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It's the sun
Climate's changed before
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
It hasn't warmed since 1998
Ice age predicted in the 70s
We're heading into an ice age
Antarctica is gaining ice
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Is Antarctica losing or gaining ice?

The skeptic argument...

"The amount of ice surrounding Antarctica is now at the highest level since satellites began to monitor it almost 30 years ago. It’s simply too cold for rain in Antarctica and it'll stay that way for a very long time. The bottom line is there is more ice than ever surrounding Antarctica." (Patrick Michaels).

What the science says...

While the interior of East Antarctica is gaining land ice, overall Antarctica is losing land ice at an accelerating rate. Antarctic sea ice is growing despite a strongly warming Southern Ocean.

It's important to distinguish between Antarctic land ice and sea ice which are two separate phenomena. Reporting on Antarctic ice often fail to recognise the difference between sea ice and land ice. To summarise the situation with Antarctic ice trends:

  • Antarctic land ice is decreasing at an accelerating rate
  • Antarctic sea ice is increasing despite the warming Southern Ocean

Antarctic Land Ice is decreasing

Measuring changes in Antarctic land ice mass has been a difficult process due to the ice sheet's massive size and complexity. However, since 2002 the Gravity Recovery and Climate Experiment (GRACE) satellites have been able to comprehensively survey the entire ice sheet. The satellites measure changes in gravity to determine mass variations of the entire Antarctic ice sheet. Initial observations found that that most of Antarctic mass loss comes from Western Antarctica (Velicogna 2007). Meanwhile, from 2002 to 2005, East Antarctica was in approximate mass balance. The ice gained in the interior is roughly balanced by the ice loss at the edges. This is illustrated in Figure 1 which contrasts the ice mass changes in West Antarctica (red) compared to East Antarctica (green):


Figure 1: Ice mass changes (solid lines with circles) and their best-fitting linear trends (dashed line) for the West Antarcica Ice Sheet (red) and East Antarcica Ice Sheet (green) for April 2002 to August 2005 (Velicogna 2007).

As more GRACE data came in, a clearer understanding of the Antarctic ice sheet emerges. Figure 2 shows the ice mass changes in Antarctica for the period April 2002 to February 2009 (Velicogna 2009) . The blue line/crosses show the unfiltered, monthly values. The red crosses have seasonal variability removed. The green line is the best fitting trend.


Figure 2: Ice mass changes for the Antarctic ice sheet from April 2002 to February 2009. Unfiltered data are blue crosses. Data filtered for the seasonal dependence are red crosses. The best-fitting quadratic trend is shown as the green line (Velicogna 2009).

With the longer time series, a statistically significant trend now emerges. Not only is Antarctica losing land ice, the ice loss is accelerating at a rate of 26 Gigatonnes/yr2. It turns out that since 2006, East Antarctica has no longer been in mass balance but is in fact, losing ice mass (Chen 2009). This is a surprising result as East Antarctica has been considered stable because the region is so cold. This indicates the East Antarctic ice sheet is more dynamic than previously thought. This is significant because East Antarctica contains much more ice than West Antarctica. East Antarctica contains enough ice to raise global sea levels by 50 to 60 metres while West Antarctica would contribute around 6 to 7 metres. The Antarctic ice sheet plays an important role in the total contribution to sea level. That contribution is continuously and rapidly growing.

Antarctic Sea Ice is increasing

Antarctic sea ice has shown long term growth since satellites began measurements in 1979. This is an observation that has been often cited by skeptics as proof against global warming. However, rarely is the question raised: why is Antarctic sea ice increasing? The implicit assumption is that if Antarctic sea ice is growing, it must be cooling around Antarctica. This is decidely not the case. In fact, the Southern Ocean has been warming faster than the rest of the world's oceans. Globally from 1955 to 1995, ocean have been warming at 0.1°C per decade. In contrast, the Southern Ocean has been warming at 0.17°C per decade. Not only is the Southern Ocean warming, it is warming faster than the global trend.


