Thursday, October 4, 2012

Increasing Antarctic Sea Ice and Global Warming

I received a comment or two in response to my earlier post about the record Arctic sea ice melt, arguing that I should address the increasing sea ice around the Antarctic. There are climate skeptics who claim that the increase, which is small but exists (you'll have to scroll down to the bottom of the linked page) means that global warming is not happening, or at least concerns are greatly exaggerated. That is simply wrong. Justin Gillis, a writer for the New York  Times' Green blog, has recently written a post debunking the myth.

The bottom line is that the extent of what is happening in the Arctic dwarfs what is happening in the Antarctic. As Gillis puts it, "in percentage of ocean cover, the decline in Arctic winter ice is eight times as fast as the increase in Antarctic winter ice."

There's no question that the issues are complex. But the Arctic and the Antarctic are not directly comparable:

  • the Arctic is an ocean, confined and shallow, and surrounded by land. The Antarctic is a continent, land surround by deep ocean.
  • The poles are in different places. When it is summer in the Arctic, it is winter in the Antarctic, and vice versa. So simultaneous ice melt in one and ice growth in the other are expected.
  • The topography is different. As Gillis explains it, in contrast to the Arctic:
In Antarctica, when winter sets in and the sun drops low in the sky, sea ice can grow unimpeded over the huge ocean surface. But then, in contrast to the historical situation in the Arctic, about 80 percent of the Antarctic ice melts in the summer. So the Antarctic ice has always come and gone in an annual rhythm. Most of it does not hang around to reflect sunlight back to space at the time of year when Southern Hemisphere sunlight is strongest.
The blog Skeptical Science points out that the Southern Ocean is warming, even while Antarctic sea ice is increasing. Its conclusion:
In summary, 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.
Read these two columns for yourself for more detail and some useful graphics.

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