximum extent | Sea ice-covered area |
| Winter | 1.2 ± 0.5% | 1.9 ± 0.7% |
| Spring | 1.0 ± 0.5% | 1.6 ± 0.5% |
| Summer | 2.5 ± 2.0% | 3.0 ± 2.1% |
| Autumn | 3.0 ± 2.0% | 4.4 ± 2.3% |
So, the largest trends in sea ice extent and in ice-covered area are in autumn. The trends are higher for ice area than for ice extent, indicating less open water, which may be related to changes in ice drift and wind patterns. Record highs were reached in 2013 and 2014.
While changes in Antarctic sea ice extent remains an exciting topic for further research, there are a number of reasons put forward that explain these trends.
Changes in Antarctic sea ice trends
What happened after 2014? In fact, 2017 was a historic low for Antarctic sea ice; it was 27% below average. The sharp decline from 2016-2020 was equivalent to 30 years of ice-loss in the Arctic (Carbon Brief).
The sea ice has continued to show variability, with again historic lows in 2019, and low summer extent in 2022/2023. This variability is related to the characteristics of the Antarctic sea ice pack, with historic lows potentially due to:
- natural variability
- ocean warming
- tropical and stratospheric forcing (such as contracting westerly winds).
Causes of variability
Wind and movement
Changes in atmospheric dynamics and winds are an important driver of regional sea-ice trends. Ozone and greenhouse forcings cool the Antarctic stratosphere, which increases the stratospheric vortex and tropospheric zonal winds. This results in an increase in the Southern Annular Mode [6]. Increases in the Southern Annular Mode (SAM) signify increased westerly winds [7] and a rigorous isolation and cooling of parts of the Antarctic continent [6].
Because the Arctic is a semi-enclosed ocean, there is little scope for sea ice movement. Ice in the Arctic is thicker as a result of collisions, which means that the ice will last longer. This means that much of the Arctic sea ice lasts for several seasons, leading to permanent ice cover at the pole. However, in the Antarctic, there are far fewer such constraints. The sea ice is able to move around far more freely, which means that years with larger and smaller sea-ice extents are more easily possible.
Sea ice in Antarctica floats northwards to warmer waters, where it melts away almost entirely. Changes in the winds around Antarctica therefore change ice-concentration trends around Antarctica [8] by influencing sea-ice production and melt rates [9]. The pattern of wind change is complex, but variations in winds can help to explain some of the regional patterns in sea-ice formation [8]. Where the wind blows to the north, the sea ice is blown north where it melts, resulting in increased sea-ice extent. Where the winds blow south, the sea ice is blown towards the continent, resulting in decreased sea-ice concentrations.
Polynyas are areas of persistently open water in regions where sea ice is usual. The water remains unfrozen as a result of processes that either prevent ice from forming or that move ice out of the area. Polynyas are therefore an important part of sea-ice production. An increase in the extent of polynyas in the Ross Sea from 1978 to 2008 contributed to sea ice production [2]. The resulting increased ice export accounts for a large proportion of the increased trend in ice production. Changes in wind circulation alter ice production and export in and from these polynyas.
In contrast, in 2017, a polynya opened up north of Maud Land in the Antarctic Sea Ice pack, in easternmost Weddell Sea. By mid-September 2017, the polynya, an area of open water, had grown to 12,000 km2.
Changes to sea surface temperatures
As the glaciers and ice shelves melt on the Antarctic continent, freshwater is added to the oceans. This layer of cold, fresh water on the ocean surface freezes easily [10]. When combined with increased ocean stratification due to this enhanced run off [11], sea-surface temperatures are depressed, encouraging sea-ice formation.
A recent modelling study has shown that increases in fresh meltwater flux from melting glaciers and ice caps on Antarctica under various IPCC standardised global warming scenarios offsets the decline in sea-ice area and to even further encourage the increases in sea-ice extent, especially in winter (in summer, air temperatures are too high to support significant sea-ice growth) [12].
Increased stratification has further implications. Suppression of ocean circulation overturning decreases the ocean heat flux available to melt ice, leading to an increase in net ice production[13].
