Melt season

Two summers: On the left, 1980; on the right, 2012.
(The picture is of the Arctic Ocean (with Iceland at the bottom and Alaska towards the top). It is about 3000 miles from side to side).

We tend to use ‘global warming’ and ‘climate change’ almost as synonyms, but that’s not quite right: the climate is changing, and one of the ways we see that change is as an increase in global mean temperature. We like global temperature as a measure partly because it is relatively well observed and understood (thanks, in a small part, to our contributions), but climate change is also showing itself in other ways, some of them more dramatic.

Every year in the Arctic, the sea-ice starts to melt in March and continues to retreat through the summer, reaching its minimum extent in September. Since 1979 we’ve been able to watch the change by satellite, and even over the 30-odd years of satellite observations we’ve seen some big changes, particularly in the summer ice coverage:

This is one reason why we are now concentrating on polar data. Arctic sea-ice is harder than global temperature – to measure, to understand, and to predict. So more observations are particularly valuable. And because changes in ice cover can be so large, we can make useful comparisons to modern records even with a limited set of ship observations: in 2012 the Northwest passage was clear of ice – it’s certain that William Parry, John Franklin, Roald Amundsen, and even our own Thetis, met very different conditions.

7 responses to “Melt season”

  1. Deb says :

    A picture is truly worth a thousand words- thank you for this. I think it would be great if you showed the scale of this picture- I know, its the north pole, it should be intuitively obvious that its very very big, but if viewers could be reminded that we are looking at thousands of miles of sea ice, or not, it might be helpful.

    • Philip says :

      Thanks for the suggestion – maybe it is a slightly unusual view of the world. I’ve added a comment to the post.

      If you look at a globe from directly above, with the UK on the side facing you, you will see the same image. It is 45 degrees of latitude (about 3000 miles) from side to side.

      There is a lot of sea ice in the winter – 16.13 million square killometers (msq) in March 1980, reducing to 15.24 msq in March 2012 The reduction is bigger in the autumn: 7.85 msq in September 1980 to 3.63 msq in September 2012 (data from NSIDC).

  2. derek koonce says :

    I would like to see the anartic side of things as well. Looking at one side of the Earth is limiting the field of view.

  3. Margaret Kosmala says :

    Cool video, Philip! What did you use to make it?

    • Philip says :

      I made it with R, mostly, using several packages from CRAN.

      The sea-ice data I took from ERA-Interim, using the chron and ncdf4 packages.
      The map background comes from the mapdata package.
      Those provide polygons of both land and sea-ice, which I plot using grid graphics.

      Those tools let me make a plot which provides one frame of the video. Then it’s just a matter of making 858 such plots – one for each 6-hour period between March and September. To turn the 858 plots into a video I used ffmpeg.

      All that software is open source – it’s amazing how many giants are willing to lend their shoulders.

      I am still in the silent movie era though – any suggestions for adding sound?

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