I had planned to do a post yesterday evening about how sea ice area and extent had returned to very near normal levels. But I was tired, so I saved off the graphs from the NANSEN arctic sea ice site.
This morning I was shocked to discover that overnight, huge amounts of sea ice simply disappeared. Fortunately I had saved the images and a copy of the webpage last night. Here is the before and after in a blink comparator:
There is no mention on the NANSEN website as to this change. So either it is an automation error or an undocumented adjustment. Either way, since this is for public consumption, NANSEN owes the public an explanation.
And there is more, see additional blink comparator graphs I’ve added below:
After examining the above, it appears the issue only manifests itself when comparisons to the 1979-2000 monthly average are made. The adjustment starting point appears to start around September 10th – at the summer minimum for both area and extent.
This could be a data processing error, though if so, it is so blatantly obvious to anyone who follows the NANSEN presentation that it immediately stands out. Many people commenting on this blog and others also saw the change without the benefit of my handy-dandy blinkj comparator above.
That fact that it occurs on a weekend could be viewed as suspicious due to fewer eyes on the website , or an indication that they have sloppy quality control there at NANSEN and this was published via automation with no human inspection prior to the update.
Steven Goddard writes via email:
The explanation (if one is offered) will be interesting to say the least.
I received this email from Stein Sandven at Nansen in response to my query:
The ice area calculation has been too high since about 22 October, causing too steep slope of the 2008 curve. We corrected for this yesterday and recalculated the ice area for 2008. The slope of the 2008 curve should now be correct and can be compared with 2007 and the previous mean monthly ice area.
For my opinion though it seems to be an incomplete answer, generating even more questions.