Changing precipitation
Warmer air holds more moisture, and so precipitation is increasing around Antarctica [13]. Strong warming in the middle latitudes of the Southern Ocean can lead to an enhanced hydrological cycle, with enhanced evaporation and moisture content in the lower troposphere [14]. This additional moisture is transported poleward, where it results in increased precipitation. Increases in snow and rain falling onto the ocean contribute to the freshening of the ocean surface in the high latitudes of the Southern Ocean. Fresher, colder water freezes more easily, so this mechanism may contribute to the growth in area of Antarctic sea ice.
Furthermore, the increased weight of snow on the sea ice may force it deeper into the water, forming thicker sea ice when the snow refreezes. Deeper snow also insulates the ice, protecting it from melting [15].
Difficulty in measurement
Sea ice is measured by repeated images taken by satellites orbiting the Earth [16]. Passive Microwave Sensors were developed in the late 1960s, with the ability to measure sea-ice edge, surface composition and soil moisture. These measurements have been taken with approximately a daily resolution from the late 1970s onwards.
The microwave emissivity of sea ice is higher than the ocean, which means that ice-covered areas have a higher brightness temperature than the ocean [5]. However, warmer surfaces also have a high brightness temperature, so it is difficult to distinguish between cold sea ice and a warm ice-free ocean. Scientists therefore use simultaneous measurements at multiple frequencies and polarisations (the difference in emissivity between sea ice and ocean varies with frequency and polarisation) [5]. Other factors complicating the measurement of sea ice include weather interference, cloud, thin ice, and so on.
Two algorithms for estimating sea ice extent from these measurements were developed in the 1980s. The ‘Bootstrap’ algorithm is one of the most widely used ice-concentration products, and forms the basis of the observations of sea ice made in the IPCC reports.
A change in the inter-calibration across two different sensors on successive satellites caused a substantial change in the long-term trend in sea-ice extent[5]. There is apparently an error in either the current dataset or the one used prior to the mid-2000s. The authors of this particular study suggest that observations should be re-examined to determine the sensitivity of observations to this change in the dataset.
Climate model simulations of sea-ice trends
Climate models simulate a decline in ice extent, thickness and volume in Antarctica. Equilibrium models cannot currently reproduce trends in Antarctic sea ice variability [17]. Virtually all equilibrium climate models simulate a strong decrease in the area of sea ice [18]. This may be because global climate models do not currently incorporate ice-shelf / -sheet/ -climate interactions. Basal melt from ice shelves is therefore disregarded. These equilbruim models may give an idea of what may eventually happen. Simulations with models that do include these interactions, particularly simulating the effect of extra freshwater from melting glaciers and ice caps, do simulate growths in Antarctic sea ice [10, 12].
Transient climate models are more able to capture the transient response of sea ice to changes in the winds. A modelling study by Marshall et al. [19] showed that changes in the winds tend to push the ice edge northwards, increasing ice extent. These winds also push the ocean surface northwards too, which effectively brings warmer water to the surface and eventually counters the increasing sea ice trend after a few decades. These transient models show that not enough time has elapsed for the equilibrium response to be achieved. We may well see the trends reversing in a few decades.
Summary
Antarctica is a unique environment, and the complex interactions between ice, ocean and atmosphere have led to a unique set of circumstances that have resulted in sea ice growth. It may be explained by many factors, or most probably by a combination of several. Climate change is a complex process governed by multiple feedbacks between different parts of the system; complex interactions between the melting land ice and ice shelves fringing the continent and changes in wind stress are all implicated in controlling Antarctic sea ice extent. Further, more work is required to ascertain the reliability of observations of sea ice increase given the recent discovery of an error in the algorithm used to quantify and map sea ice over the last few decades.
Its is really helpful and you can find out what you need to know
You are saying sea ice is increasing in the sea while ice on the Antarctica continent is decreasing. How is it logical to come to this conclusion that ice is decreasing where it is colder (on the continent) and warmer (on the sea)?
Although this site was posted in 2015, in many ways ; trends of recent years make it out of date:
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Antarctica in recent years has Sea Ice that substantively extends into the melt season and the Ice thickness is in excess of a Metre. Most of the Bases NOW have major logistical problems of supply because the Ice “does NOT retreat” as in past years and being “of greater thickness” the Icebreakers cannot penetrate such a thickness. Currently, there is a review by some Countries as to the possible relocation of Antarctic Bases and most Countries plan to acquire larger Icebreaker Ships.