Figure 3: Surface air temperature over the ice-covered areas of the Southern Ocean (top). Sea ice extent, observed by satellite (bottom). (Zhang 2007)

If the Southern Ocean is warming, why is Antarctic sea ice increasing? There are several contributing factors. One is the drop in ozone levels over Antarctica. The hole in the ozone layer above the South Pole has caused cooling in the stratosphere (Gillet 2003). This strengthens the cyclonic winds that circle the Antarctic continent (Thompson 2002). The wind pushes sea ice around, creating areas of open water known as polynyas. More polynyas leads to increased sea ice production (Turner 2009).

Another contributor is changes in ocean circulation. The Southern Ocean consists of a layer of cold water near the surface and a layer of warmer water below. Water from the warmer layer rises up to the surface, melting sea ice. However, as air temperatures warm, the amount of rain and snowfall also increases. This freshens the surface waters. So now you have a surface layer that is less dense than the saltier, warmer water below. The layers become more stratified and mix less. Less heat is transported upwards from the deeper, warmer layer. Hence less sea ice is melted (Zhang 2007).

The bottom line is Antarctic sea ice is a complex and unique phenomenon. The simplistic interpretation that it must be cooling around Antarctica is decidedly not the case. Warming is happening - how it affects specific regions is complicated.

Printable Version  |  Link to this page

Further reading

Tamino compares and analyses the long term trends in sea ice data from the Northern and Southern Hemisphere in Sea Ice, North and South, Then and Now.

What's Holding Antarctic Sea Ice Back From Melting? by NASA reviews the studies into why Antarctic sea ice is increasing despite the warming Southern Ocean.

Comments 1 to 17:

  1. "Computer models have predicted that energetic particles hitting the top of the atmosphere in polar regions may change temperatures by stimulating the production of nitrous oxides (NOx)."

    "NOx destroys ozone in catalytic reaction cycles; and when you change ozone in the stratosphere, that... can then feed down to surface temperatures."

    From an article by BBC News "More doubt on cosmic climate link By Richard Black, Environment correspondent, BBC News website, Vienna" under the subhead Local change
    Response: I did see that article earlier today. The section on Antarctica is interesting although the phenomena they're describing seems to be regional and shows no long term trends - it's a localised, short term effect. However, what did get my attention was the section on cosmic rays as I've actually been preparing a post on that very topic - cloud cover during Forbush events. This new study covers the same material using different data so I contacted the author this morning hoping to get more info. More on this soon, I hope.
  2. John
    I noticed the ozone portion because it rang a bell fro what I had read previously in Mackeys paper.
  3. OK smarties. If Antarctica is overall losing ice, then how do you explain the data?

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.south.jpg

    The Arctic doesn't seem to be doing so bad anymore, also:

    http://arctic.atmos.uiuc.edu/cryosphere/IMAGES/current.area.jpg
    Response: It's somewhat discouraging that the first point I make is that people often fail to distinguish between sea ice and land ice. They are two separate phenomena. And yet you repeat the error. To clarify, Antarctica is losing land ice at an accelerating rate. Sea ice around Antarctica is increasing. The reasons for sea ice increasing in a warming Southern Ocean are complex and described in detail above.
  4. Second order skeptic at 22:45 PM on 24 June, 2008
    AnthonySG1: Your images are concerned with the ice _area_ . Ice _mass_ on the other hand is shrinking.
    http://www.jpl.nasa.gov/news/news.cfm?release=2008-010
  5. The misinformation on this site is astonishing.
    Antarctic ice is increasing.
    In addition to the cryosphere link provided Anthony,
    This is confirmed by NSIDC,
    http://nsidc.org/data/smmr_ssmi_ancillary/regions/total_antarctic.html
    by NCDC,
    http://www.ncdc.noaa.gov/oa/climate/research/2008/apr/global.html#seaice
    and by numerous scientific papers, including
    Cavalieri and Parkinson, J. Geophys. Res. 113, C07004 (2008),
    Comiso and Nishio, J. Geophys. Res. 113, CO2S07 (2008).

    You have managed to find one paper that finds a decrease - but that only covers a 3 year period! Obviously you cannot get a significant trend from 3 years data.
    Response: Please, people, pay attention! Sea ice is increasing. Land ice is decreasing. Read and reread the post above  until you realise they are two separate phenomena.
  6. "NASA Finds VAST Regions of West Antarctica Melted in Recent Past 05.15.07
    A team of NASA and university scientists has found clear evidence that EXTENSIVE areas of snow melted in west Antarctica in January 2005 in response to WARM TEMPERATURES. This was the first WIDESPREAD Antarctic melting ever detected with NASA's QuikScat satellite and the MOST SIGNIFICANT MELT observed using satellites during the past three decades. Combined, the affected regions encompassed an area as big as CALIFORNIA."

