CAPIE stands for Cryospheretoday Area Per IJIS Extent (another more scientific term is 'compactness'), the index which we collectively created last year and that is regularly mentioned in the weekly SIE updates. I'll quote from last year's blog post that saw the birth of CAPIE, called Area vs Extent, to explain what CAPIE means and what it is useful for:
It tells us something about how much the ice pack is spread out. When the pack gets compacted area and extent will come closer together. But in the melting season the gap gets greater. This is because ice is melting, gets spread out and melt ponds start to form.
If you look at the ice pack as a whole, the holes that form away from the edges are not counted as sea ice area, but they do get counted as sea ice extent. That's because for extent every grid cell that contains more than 15% ice is counted as 100% ice. In consequence area will always be lower than extent.
Because of the difference between the ways area and extent are calculated, we can divide the first by the second and this gives us a percentage that, especially in comparison to other years, tells us something about how much the ice pack is compacted or spreading out. If the ice spreads out, there will be more holes, area will drop faster than extent, and thus the area/extent ratio will drop. If the ice gets compacted by winds, holes will disappear, the difference between area and extent becomes smaller and the percentage goes up.
Well, due to a huge drop in CT sea ice area CAPIE has hit an all-time low: 57.39%. As can clearly be seen on our CAPIE graph:
- Aug. 16th 2005: 69.53%
- Sept. 26th 2006: 67.69%
- Aug. 19th 2007: 60.01%
- Aug. 13th 2008: 59.57%
- Aug. 16th 2009: 63.91%
- Sept. 3rd 2010: 60.28%
- Aug. 12th 2011: 57.39%
But I don't think this is just the ice pack spreading a lot. I think that in a significant part of the Arctic - the Pacific side to be exact (the Beaufort, Chukchi and East Siberian Seas) - the ice is, to quote Professor Peter Wadhams from this BBC interview a few years back, "just melt[ing] away quite suddenly". Or to link back to the title of the last SIE update: flash melting. And it's showing up in area numbers first.