Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Donate

Twitter Facebook YouTube Pinterest

RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

Keep me logged in
New? Register here
Forgot your password?

Latest Posts


How does Arctic sea ice loss compare to Antarctic sea ice gain?

What the science says...

Select a level... Basic Intermediate

Arctic sea ice loss is three times greater than Antarctic sea ice gain.

Climate Myth...

Arctic sea ice loss is matched by Antarctic sea ice gain
In fact, the global sea-ice record shows virtually no change throughout the past 30 years, because the quite rapid loss of Arctic sea ice since the satellites were watching has been matched by a near-equally rapid gain of Antarctic sea ice. Indeed, when the summer extent of Arctic sea ice reached its lowest point in the 30-year record in mid-September 2007, just three weeks later the Antarctic sea extent reached a 30-year record high. The record low was widely reported; the corresponding record high was almost entirely unreported. (Chris Monckton)

Have Arctic ice losses truly been balanced by Antarctic gains? The first point to clarify is that we are talking about floating sea ice, not to be confused with land ice. Land ice at both poles and in glaciers around the world is sliding into the ocean at an accelerating rate. This net loss of land ice is contributing to sea level rise.

However, Monckton is clearly referring to sea ice. The rapid decline of Arctic sea ice has indeed coincided with an increase in Antarctic sea ice. But do these two opposite trends cancel out as Monckton suggests? In reality, the upward Antarctic trend is only slight compared to the plummeting Arctic trend. Tamino has crunched the numbers and found the Arctic trend is in fact more than three times faster than the Antarctic one. The net result is a statistically significant global decrease of more than a million km2 or a few percent – would you agree with Monckton that this is “virtually no change”?

Global sea ice since 1979

Figure 1: Global sea ice extent since 1979. (Image source: Tamino. Data is from US National Snow and Ice Data Center.)

global sea ice extent

Figure 2: National Snow and Ice Data Center (NSIDC) Antarctic, Arctic, and global (sum of the two) sea ice extents with linear trends.  The data is smoothed with a 12-month running average.

Sea ice area data shows the same thing as extent data.

Summer and Winter, Apples and Oranges

Monckton compares the Arctic summer to the Antarctic winter, not the most appropriate comparison. Sea ice grows and shrinks seasonally because polar latitudes have vastly more daylight hours in summer than in winter. When ice melts, it makes the surface less reflective and amplifies the warming (as is currently occurring in the Arctic), but this effect can only make a difference when the Sun is up. Thus the most important time of year for sea ice is its annual minimum which occurs at the end of the summer: September in the Arctic but February in the Antarctic.

So how do the two compare?

Minimum sea ice extent since 1979 in the Arctic and Antarctic

Figure 3: Minimum sea ice extent since 1979 in the Arctic and Antarctic. (Image source: James Hansen. Data is from US National Snow and Ice Data Center.)

While the summer Arctic has lost an extent of about 2.5 million km2 (equivalent to the area of Western Australia), the summer Antarctic growth is only 0.3 million km2 (about the size of Victoria). Even that slight upward trend is less than the year-to-year variability; although 2003 and 2008 tied for the highest February extent, 2006 was third lowest. Again, the real world contradicts Monckton’s assertion that changes in the Arctic are being balanced out by the Antarctic.

The Third Dimension

Furthermore, Monckton fails to mention that Arctic sea ice is not only shrinking in extent but also has been thinning rapidly. Although its lowest extent was in 2007, its volume has continued declining since then, hitting another record low in 2010:

Arctic sea ice volume since 1979

Figure 4: Arctic sea ice volume since 1979. (Image source: Wikipedia. Based on data from University of Washington Polar Science Center.)

The volume data is supported by a sharp decline in thick multiyear ice (Figure 5).


Figure 5: NSIDC Arctic sea ice age from 1983 through 2011 (Source)

Meanwhile there has been a slight increase in Antarctic sea ice volume, but only by about 5,000 km3 (insufficient to offset the Arctic decline shown in Figure 4), and most of it in a few years at the start of the record.

The Polar Prognosis

As thinner and younger ice is easier to melt, the rapid Arctic melt is set to continue; ice-free summers are now probably inevitable. In contrast, the Antarctic increase is occurring despite the warming of the Southern Ocean and is expected to reverse as the warming continues. Antarctic sea ice is just a distraction from the accelerating losses from ice sheets and the looming specter of a sea-ice-free Arctic.