    My caps. - just look at the map and tell me the use of those words is justified. The ACTUAL area involved is a FRACTION of the ice sheets, even the IPCC reckon it would take over 1000yrs to melt if the worst of their predictions materialised.
  7. Increase in sea ice a bad thing

    http://www.slate.com/id/2192730/
    . . . No one's entirely sure what's causing the expansion of sea ice in Antarctica, but the likeliest explanation is a disturbing one. According to a 2005 NASA-funded study, warmer temperatures have caused greater snowfall around the continent's edges, where the open oceans provide plenty of raw material for precipitation. (Warmer air absorbs moisture more readily.) The weight of that excess snow pushes sheets of sea ice down into the water, causing more water to freeze.

    The incremental expansion of Antarctica's sea ice has coincided with some more troubling changes. Four of the continent's largest glaciers (whose fates are largely unrelated to that of sea ice) are retreating rapidly, and researchers blame increases in ocean temperature. The diminishment of such massive glaciers means that, despite the slow creep forward of the continent's sea ice, the total mass of all Antarctic ice—which includes inland ice—has experienced a marked decrease. And a continuation of that trend could lead to significant rises in global sea levels. Furthermore, snow is melting much farther inland than ever, as well as high up in the Transantarctic Mountains. . .
  8. PaulM,

    Chill, amigo (no pun intended).

    The article makes the distinction right off the bat between land ice and sea ice. Your two links discuss SEA ICE. We know there's been an increase in sea ice.

    In a place where the temperature is always well below freezing, "global warming" is not going to melt all the ice. That doesn't mean it isn't a problem elsewhere. Even if there were no net ice loss on earth, if we're losing ice in places we need it (such as mountain ranges that supply people with drinking water), and accumulate it in places that have no humans at all (Antarctica), that's an enormous problem.

    The persistence of climate change skeptics in using Antarctica to say "look, everything's ok", is really beyond absurd.
  9. Also remember as ice area increases so does the albedo, reducing SI locally. In addition land ice will decline as sea ice increases (WV has further to travel to reach central regions).
  10. Seriously? A graph from 2002?

    That's just silly. By moving the range a couple points in either direction you could get a trend going any way you want.

    Meanwhile, there's a 20-year graph that confirms Antarctica appears to be gaining mass:

    http://www.gsfc.nasa.gov/topstory/20020820southseaice.html
    Response: You're not the first (and I doubt you'll be the last) person to mistake sea ice trends for land ice trends. The article you link to is talking about sea ice, not land ice. Let me summate the situation in Antarctica: Sea ice is increasing. Land ice is decreasing.
  11. It should be noted that the observational period here is quite short, so one should be careful about firm conclusions.

    And, the precise extent may be somewhat lower than presented:

    Geodetic measurements of vertical crustal velocity in West Antarctica and the implications for ice mass balance

    Received 20 May 2009; accepted 28 August 2009; published 13 October 2009.

    Citation: Bevis, M., et al. (2009), Geodetic measurements of vertical crustal velocity in West Antarctica and the implications for ice mass balance, Geochem. Geophys. Geosyst., 10, Q10005, doi:10.1029/2009GC002642.

    "We present preliminary geodetic estimates for vertical bedrock velocity at twelve survey GPS stations in the West Antarctic GPS Network, an additional survey station in the northern Antarctic Peninsula, and eleven continuous GPS stations distributed across the continent. The spatial pattern of these velocities is not consistent with any postglacial rebound (PGR) model known to us. Four leading PGR models appear to be overpredicting uplift rates in the Transantarctic Mountains and West Antarctica and underpredicting them in the peninsula north of 65°. This discrepancy cannot be explained in terms of an elastic response to modern ice loss (except, perhaps, in part of the peninsula). Therefore, our initial geodetic results suggest that most GRACE ice mass rate estimates, which are critically dependent on a PGR correction, are systematically biased and are overpredicting ice loss for the continent as a whole."
  12. yes, agreed SNratio (re #11). However there are longer term measures of Antarctic ice mass loss from altimetry that are consistent with a nett mass loss in Antarctica (which is still pretty small in relation to the vast amounts of Antarctic ice) [*].

