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Oct 20 2010

Increasing southern sea ice

This post was written for Skeptical Science as a “basic rebuttal” to the argument “Southern sea ice is increasing”.

Sea ice around Antarctica has increased over the few decades that satellites have been measuring sea ice extent. First of all, it’s worth remembering that sea ice is not to be confused with land ice. This distinction might seem obvious, but the two are often confused in media reports. Sea ice is frozen seawater floating on the surface, whereas land ice is a layer of snow that has accumulated over time on a landmass. Antarctica is losing land ice at an accelerating rate.

However, it is clear that the extent of sea ice around the coast of the continent is growing. Why? The first explanation which comes to mind is that the Southern Ocean must be cooling. But on the contrary, the Southern Ocean has warmed by around 0.5°C in the three decades since satellites began measuring sea ice trends.

The true reasons for the increasing ice are a complex set of factors. One factor is an increase in precipitation over the Southern Ocean, which means more snowfall. However, this trend is expected to reverse in coming decades as the Antarctic continues to warm.

Finally, southern sea ice is not particularly important to the climate. Unlike land ice, sea ice doesn’t affect sea levels because it’s already displacing water. And unlike the situation in the Arctic, where disappearing sea ice is making the Arctic Ocean less reflective and amplifying Arctic warming, a decline in southern sea ice would not warm the Antarctic climate. For as long as climatologists have studied it, the Southern Ocean has been almost ice-free in summer, the time of year when it would receive enough heat from the Sun to have a large effect. The issue of southern sea ice is really just a distraction which diverts our attention from the more important issue of sea ice melt in the Arctic.

In conclusion, the increase of southern sea ice does not contradict global warming. The Southern Ocean is in fact warming, the increase of sea ice is due to a variety of factors, and sea ice is not as important to the Antarctic climate as it is to the Arctic.

1 comment

  1. colinc

    James, I just found your site via a comment you wrote to a recent Joe Romm article. I find myself surprised that a “teenager” is capable of writing so lucidly. It’s a damn shame that older and [allegedly] “more educated” people can’t seem to manage that!

    That notwithstanding, you say above, “Sea ice is frozen seawater floating on the surface.” It is not! If you really look at the dynamics of ice formation on a body of saltwater you’ll find that as the water freezes it causes the salt molecules to precipitate. In other words, the salt gets “squeezed out.” Therefore, it is more appropriate to say that “sea-ice” is frozen _fresh_ water floating _in_ the seawater. Even a one-inch layer of “fresh” ice can be retrieved from any ocean you like, melted in a container and consumed just like water from your faucet with no ill effects. You’ll never taste the salt.

    I did read the link and “most” of the comments in the Skeptical Science blurb regarding “a complex set of factors.” While it is not “incorrect” it still misses what I consider the merely freaking obvious. When “ice-shelves” or “icebergs” or even “land ice” melts, it is _fresh_ water which floats on seawater because of the difference in density (or, if you prefer, specific gravity). Furthermore, fresh water, floating on top of seawater freezes more readily and quickly than seawater due to the fact there is much less salt in it. If you take into account the dramatic findings of the autonomous-sub survey under the Antarctic ice-shelves in February of 2009 and the observed warming of the seawater, it is, again, merely obvious that there is more _fresh_ water floating on the southern seas than ever before in the history of our species. Therefore, increasing ice on the ocean around Antarctica “should be” raising even greater alarm than the rapid deterioration of the Arctic ice-cap. The fact that it is not (raising the alarm-level) is only evidence of extreme ignorance, incompetence… or bald-faced lies.

    In an effort to ensure I’m communicating “clearly,” yes, the increased precipitation is certainly a contributing factor. However, I am sure that the increased “sea-ice” around Antarctica is more attributable to the accelerating pace of ice-melt “from below!” If/when you get around to “studying” thermodynamics, you’ll find that water conducts heat much more effectively and much more rapidly than air. About 20-times quicker if I’m remembering correctly. To demonstrate, stand in an air-conditioned room (to eliminate any “wind-chill” factor) that’s at about 15 C with no clothes on but your shorts. Time how long it takes for you to become “uncomfortably chilled.” After “warming up,” run yourself a bath (“room temperature” is irrelevant) in which the water is about 15 C and, dressing the same, get in and time that interval to discomfort. Let me know if you can stand being in the water for more than a small fraction of the time in the air. Feel free to contact me, for any reason, if you wish.

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