Last updated on 27 November 2011 by dana1981. View Archives

Printable Version  |  Offline PDF Version  |  Link to this page


Comments 1 to 10:

  1. Hope I've got the right thread here. I recently had an online discussion with a 'skeptic' in which he claimed that 'skeptics' only talk about sea ice extent because the measurements for volume are unreliable. I duly did my research and, as I expected, his criticisms were invalid. Measurements are taken by satellite, submarine, and by scientists on the ground,then extrapolated for the whole area of coverage. From what I read the results are reliable, in fact slightly overestimating the thickness of the ice. However, two days ago I read a newspaper article in which the chief scientist at the met office was quoted as saying that the thickness of arctic sea ice is not known with any confidence.
    This has left me slightly baffled and perplexed. I just wondered if anyone would like to try and shine a light on this for me. Thanks.

    [DB] This was discussed over at Neven's (starting here).  See also Arctic Sea Ice Hockey Stick: Melt Unprecedented in Last 1,450 years, where you will find this graphic (extent being an approximation of relative volumes over time):

    Click to enlarge

  2. Thanks for the link. From the discussion at Nevens its clear that Ms Slingos comments seem to be odds at what other scientists are saying. But I should imagine that her comments will be used by 'skeptics' to justify their exclusion of ice volume measurements and, in this case, they can point to a credible source to back up their argument.
  3. "Arctic sea ice loss is three times greater than Antarctic sea ice gain."
    That should be "three times as much as". It's different for the same reason that 50% more is different from 50% as much.
  4. Normal 0 false false false false EN-US X-NONE X-NONE

    The data presented above is outdated by a few years. The combined anomoly of NH and SH sea ice is trending upward since 2007. As electric rates have risen 40% over the last 7 years, justification has thinned more than the ice has.


    However, the Arctic ice volume 2014 peak is lower than the 2007 peak, but by a very small amount, far less than 1000 cubic km (PIOMAS). I'm not seeing the Arctic sea ice decrease on the order of 'three times as much as' in recent data. Things are different than in July 2012. This year has seen the remaining Arctic ice exceed seven other recent years just since April 22nd (Charctic), due to slow spring 2014 melt and the remaining Arctic ice is only 5.4% less than this time in 1994. As a comparison, 1994 was a very cold winter as I moved from S. Fla to Indiana at the start of that deadly winter. The temp at my apartment hit -44F without the wind chill on MLK day. I considered the possibility that the cold air over the great plains that day contracted the U.S. such as to have caused the Oakland earthquake that same day. As I recently have read about ocean volume thermal expansion due to surface temp increase, it might not have been so far fetched a thought.


    [PS] This moderator is struggling to decide whether you actually cant understand that cherrypicking and short trends are not science or whether you are trolling. You have been called on this before.

  5. Jetfuel @4, let me see...

    1)  Use of short time span for comparison?  Only eight years of a 30 plus year record used.  Check!

    2)  Use of previous record breaking year as start point for comparison?  2007 record year used.  Check!

    Well, your certainly playing from the denier play sheet for bad science.

    Trying to turn an April PIOMAS which is less than the trend value into evidence that the trend is reducing certainly shows gumption, but surely you must know that such unethical distortions of the facts will get called on this site:


    [PS] Jetfuel, please ackowledge that you understand Tom's point. If you dont understand, then more explanation is likely to be offered. If we get a "look, squirrel" instead, then your posts will be deleted.

  6. Response @4&5.

    The cherry-picked number,Δ(Arctic Sea Ice Volume maximum 2007 & 2014), described as "a very small amount, far less than 1000 cubic km (PIOMAS)" is 750 km3, which over a seven year period and in the units used in the graph @5 represents a trend of -1.07 (1000 km3/Decade). It isn't a very ripe cherry.

    The comparison presented @4, that of Arctic Sea Ice loss being allegedly not "on the order of 'three times as much as' in recent data," it is a comparison with Antarctic Sea Ice gain. Antarctic Sea Ice Volumes are not as well understood as their northern equivalents, but Holland et al (2014) suggest an Antarctic Sea Ice Volume trend of +0.3 (1000 km3/Decade) for 1992-2010. Ironically, that is about a third the size of the cherry-picked measure of ice loss in the Arctic.

  7. I do wonder if the attempt by jetfuel@4 to challenge the assertion made in this post (that Antarctic Sea Ice is growing at a much slower rate that Arctic Sea Ice is shrinking) should be batted away innto the long grass simply because of the incompetence of jetfuel to state his case.

