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It's the sun
Climate's changed before
There is no consensus
It's cooling
Models are unreliable
Surface temp is unreliable
Ice age predicted in the 70s
We're heading into an ice age
It hasn't warmed since 1998
Antarctica is cooling/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 ever measured for this time of the year, since satellites first began to monitor it almost 30 years ago. All of the IPCC’s models of Antarctica in the twenty-first century forecast a gain in ice, as a warmer surrounding ocean evaporates more water, which subsequently falls in the form of snow when it hits the continent. Other studies, such as Peter Doran’s in Nature in 2003, show actual cooling in recent decades. It’s simply too cold for rain in Antarctica, and it’ll stay that way for a very long time. The bottom line is that there is more ice than ever surrounding Antarctica (source: Patrick Michaels).

What the science says...

Overall, Antarctic land ice is falling. Antarctic sea ice is growing despite a warming Southern Ocean.

It's important to distinguish between Antarctic land ice and sea ice which are two separate phenomenon.

Antarctic Land Ice

Measuring changes in Antarctic land ice mass has been a difficult process due to the ice sheet's size and complexity. However, over the last few years, the Gravity Recovery and Climate Experiment (GRACE) satellites have been able to comprehensively survey the entire ice sheet. Using measurements of time-variable gravity, Velicogna 2007 determined mass variations of the entire Antarctic ice sheet from 2002 to 2005. They found the overall mass of the ice sheet decreased significantly, at a rate of 152 ± 80 cubic kilometers of ice per year (equivalent to 0.4 ± 0.2 millimeters of global sea-level rise per year). Most of this mass loss came from the West Antarctic Ice Sheet. Figure 1 displays Antarctica's ice mass from 2002 to 2005 - the red crosses is their best estimate with the dotted line the linear trend.

Figure 1: GRACE monthly mass solutions for the Antarctic ice sheet for April 2002 to August 2005. Blue circles show results after removing the hydrology leakage. Red crosses show results after also removing the PGR signal. The latter represent our best estimates of mass variability. Also shown is the linear trend that best fits the red crosses.

Also illuminating is Figure 2 which contrasts the mass changes in West Antarctica (red) compared to East Antarctica (green):

Figure 2: Monthly ice mass changes and their best-fitting linear trends for WAIS (red) and EAIS (green) for April 2002 to August 2005.

Most of the Antarctic mass loss comes from Western Antarctica with a mass loss of 148 ± 21 km3/year. The mass loss from East Antarctica is 0 ± 56 km3/year. Because of its relatively large uncertainty, it's uncertain whether East Antarctica is in mass balance or not.

Why is Western Antarctica losing ice mass while East Antarctica is relatively steady. The hole in the ozone layer above the South Pole causes cooling in the stratosphere. This increases circular winds around the continent preventing warmer air from reaching east Antarctica and the Antarctic plateau. The flip side of this is the Antarctic Peninsula in Western Antarctica has "experienced some of the fastest warming on Earth, nearly 3°C over the last half-century".

Antarctic Sea Ice

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, in all the skeptic articles I've read, not one has raised the crucial question: why is Antarctic sea ice increasing?

Figure 1: annual mean sea ice extent, observed by satellite. Straight line is the trend line (Zhang 2007).

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 other oceans in the world. The average global ocean temperature trend has been 0.1°C per decade from 1955 to 1995. 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 2: Linear trend (1979–2004) of surface air temperature over the ice-covered areas of the Southern Ocean.

So this raises the big question: if the Southern Ocean is warming, why is Antarctic sea ice increasing? The paper Increasing Antarctic Sea Ice under Warming Atmospheric and Oceanic Conditions (Zhang 2007) attempts to answer this question.

The paper uses a coupled ocean/sea ice model to find the predominant reason that sea ice is increasing is due to a decrease in upward ocean heat transport. Eg - less heat is being carried up by ocean convection to melt sea ice. The reason for this is a complex chain of events.

When surface temperature increases, the upper ocean warms and ice growth decreases. This leads to a decrease in salt rejection from new ice. The salinity of the upper ocean falls. Lower salinity and warmer water results in lower water density in the upper ocean. With fresher, less dense upper water, there is now increased stratification of ocean layers which weakens convective overturning. Less ocean heat is transported upwards. This leads to a decrease in ice melting from ocean heat. Hence we observe an increase in net ice production - sea ice increases.

While all that is a bit of a mouthful, it's actually a simplification of the process as there are various feedbacks along the process. Warming air increases upper ocean temperature which affects air temperature through air-sea interactions. Warming temperature leads to increased precipitation which increases sea ice growth. More sea ice means less atmospheric heat can penetrate waters.

The bottom line is the answer to Antarctic sea ice isn't simple - the Southern Ocean is a complex system with a number of factors likely contributing. One factor certainly isn't a contributor - the simplistic explanation that it must be cooling around Antarctica is not the case. Warming is happening - how it affects specific areas is complicated.

Printable Version

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.

Comments 1 to 12:

  1. I suppose that the volcanic activity that they discovered recently has nothing to do with this?
  2. Wondering Aloud at 01:36 AM on 1 April, 2008
    Another one of those issues the more you investigate the less convincing it becomes.
  3. "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. ]
  4. John
    I noticed the ozone portion because it rang a bell fro what I had read previously in Mackeys paper.
  5. OK smarties. If Antarctica is overall losing ice, then how do you explain the data?

    The Arctic doesn't seem to be doing so bad anymore, also:
    [ Response: Funny you should ask, the last few weeks, I've been preparing a series of posts on Antarctica and the Arctic. First one next week. Stay tuned... ]
  6. 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.
  7. The misinformation on this site is astonishing.
    Antarctic ice is increasing.
    In addition to the cryosphere link provided Anthony,
    This is confirmed by NSIDC,
    by NCDC,
    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.
  8. "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.
  9. Increase in sea ice a bad thing
    . . . 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. . .
  10. 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.
  11. I'm very sorry, but on that one the antarctic land ice graphs are showing data from 2002 to 2005.

    This is unfortunately a way too little period of time to conclude anything.

    Furthermore, the scientific centers installed there have monitored the climate in Antarctica for now about 50 years, and their data shows a relative stability (little cooling?) over that period.

    Why are you not showing these results here? Trying to occlude results that are disturbing and don't confirm what you are trying to defend?...

  12. 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).

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