Friday, October 26, 2012

NASA's latest polar sea ice images, north and south

Sea ice September 2012. Arctic summer, Antarctic winter. Yellow outlines indicate previous averages.
Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio and NASA Earth Observatory/ Jesse Allen
NASA doesn't only explore the solar system, it has an Earth monitoring programme and employs climate scientists. A few days ago they issued two striking images of Arctic and Antarctic sea ice.  Enlarged images available on NASA Earth page.

September 2012 witnessed two opposite records.

Left: the Arctic Ocean's ice cap experienced an all-time summertime low for the satellite era.

Right: Two weeks later, Antarctic sea ice reached a record winter maximum. (In extent, though not thickness.) 

The yellow outlines are for comparison, indicating recent averages. In the Arctic image, average sea ice minimum extent from 1979 to 2010. In the Antarctic image, median sea ice extent in September from 1979 to 2000.

Dr James E. Hansen
NASA says that sea ice in the Arctic has melted at a much faster rate than it has expanded in the Southern Ocean, as can be seen in this image by comparing the 2012 sea ice levels with the yellow outline.

Dr Claire Parkinson, a climate scientist with NASA's Goddard Space Flight Center is quoted saying : "There's been an overall increase in the sea ice cover in the Antarctic, which is the opposite of what is happening in the Arctic. However, this growth rate is not nearly as large as the decrease in the Arctic.”

Lest we take the Antarctic image as a hopeful sign, she cautions that
some areas of the Southern Ocean cooling and producing more sea ice does not disprove a warming climate.

"Climate does not change uniformly: The Earth is very large and the expectation definitely would be that there would be different changes in different regions of the world.  That's true even if overall the system is warming.”

Another recent NASA study showed that Antarctic sea ice slightly thinned from 2003 to 2008, but increases in the extent of the ice balanced the loss in thickness and led to an overall volume gain.

NASA's Goddard Institute for Space Studies is led by James Hansen, a noted climatologist who has become a hate figure for oil companies due to his warnings about human-induced climate change.  


  1. I've been trying to figure out in my head if there is any siginficance to the fact that the Arctic figure is an average, but the Antarctic figure is a median. I can't quite work out of that matters. Does it?

  2. I doubt it. For the purpose of comparing the polar regions it would have been preferable to use the same sort of average for each, but I'm sure in this instance it wouldn't affect the conclusion, namely that the Arctic and Antarctic are behaving differently.

    By the way technically it's sloppy wording. They ought to have said the Arctic image represents *mean* sea ice minimum. The mean and the median are two different ways of calculating averages. Here’s an excellent maths website on averages:

    1. Yes, it's quite confusing sometimes because of the fact that 'average' is frequently, lazily, used to imply that the speaker/writer is on about the 'mean average'. The descriptions of each on that website are very clrear.  Thanks.