    It is true that over the satellite record (1979 - to date), the decline in Arctic Sea Ice Area & Extent is roughly three times larger than the increase in Antarctic Se Ice Area & Extent. It is also true that both the Arctic decline and the Antarctic increase - both these trends have shown signs of acceleration over recent years, yet generally the three-to-one ratio remains. And it is true that the acceleration in trends is accompanied by greater variability but this has not resulted in net global Sea Ice area & extent anomalies reaching any unprecedented values* when examined as daily, monthly or quarterly averages, *unprecedented taken as values over the last decade, there being variability evident with such periodicity.
    However, recent Net Global Sea Ice area & extent do start to show unprecedented values* when Annual Averages are examined. This results mainly from the Antarctic anomaly showing a rising trend over the last two years. While this remains presently a short-term phenomenon, the mechanisms behind the growth of Antarctic Sea Ice area & extent are known to be the product of Antarctic regions with increasing sea ice cover and other Antarctic regions with decreasing sea ice cover. The net Antarctic anomaly is the result of two far larger values that presently come close to cancelling each other out. Such a cancellation cannot be relied on. One of the mechanisms (for increase or decrease) could easily come to dominate the anomaly in future decades, as may have been the case prior to the satellite era. Indeed, Fan et al (2014) argue quite convincingly that the start of the satellite data (1979) likely coincides with a shift from significant Antarctic summer (DJF) ice loss over the period 1950-78.
    Thus, while the comments by jetfuel are based on cherry-picking nonsense, and while the Net Global Sea Ice area & extent has been in decline over the satellite era (1979 - to date), predicting a continuation of that decline is potentially foolhardy as future trends, in particular Antarctic Sea Ice cover, remain uncertain.

  8. Is the scale on the Antarctic Sea Ice Extent graph in Figure 2 correct? I thought that Antarctic sea ice was up around the 20 million sq km mark. Thanks.

  9. Rett,

    The data in figure 2 is a 12 month average, not the maximun.  The Antarctic sea ice maximun (this year) was just over20 million km2.  Sea ice was only that high for about one week.  Sea ice has dropped to about 18 million km2.  The yearly average is lower than the maximum is.  The graph is also from last year so it does not include the most recent data.

    The yearly average is more informative than the maximum because it tells us about what is happeing the entire year.  A graph of all the data can be found here (the graph is area not extent so the maximun this year is 17 million km2.  The graph of the Antarctic is about half way down the page.)

  10. I got into an argument recently with a denier who is convinced the gain of seasonal Antarctic sea ice compensates for the loss of Arctic sea ice, because the increased albedo in the south substitutes for the loss of albedo in the north. I worked up a graphic to show why that doesn't work.

    Below is a picture of the Earth in northern hemisphere summer. This is the time that the Arctic ocean under the collapsing northern sea ice is absorbing the most heat from the sun. This is also the time of the greatest extent of Antarctic sea ice, since it is winter in the southern hemisphere. This is the time of year when deniers claim the minor increase in seasonal Antarctic sea ice somehow compensates for the loss of permanent northern sea ice.

    The red streak at the top of the picture shows the amount of sunlight falling on the vanishing northern ice cap. The thin red line at the bottom of the picture shows the amount of sunlight falling on the “increased” southern hemisphere sea ice. Both are approximations. In the north, I enclose the entire ice cap, not just the parts that have vanished, because in a very few years the Arctic will be virtually ice-free in the summer. Likewise, I made the southern line about three times thicker than it should be, to allow for three times as much Antarctic seasonal sea ice gain than we’ve seen so far, so that deniers don't think I'm ignoring the possibility of more growth there.

    As you can see, the two red patches are not anywhere near the same size. The loss of Arctic sea ice cannot be compensated for by a gain in Antarctic winter sea ice, unless Antarctic winter sea ice begins to reach to Madagascar and to southern Australia.

    This graphic is only approximate. It may be more useful (and more complete) to do a series of more carfully-made graphics, starting with polar views that show both the average and the current extent of Arctic summer and Antarctic winter sea ice, and then probably a picture showing where the sun rays fall in September when the Arctic is at its minimum and the Antarctic is at its maximum. Probably also, the final graphic should be from the sun's point of view, showing the vast areas of now-open ocean lit by the sun in the north, and the thin sliver of arc where the Antarctic "increase" is located.

    If this does seem to be a useful approach, feel free to either adapt this graphic, or to request the series.

    All this ignores, of course, the fact that whatever happens near the South Pole can't possibly undo the changes to northern hemisphere climate (wind and ocean currents, loss of habitat, etc.) that the loss of Actic ice causes.

    Summer Solstice

Post a Comment

Political, off-topic or ad hominem comments will be deleted. Comments Policy...

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

Link to this page

The Consensus Project Website



(free to republish)



The Scientific Guide to
Global Warming Skepticism

Smartphone Apps


© Copyright 2015 John Cook
Home | Links | Translations | About Us | Contact Us