More on northern sea ice

A popular internet meme runs something like “melt was similar back in…”, usually referring to some arbitrary period in the 1920s or 30s. Well, unsurprisingly, there really are quite good records from then, and, unsurprisingly, they show nothing remotely like current ice conditions:


The animation is drawn from the Danish Meteorological Institute’s sea ice maps for August in each year from 1920 to 1939.  The red marks show actual records of ice conditions and the white area is the inferred ice extent. The last image is the US National Snow and Ice Data Center’s satellite-derived sea ice concentration image for August 2012.

There’s also the historical sea ice extent compilation by Walsh and Chapman at the US National Center for Atmospheric Research / University of Illinois (as plotted at Cryosphere Today):

History of seasonal sea ice 1900-2010, NOAA


Again, ever considered the possibility you’ve been lied to?



Also see:

7 comments to More on northern sea ice

  • Susan Anderson


  • Kevin O'Neill

    Great job. Steven Goddard will not be amused 🙂

  • Nicely done. Permission to repost at ?

    • Gerg

      Sorry, not sure why that got spam-trapped. Sure, please use as you see fit … must change that default copyright tag.

      (I don’t own the raw images of course, but I’m not expecting the DMI to attempt to challenge fair use. The actual image scans and the last image itself are US government publications, so not copyrighted.)

  • Dan H.

    Nice work, but I have two questions. First, do they have anything between 1939 and the present. Second, do you know why the sea ice maps do not match up with the Walsh and Chapman compilation?

    • Gerg

      I’ll play just once Dan in the spirit of goodwill. Answers are in the source links provided. The Danes were somewhat preoccupied 1940-45; they resumed publication in 1946. Walsh and Chapman give a source for every grid square for every month of their 142 year sea ice concentration compilation. They use 8 different sources, only one of which is DMI. The sources for their seasonal sea ice extent time series (as plotted; data here, down the bottom) are less obvious, but Kelly, 1979 appears to dominate. Maybe email Bill Chapman and ask him.