ARCTIC SEA ICE –Brief thoughts on DMI “shoreline masking” problem–

Over the past couple years the Danes have tried to make their measurements of sea-ice more precise, which is admirable. I have always tended to give them the benefit of the doubt, in issues regarding sea-ice, because sea-ice is serious stuff to them, as they have to deal with it. Their fishermen deal with it and are an important part of their economy, and they have a close association with Greenland, which is awash with sea-ice. But their simple attempt to be more precise has made an amazing mess.

What was involved was a so-called “mask” which runs along shorelines, and in effect disqualifies shorelines from sea-ice measurements. There are many reasons for doing this, two of which I saw when living on the coast of Maine during bitter cold winters.

1.) Big tides can make a mudflat “open water” one mild morning, but “ice-covered” the next.

2.) Big winds can shove the ice to the coast in the morning and then pull the ice away when winds shift in the afternoon.

It would take a whole staff of observers simply to measure the ups and downs along coasts. It is far, far simpler (and cheaper) to skip the bother by skipping the coasts. Skipping-the-bother was called a “mask”, and ran along all the convoluted ins and outs of the arctic shores.

The change was to make the “mask” thinner. This immediately added ice to the amount counted, because sea-ice that wasn’t counted before was now counted.

One wonders how much ice such a small change in the “mask” could be? Surely it would be a tiny amount, would it not? I myself don’t know, but have heard that 1.4 million sq km of ice was added to the amount counted, which is not a tiny amount.

Adding so much ice to the total made the old DMI “30%” graph, which wasn’t adjusted, read too high, even as the new “15%” graph was adjusted, and read lower. This disagreement put DMI in an awkward position, where their own graphs disagreed hugely, and their response was to simply discontinue the old “30%” graphs. They simply could not spend the time to fix the problem in the old graphs.

They did have to spend the time to fix the problem with the new gtaphs, because you cannot have the sea-ice “extent” jump by 1.4 million and not expect an uproar. However to simply subtract 1.4 million is too simple an answer. Why not? I made an attempt to explain why things are not so simple, on another site, as follows:

“1.4 Million sq km is a nice figure for winter sea-ice, but even in the winter there are problems with it, because when the weather patterns are meridienal even in the winter the ice may not be snug with the shore, as polynyas form even when temperatures are far below zero in places like the top of Baffin Bay or the coasts of Siberia, when off-shore winds roar.

If there is no ice at all along the shore, it doesn’t matter if you mask more or mask less; zero ice is zero ice. Any program that assumes you need to add ice along that shore, due to less masking, is an adjustment that will need adjusting.

Now May has past, and we are no longer talking about winter sea-ice. We are talking about June sea-ice, and there will be a lot more open water along the shores. It matters less and less whether you halve or double the masking along the shores, because there is no ice in the area you are masking.

In the winter such a potential glitch is minor, as polynyas swiftly skim over with thin layers of ice. In the spring polynyas stop freezing over, and appear downwind of every shoreline. (For example, downwind of Wrangle Island.)

I very much doubt that the fellows at DMI go on blithely adding 1.4 million sq km of ice as a “masking adjustment” right through the summer. After all, they aren’t nincompoops. What I mean to suggest is that the jobs becomes more difficult, due to the need for the adjusted adjustment.”

This is only a guess on my part, but I wonder if such an “adjusted adjustment” may explain why the amount of sea-ice abruptly grew in these DMI maps, between May 24 and May 25. (Hat tip to Svend Ferdinandsen.) (May 24 is to the left, and May 25 to the right.)

May 24 satcon.arc.d-05 May 25 satcon.arc.d-04

(The best way to compare the above maps is to open them in new tabs, and then switch back and forth between them. You will notice an increase in ice that weather conditions can’t explain.)

Often I notice maps show sudden appearances or disappearances of ice, such as the one I point out above. My assumption always is that the fellows behind the scenes are dealing with some difficult problem, and have had to “tweak” the way a program handles data.

It would be best if we could deal with such problems like super-engineers, beforehand, and not later, when they explode in our face. However even super-engineers know of something called “Murphey’s Law”,  (also expressed in a famous Scottish poem as (roughly) “The best laid plans of mice and men often go astray.”) All too often we have to deal with problems we never imagined would occur.

Who would have guessed simply reducing the “mask” along the arctic shoreline could cause such problems? (Likely there was some old Danish grouch warning the young idealists, but he was deemed a “wet blanket”, a “wrench in the works” , a “fossil”, and about fifteen other disparaging things I can think of, and then “fools rushed in, where wise men fear to go”. To which I reply, “Respect your elders” [especially me.])

In any case, it probably seemed a good thing initially to reduce the “mask” along the arctic shoreline by 50%. Is it not good to be more precise? Now the person or persons are facing “unintended consequences”, because people are noticing odd illogical happenings occurring in maps, and are being very rude and quoting Shakespeare and saying “something stinks in Denmark.”  This is unsympathetic and unfair.

Often, when you simply ask, or simply point out ice has vanished and/or appeared, and do so to the scientists involved with a polite email, you will receive a polite and sometimes quite lengthy and detailed explanation.

We should not stop asking questions. We especially shouldn’t automatically deride either the questioned (in this case DMI) or the questioner (in this case me.)

These things happen.


Hat-tip to the Blogger “Craig T” who produced this map over at . It does an excellent job of showing how reducing the “mask”(deep blue along the shores)  creates the impression there is more ice. (Green is ice that exists this year that didn’t exist on the same date last year.)