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It is common across many sites, to play down the magnitude of Cooling. The “Ship of Fools” AGW expedition to prove Melt / Warming agenda ; shows how Science has also become too Political…
I would dispute that the article is out of date. Research in Antarctic sea ice is on going and there are ever more interesting publications on this subject. However, this focused research has yet to find persistent evidence of a systematic cooling cause of the sea-ice growth. Rather, they find that cooler sea surface temperatures are related to variations in wind strength, increased land-ice and ice-shelf melt and intrinsic variablity (e.g., see this recently publshed article on the intrinsic variability in Antarctic sea ice). Most models predict that this increase in sea ice will be relatively short-lived and will be reversed over coming decades. Further,do not forget the many other indices indicating widespread glacier recession on the Antarctic Peninsula and West Antarctic; glaciers are thinning and receding, ice shelves are retreating and despite increased accumulation, glaciers exhibit a persistent negative mass balance. Ice core records also show evidence of surface temperature warming in these places.
Climate change in Antarctica is complex, with the Circumpolar Vortex causing warming in some places and cooling in others – for example, read about cooling in East Antarctica here. However, this cooling is offset by strong melting and recession in West Antarctica and the Antarctic Peninsula.
It is out of date now, though. Sea ice was growing but is now shrinking again.
It’s booming now! The alarmists will have to get a real job: https://nsidc.org/arcticseaicenews/antarctic-daily-image-update/
Alarmists? Showing data is not alarmist. The people you say should get real jobs already have “real jobs” by studying ice coverage the reasons why it is changing.
It’s not “booming” – sea ice extent decline from 2015-2017 in the Antarctic was faster than in the Arctic over the same period.
In 2017, sea ice extent in the Antarctic reached a record low in the 40-year satellite record – both on an average annual and lowest month basis.
https://www.pnas.org/content/116/29/14414
So nothing has changed in forever. The earth has been warming since the ice age… and the only time data shows it speeding up is when Obama changed the low temp reading from boats who’s temp probes were in the intake tubes(he said were in the engine rooms) How ever his theory would mean that the high temps should also have been changed by 2 degrees and there is no logic behind changing only the low temp readings. This now shows a rapid spike in warming. Thats the only data we have showing increase in warming out of the ordinary. Sorry but not sorry. And we tested the theory here of the temp probes and 99.6% of the test showed identical temp of direct ocean reading versus temp probe in the intake tubes(and those differnces were .6 degrees avg, not 2 degrees). Do the science yourself or just believe those who need funding. Up to you.
Why do you leave up outdated information? At the top of the page, it states that the information was updated in 2021, when it clearly was not, as Antarctic sea ice had been shrinking then. All you’re doing is providing ammunition for the internet’s cesspool of misinformation.
this page has now been updated, thank you for highlighting. Please bear in mind this website is maintained largely by volunteers with full time positions and there is a lot of content to maintain; feel free to volunteer your services!
Is there any data on the annual variation in ice shelf thickness due to bottom side melting and re-freezing? The recent ice shelf mass loss data I have seen (Rignot E et al 2013 and Paolo FS et al 2015) do not report any annual variations. I would be interested to know how much of the summer bottom melting is recovered in the winter, if any. In other words, does the ice shelf outbound of the grounding point thicken on the bottom during the winter and by how much. As a practical engineering question: if you drilled down through the ice shelf just outbound of the grounding point during the summer (e.g. WISSARD) would you have to drill deeper in the winter to keep the hole open, assuming that you could keep the whole open at all during the winter by continuous “hot water” drilling?
Really enjoyed your article. Excellent data summary. Thank you, really.
Noticed that both in your summary and in your reply to comments you mentioned that the Antarctic is a “complex” system. I have also noticed the use of such language in other articles regarding the Antarctic by other authors. I only wish that researchers would use that same scientifically humble tone and terminology when discussing the Arctic. Anytime there is Arctic warming, everyone screams “global warming from people, no doubt, next topic” and anytime there is Antarctic cooling everyone says “well it is complex….who really knows, we need to study it more”. As a scientist and a person who does believe we have to take care of our planet I think the environmental cause is set back thru both purposeful as well as accidental bias, especially thru language.
