Saturday, August 2, 2014

Antarctic sea ice cover is increasing. Is Global Warming over?

sea ice Ross Sea. Photo © Bruce Luyendyk
Sea ice, Ross Sea, Antarctica, 1996. Photo © Bruce Luyendyk

Recent news items have drawn attention to Antarctic sea ice, the floating ice a meter or so thick that forms from freezing of the oceans surrounding Antarctica. Sea ice coverage is seasonal, more in the austral winter (June-September) and less in the summer (December-March), a difference of six-fold. A way to think of the scale is that the maximum extent of the sea ice about doubles the area of ice (land and sea) at the bottom of our planet. The story is that a glitch has been discovered in the estimate of the rate of change (change year over year) in the area of sea ice around Antarctica1,2.

Underlying the news of the glitch is the prior observation that the amount of sea ice has been increasing year over year. This is opposite the observation for the Arctic Ocean where famously, sea ice area has been shrinking year over year3.

First about the glitch; this is due to a difference in the methods used in computing Antarctic sea ice cover from satellite imagery. The method was changed in 1991.