Sea ice gains in Antarctic do not cancel out losses in Arctic

13 02 2015

More on Climate Change from our resident climate scientist Mark Cochrane…….

Sea ice cover in the Arctic has now been clearly dropping for several decades now. This is why we have the recent rush for riches to drill the Arctic for oil. You can now sail a tanker across the top of Siberia to China in the summer and the window of time when the area is ice free is only expected to increase in coming years. Summers may be ice free before the decade is out.

Despite this phenomenal change in the planet’s ice cover (where do we tell kids Santa lives?), you will also hear that sea ice is increasing around Antarctica being mentioned as if it somehow made the Arctic losses unimportant. While it is true that winter gains in sea ice have been occurring in the Antarctic region, the causes are completely different and probably not comforting. The Arctic is a floating ice sheet surrounded by land. The Antarctic sea ice surrounds a continent of land covered in ice.

Why is this distinction important? The ice sheets covering Antarctica are melting, with the western Antarctic ice sheet now past the point of return. It will collapse into the sea and melt no matter what we do (link). Ice that melts off the continent pours fresh water into the oceans making the surface waters less dense than the existing sea water. Being less salty, it also freezes more easily. This, combined with changing wind patterns that move the ice out further from the continent, is likely causing the slight increase in sea ice cover (link). Though part of the increase might just be an artifact in how the satellite data are now being processed (link).

However, for those who are unconvinced by such arguments, we can simply compare the area of ice being lost in the Arctic to that being gained in the Antarctic to see just what the balance in total area of ice cover change has been. A recent paper (Parkinson 2014) shows these relative trends in the Arctic and Antarctic and their magnitudes for the 35 year period; 1979-2013.

All 12 months show negative trends over the 35-yr period, with the largest magnitude monthly trend being the September trend, at −68 200 ± 10 500 km2 yr−1 (−2.62% ± 0.40% decade−1), and the yearly average trend being −35 000 ± 5900 km2 yr−1 (−1.47% ± 0.25% decade−1).

That annual area of global sea ice cover being lost (35,000 km2) is larger than the state of Maryland  (or nearly Taiwan if you prefer). Clearly the increasing seasonal sea ice cover in Antarctica is not ‘canceling out’ the severe sea ice losses in the Arctic.