Very well said. I am currently reviewing the coming conjunction between a grand solar minimum, PDO, AMO and La Niña. Historical data appears to point to the potential for longer and colder winters starting last year through the next decade. Just as everyone and their dog is screaming global warming I will watch with interest as deep cooling is going to be explained away as a product of global warming.
Interesting stuff for sure. Folk always go on about the Artic and climate change but very few mention the Antarctic and what is going on there. I wonder why? Maybe it doesn’t suit the narrative of the climate change warriors?
Not convinced at all about climate change. I am more inclined to this that this is a natural event with the earth changing orbit or axis slightly. There is of course solar activity from the sun.
Amazingly, no mention by climate folk about the volcano that has been erupting in the Canary Islands for 6 weeks now. I wonder how much gas the volcano has spewed out in to the atmosphere? Probably more than mankind?
Do these climate warriors really think that man can change the course of the earth? If they do, that is for the birds in my opinion.
Hi Craig,
Currently there is a greater amount of research focused on the Arctic region in terms of sea ice (I am assuming this is what you are focussing on given your comment on this page) compared to Antarctic sea ice due to the rate of change being more significant. The Antarctic sea ice responds to a series of more complex systems and therefore it is not a simple yes it is changing due to climate change, whereas there has been a direct relationship between rising temperatures and the decline in sea ice in the Arctic year on year. Your idea about it not fitting in with the narrative of climate change warriors is simply not true. In fact there are many studies that show that some regions of Antarctic sea ice are in fact growing, as aforementioned though, sea ice in the Antarctic region is complex and is not completely responding to just climate change.
The gas emitted from a volcanic eruption is large however anthropogenic activity is also pumping out very high concentrations every day. In terms of climate, the Palma volcano is unlikely to have any major implications as it isn’t very strong at the moment. The volcanic dust and aerosols are required to reach the stratosphere before it can cause changes to our climate system which it currently is not doing.
Thanks,
Laura
Hi Laura,
many people, like Craig, are confused about Climate Change interpretation. I am the most confused overall person))
Let me rephrase Craig’s concern: “why politicians, activists and scientists are concentrating on the human’s impact ONLY, when the nature is contributing, if not equal, a significant destruction and impact on the climate change?”
Why IPCC reported in 2021 the following:
“It is very likely that human influence has
contributed to the observed surface melting of the Greenland Ice Sheet over the past two decades, but there is only limited evidence, with medium agreement, of human influence on the Antarctic Ice Sheet mass loss.” (A.1.5, page SPM 6)
To me it means that it is only humans are driving the climate and the nature is sleeping at the driving wheel. Thus, to the Craig’s comment and to the thoughts of millions, it is very simple: Arctic’s ice loss IS SIMPLE, it is due to human impact. Antarctic’s ice loss or growth is complicated, due to human’s impact is not clear yet. THUS, it is ONLY about anthropogenic component.
What am I missing?
Hi Alex,
Thanks for the comment, don’t worry climate change is very confusing to many people.
Yes so the IPCC reports that because the melting components of the Greenland Ice Sheet is more directly influenced by changes in the climate system, for example surface melt is more of a dominant control in the Arctic than in the Antarctic.
The reasons why Antarctic ice loss is more complex is because there are more factors controlling the ice loss such as changes to oceanic and atmospheric systems which requires more research to understand fully, and that is why there is only a medium agreement.
Hopefully this makes it more clear?
Check out these pages to see the difference in ice melt in Antarctica and Greenland: https://www.antarcticglaciers.org/glaciers-and-climate/changing-greenland-ice-sheet/greenland-ice-sheet/ and https://www.antarcticglaciers.org/glaciers-and-climate/changing-antarctica/
Thanks!
Laura
An excellent article, even though published some six years ago I find this all facinating, how Antarctica is deemed as “complex” vs the Arctic which is “our fault”.
The earth’s climate is and has always been cyclic. The only reason we have / had low CO2 levels in the first place was the effects of the last ice age, something we’re still climbing out of – barring the slight regression in the middle ages through to the mid-1800’s where we had the “little ice age”.
I was always taught that statistics are only meaningful if you have a broad enough stream of data, and having 180 years-worth of records vs 4.3-ish-billion years of planet is not enough to offer a proper statistical model of how the climate is likely to go. You only need to be a fraction of a percent different and you’ll get a dramatically different result from your computer model.
