Antarctic Sea Ice Index (part 2)
A trip down under: first order differential of mean sea ice extent, ice shelves, mélange & ocean swell
In part 1 of this series we noted a steady build of Antarctic sea ice up to a maximum annual mean of 12.78 million square kilometres attained during 2014, after which the ice extent dramatically collapsed to 11.20 million square kilometres within the space of two years. We might ask if Antarctic sea ice can melt that fast, being an equivalent melt rate of 0.79 million square kilometres per year, but the trouble is we don’t have the data down under to substantiate this.
If we pop up North and squint at the second slide in Arctic Sea Ice (part 4) we discover the fastest sustained melt rate attained was between 1992 and 2007 when the Arctic lost 1.62 million square kilometres within the space of 15 years, thus providing a maximal melt rate of 0.11 million square kilometres per year in a region famed for dramatic ice loss. We are thus asked to believe that the rather more frozen Antarctic managed to beat the warmer Arctic by a factor of x7.2. I think not.
Clearly something dramatic happened down under between 2015 and 2016 that doesn’t feel like a ‘melt’ as such so I decided to do a bit of sleuthing. Here’s a visual representation of the situation, being the first order differential (i.e. year-on-year change) of mean annual Antarctic sea ice extent that was portrayed in the first slide of part 1. These excursions usefully indicate when something distinctly odd happens: