A Tale Of Two Indices
By Paul Homewood
I mentioned the other day that claims of “record low” Arctic ice foundered on the fact that the difference involved was so small to have been well within any margin of error.
Ron Clutz updates the situation, comparing MASIE with the Sea Ice Index, used for public consumption by NSIDC:
Sorry to be serious on April 1. I am not a fan of ice charts restricted to one month, for reasons illustrated in the post Ice House of Mirrors (some humor there in honor of this day.) But March monthly average sets the baseline for the year’s melt season, and so there is considerable attention and significance attached to the month just concluded.
Here is a chart showing March 2016 compared to the previous ten Marches according to two different indices of Sea Ice Extent: MASIE (Multisensor Analyzed Sea Ice Extent) produced by the National Ice Center and SII (Sea Ice Index) produced by NOAA (both accessed at NSIDC).
It is evident that the March annual maximum is trending slightly upward in MASIE and slightly downward in SII. Note that the indices were quite similar the first five years. Then since 2010, SII has declined quite strongly.
The differences between the two remind us that measuring ice extent is not an exact science.
Read Ron’s full analysis here.