    We should also note that the corrections applied by Bevis et al. (2009) suggest that a bias in ice mass loss from GRACE measurements amounts to ~33 Gt/yr [**]. This is a significant, but small, proportion of the total Antarctic ice loss determined by GRACE (see figures in John Cook's summary above):

    [*] E. Rignot et al. (2008) Recent Antarctic ice mass loss from radar interferometry and regional climate modelling Nature Geoscience 1, 106 - 110 (2008)

    [**]Bevis et al. (2009) para [19]; page 9:

    We can estimate the potential magnitude of the ice mass biases by noting that if the average velocity prediction bias of ~5 mm/yr evident in Figure 5 is developed over ~2 × 10^6 km2, an area somewhat smaller than that of West Antarctica, this would cause an apparent but spurious ice loss of ~33 Gt yr-1, which is a significant fraction of all published ice mass rates derived from GRACE [Velicogna and Wahr, 2006; Chen et al., 2006; Ramillien et al., 2006; Sasgen et al., 2007a]. However, it is not possible to arrive at an accurate numerical estimate of the impact of our geodetic measurements on GRACE ice mass change solutions without finding a reliable means to interpolate between our point measurements of vertical crustal velocity.


    The authors (Bevis et al, 2009) also point out that GRACE should make reliable estimates of any further enhanced acceleration in ice mass loss (or sudden jumps in ice mass loss), since the post-glacial rebound (that has to be corrected for in mass change estimations) doesn't vary much on the interannual timescale.
  13. Sure chris, I did not mean to suggest that ice loss is _not_ happening, just to point out that we should be careful. The last thing the public debate needs, is accusations of "alarmism" with some degree of justification to them. Which could easily happen if this ice mass change, for instance, turns out to be a quasi-periodic phenomenon somewhat akin to the PDO.

    Another thing I am wondering about, is the net effect of the situation underlying the (rather slow) increase in sea ice. Albedo should be increasing a little bit, but what about the heat loss from sea? Could the extra warming of the sea and the increasing sea ice be two aspects of the same circulatory phenomenon? Maybe a stupid question, I'm not very much into this :-)
  14. No problem SNRatio. I think we're probably about on the same wavelength, and I agree that we should be careful not to over-interpret observations that might be "contaminated" by artefacts of the measurement, or confounded by factors that we haven't fully considered. I'm glad you found that paper.

    As for the slow increase in Antarctic sea ice over the past few decades, I don't really have much insight into that. It seems somewhat counter-intuitive, but if the evidence is sufficiently strong that sea ice has grown somewhat while ocean and air temperatures have increased, then we may as well accept for now what the science says in relation to deep Southern ocean stratification and the effects of the ozone hole...although I guess in this case that there's more t be learned on this little piece of natural phenomena.
  15. I think the point in #11 is that most attempts to estimate ice mass balance in the antarctic reply on IJ05 or ICE-5G to estimate PGR/GIA.

    Just to point out that similar work has been done for Eastern anarctic, here, with similar conclusions. Suggesting further error in the previous ice mass estimates including Velicogna 2009. This publication suggests the green line in Fig1 should maybe showing a gain over time.

    I'd highlight the second half of the Bevis quote in #12 which states that the 33Gt yr-1 is only a provisional figure (and covers only part of Western Antarctic)

    I'd be keen to see some full estimated that take into account the GPS data.
  16. As a physicist and as a windsurfer who relies on shoreline thermals for sail power, I wonder if any one has considered that rising ocean temperatures in the Southern Seas has increased the offshore flow of ice-cold air from the continental land mass. Might this not also contribute to the increased cooling of the ocean surface and to more sea ice?
  17. diogenes,
    in the Zhang 2009 paper cited, the wind field is taken from the NCEP-NCAR reanalisys. It's not shown nor I looked for it; but given that the surface temperature has increased (fig. 3 in this post) I don't think that there any significant large scale change in thermal winds at play. Locally and seasonally it might have an effect but i have no clue on this.

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