Guest Post by Willis Eschenbach
I do my best to maintain my sense of awe regarding the things I study. I’ve had the good fortune in my life to be a commercial fisherman on the Bering Sea, and to voyage and fish on the edges of the Arctic ice. To me, sea ice, whether fixed to the shore or free-floating, is an awesome sight. As the poet said almost two hundred years ago,
And now there came both mist and snow,
And it grew wondrous cold:
And ice, mast-high, came floating by,
As green as emerald.
And through the drifts the snowy clifts
Did send a dismal sheen:
Nor shapes of men nor beasts we ken—
The ice was all between.
As I sift through the layers of dusty numbers and I work to understand the intricacies of the weather, I strive to maintain that sense of wonder at the scope and scale and beauty of what I am studying … but I digress.
As the song has it, I often “go to the corner, and I end up in Spain”. This time, I started out to examine what happens to the upwelling radiation when the ocean freezes over. To do this, I planned to use the Reynolds_v2_ice_cover dataset from KNMI (NetCDF is available at the bottom of the page). My idea was to compare the ice coverage data to the CERES satellite radiation dataset.
But when I had downloaded the ice cover data, here’s what I found out about the ice cover:
Figure 1. Sea ice coverage (total of northern and southern sea ice) as a percentage of total ocean area. Top panel shows the raw data. Middle panel shows the average seasonal cycle. The bottom panel shows the residual, which is the raw data minus the seasonal component.
This shows a curious evolution over time. Over the first decade plus of this record, the ice coverage gradually decreased by about half of a percent. Then from 2004 to 2010, the coverage rapidly increased by a full percent, and has stayed there for the last five years.
Now, I knew that the global sea ice has lately been on the increase. But I was unaware that the change was either that fast or that large. It increased by about one part in eight, about 12%, in a short six years. Among other things, this should be a cautionary tale about the unreliability of short ice datasets like this one …
Anyhow, I plan to follow this up by comparing the ice data to the CERES data. I just wanted to highlight this frozen oddity.
Regards to all,
My Usual Request: If you disagree with me or anyone, please quote the exact words you disagree with. I can defend my own words. I cannot defend someone else’s interpretation of some unidentified words of mine.
My Other Request: If you think that e.g. I’m using the wrong method on the wrong dataset, please educate me and others by demonstrating the proper use of the right method on the right dataset. Simply claiming I’m wrong doesn’t advance the discussion.