The human race is it’s own enemy through it’s so called intelligence “we must stop climate change” they say, well King Canute proved that we cannot control the tides, nor the weather with his documented “experiment” where his throne was placed at the sea’s edge and he commanded the tide to go back – it didn’t of course, and he showed that people cannot control what the planet does.
What we can do is (a) stop polluting it, and (b) stop/reverse breeding trends.
At COP26 in Glasgow, we hear India aim for Carbon Neutral by 2070. Well, if we keep breeding as a species as we are now, with the annual rate of increase, there will be another 4.3Billion people adding to emissions by 2070. All of the reductions spoken of today will be negated by the increase in population.
This is the elephant in the room that nobody dare mention. Tell people to stop having children, it’ll never do.
The whole “Climate Change” thing has been hijacked by the media and activists who, to be fair, do not have a clue, but love the sound of their own voices spouting soundbites. It is to the detriment of the fine work done by the scientists observing what’s really happening in the Antarctic, as well as the Arctic, regions, in fact across the planet.
What we have to do in reality is hark back to our ancestors, move, adapt, or die. Accept that the planet is going to get warmer, CO2 levels will increase, and plants will benefit from the increase in “feed”.
Our air is cleaner than it has been for decades, we (mostly) have clean water, we (mostly) have medicine, we have no brains.
Laura
Prove the Atrtic is more substantial than the Antartic.
Should be All inclusive.
Spoken as a ticket holder on a planet participating in a ride on a rock orbiting a sun in a universe hurtling through space that has been around approximately 5 billion years. Current ticket holders enjoy a 75+ Year life span average.. U.S..
I’ve spent probably the last four years comparing core sample temperature to CO2 and I havent seen one explanation as to why, on several occasions, CO2 spiked much higher than present day and the temperature dropped like a brick, there are also several occasions where CO2 levels dropped and temperature increased dramatically so surely concentrating on CO2 as a driver is flawed without answers to those moments.
Secondly, where I live, 1500 years ago the water levels were several miles further in land than they are today and 10000 years ago the mountains were covered due to fossils records and such like in the rock beds, historically this rise and fall is easy to see in core samples so why the panic when the environment is following a pattern. You only have to see that the earth has been iceless for more than 85% of its life to understand its normal state is without ice, humans wouldn’t exist if it wasn’t for that single fact, I see climate change alarmists as a man on some rail tracks trying to stop a train with a fish especially when there is no answer to point one.
I wish all the doomsday scientists would go find another job and stop their crazy solutions for the planet. If doomsday is going to come I’m fine with it. I’m not fine with man’s crazy solutions and political machinations to destroy whatever quality of life we have while living on this planet. It will be man’s solutions that will destroy this planet.
Ah, reading this thread (or any climate alarmism argument) makes me wonder how much better off we all might be if only we could replace (misplaced) confidence with (actual) competence.
Since I’ve lived in the same home for 34yrs and I’ve watched the sun go from coming up straight through my kitchen window(which would make the sun due east) on the summer solstice in 1990, but on the summer solstice of 2023 you had to walk all the way from the back of the house to the front porch(40ft), then another 8ft out onto the front porch(48ft total) and look to the NE at over a 30* angle to see the sun come up.
Well since I’ve been a finish carpenter for over 40yrs I’m pretty good at judging angles and if you’d stand in my kitchen looking out the window it’s well over a 45* angle farther in the northern hemsphere that the sun came up in 2023 compared to where it came up in 1990! But this is something they aren’t telling anyone, they’re keeping it very quite, after all it’d ruin or seriously put into doubt the climate change narrative!
This is the reason the Northern Pole is melting and Antarticia is putting on more ice cap!
Tēnā koe Dale E hoa, from Aotearoa NZ
What part of anthropogenic climate change do you take issue with precisely? Is it the greenhouse effect? You don’t understand how blanketing gasses can entrap heat like a solid blanket?
You may test this yourself quiet easily my dear. Go buy two bottles of water, ensure they are identical and the same brand except one still one sparkling. Leave them in sun for a bit then measure the temperature.
The bottle with CO2 will retain more heat. Not only will it be warmer but it will remain warmer longer also, as carbon dioxide is a better insulator than air.
Make sense? Any Pātai (questions or concerns)?
Ngā manaakitanga
Sorry, did you really understood what Dale said? Seems like you didnt