Why Scientists Should Question Everything: A Simple Example

"The important thing is not to stop questioning."

-Albert Einstein

A curious thing happened yesterday (10 November 2011): One of the first Tweets* I saw in the morning was one with a picture of Arctic sea ice trends from the University of Bremen's AMSR2 Sea Ice Maps page. We know that sea ice has been growing recently in the Arctic, and at quite a high rate, but this site seemed to show a sudden reversal of ice accumulation. This is the chart that appeared yesterday on the UB page** (note: I actually downloaded this chart myself and added the blue ellipse for reference):

Needless to say, this seemed strange to me, so I immediately went to the Northern Hemisphere Sea Ice Extent page of the Danish Meteorological Institute where ice accumulation appeared to remain on track:

The University of Bremen's mapping shows sea ice for both the Arctic and Antarctic, and looking at both you could see the downward tail on both yesterday:

As someone who has worked with time series data and graphing them, I immediately suspected some sort of systematic error in the data, though I know very little about their process other than the few details on the page. At any rate, today (11 November 2015) I found this chart of arctic sea ice extent:

The downward tail was gone this morning. Although not shown, it was gone for Antarctic sea ice extent as well.

I could find no information on the UB page for this issue, though they do apparently provide a tracking page for irregularities.

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* To preserve confidentiality, I am not publishing the identity of the Tweeter.
** This is also not the same chart as on the Tweet. That chart had the last seven years plotted, whereas the one I'm using has the last six years plus 1979. The UB page displays both. The difference here is irrelevant because both series of charts had the same problem.