While the extent of Arctic sea ice was reaching an all time record low on Sept. 16, data from the National Snow and Ice Data Center showed that, Antarctic sea ice was at its highest level ever for that calendar day, and the fifth highest amount overall since 1979.
If that was the whole story, it may be tempting to dismiss the whole climate change issue as just a lot of noise — after all, if ice is growing at the south pole, maybe the ice melting at the north pole isn't such a big deal — but it's far from the whole story and there's even a plot twist or two.
To start, it's winter in the southern hemisphere. Therefore, just as the extent of Arctic sea ice steadily grows when it's fall and winter in the northern hemisphere, so does the extent of Antarctic sea ice when it's fall and winter in the southern hemisphere. Also, just as the Arctic sea ice reached its lowest levels, the Antarctic sea ice will reach its highest levels at the same time.
The geography of the Arctic and Antarctic are quite different. With the Arctic being an ocean surrounded by land, the ice there is mainly affected by changes in air and sea surface temperatures. With the Antarctic being a land-mass surrounded by ocean, the ice there is mostly affected by winds and ocean currents. Some studies are indicating that climate change in the southern hemisphere has strengthened the westerly winds. And since winds have a general cooling effect, the strengthening of winds could have slowed the melting of Antarctic sea ice.
Another factor is the ozone hole.
"The ozone hole affects the circulation of the atmosphere down there," says climate scientist Mark Serreze, director of the NSIDC. "Because of the ozone hole, the stratosphere above Antarctica is quite cold. Ozone in the stratosphere absorbs UV light, and less absorption [by] ozone makes the stratosphere really cold. This cold air propagates down to the surface by influencing the atmospheric circulation in the Antarctic, and that keeps the sea ice extensive."
Also, even though all that UV light is making it through to the ground, it is having hardly any warming effect because the high albedo of the ice and snow reflects around 90 per cent of the sunlight back into space. Any warming that is happening due to that 10 per cent that's absorbed is being counterbalanced by the cold from the stratosphere.
Added to this is the effects of climate change increasing the amount of snowfall over the Southern Ocean around Antarctica, which contributed to the amount of sea ice by insulating the surface of the ocean.
The shear size of the Antarctic ice sheets made getting accurate wide-spread measurements difficult. Then, in 2002, the Gravity Recovery and Climate Experiment (GRACE) satellites were launched into orbit and began to take surveys of the ice. As the mission gathered data, it showed that Western Antarctica was losing ice mass and East Antarctica was in ice-mass balance — gaining mass in the interior but losing just as much mass around the edges.
And now for the twist: yes, the amount of sea ice around Antarctica is increasing. Yes, areas of land ice in the interior of East Antarctica are getting thicker. However, first, there is a difference between land ice and sea ice, and how they respond to environmental changes. Second, there are large areas all around these thickening areas in East Antarctica that are in the process of melting. Most of Western Antarctica is melting, and the overall net loss of ice as melt-water is actually increasing the amount of sea ice around the continent.
Ice Mass Change (NASA image):
Why is this?
As the cold fresh water from the melting ice runs off into the ocean, it lowers the salt content of the water immediately around the ice sheets. Lower salt-content water is lighter and freezes easier than the more salty water around it. The run-off stays at the ocean surface, where some of it freezes, adding to the total extent of sea ice in the area.
So, the increase in sea ice is due to a net loss of land ice. Since nearly all of the sea ice around Antarctica completely melts away in the summer — compared to the Arctic where, for now at least, some ice survives the summer months — there is an overall net loss of ice there. As it continues, we can expect to see a gain in sea levels for the rest of the world.