The post a few days ago on the Talkshop Could Instrumentation Drift Account for Arctic Sea Ice Decline? has led to a little discussion but also pushed me to take a brief look at sea ice, a subject where I spent some time, although before I started posting here. My loss of interest, was partly having found out as much as I was likely to and partly the parlous state of the data providers, a mess which continues. On top of that there aren’t many people interesting in the information side, is mostly armchair politics.
What I am now showing is all based on dataset d02135, monthly.
Extent and area follow each other quite closely, extent is used.
First for fun here is a plot as loved by NSIDC etc., one point per year by month, except I have put it all in one.
Nothing surprising. Might be useful for someone.
Now we come to the fun
I’d like to swear, resisted, what is going on? I know what is coming next. Waiting to see how things pan out there has been some kind of modal switch to much larger swings.
Opinion: In other work not shown here the drop in northern ice seems to fit with a rise is solar UV starting about start of solar cycle 23 but this is highly contentious. Let’s carry on with the next exhibit.
This was a shock, unexpected: to a large degree Arctic and Antartic sea ice extent have a complementary increase in excursions post 2007. What on earth is going on? This suggests a global effect.
It then occured to me to do something unusual. Repeat figure 1.
This suggests a step change in variation, confirming eyeball MK1.
I don’t know why. An observation based on work not shown, is it possible polar ice varies much more during low solar activity? This is not entirely off-the-wall because of the solar magnetic linkage into polar regions and of UV into the outer atmosphere.
Post by Tim Channon, co-moderator
Data ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/ which is used by NSIDC and my trust is low.
This is about as awkward is possible, including a cantakerous FTP server.
Data is in subdirectories by named month Jan etc., time series as month values in two files in each of the 12 directories, eg. N_01_area.txt and S_01_area.txt for Jan which contains both area and extent. Format is a bit strange. Note there are missing months with data omitted, not marked and compensation has to be applied to some early data, details in the file header text.
Alternatively trust me (I don’t). I have code which computes a conventional time series and also deannualised versions. Looking at the code I think it is using whole dataset mean.
As usual for WordPress the only practical data format is XLS, spreadsheet is here (1M) with all additional results.