The previous blog post dealing with area and extent had a bit of a wordy introduction, so I'm doing a small follow-up showing the different graphs made by commenters and myself.
First of all the very telling graph by Larry Hamilton:
Update: Larry Hamilton has updated the graph with July 2010 data and says the following in the comment section below:
July or August, not September, comprise all of the low points in the area/extent curves (except for an odd double-dip in 1995). FWIW, in the past 3 years August has been the low point.
July 2010 looks similar to July 2007, by this metric.
As area and extent have been in decline over the past 30 years, one might have expected the percentage you get when dividing area by extent to stay roughly the same. But that isn't the case. Larry's graph shows that area/extent percentage has been in decline over the past 30 years, which in my view can only mean one thing. Or two things actually. First is that because of higher air temperatures in the Arctic in some years, like 2007 and this year, more melt ponds show up earlier in the first part of the melting season (check Tamino's post which has a graph that shows this). But more importantly around this time in the melting season - when the percentage reaches its bottom - area and extent diverge in such a manner that it says something about the interior of the ice pack. The ice seems to have become so thin that it gets pushed around more easily, causing 'holes' to appear in the ice pack's interior.
As it says in the graph, Larry has used monthly NSIDC data. Another commenter FrankD has used IJIS extent data, deduced IJIS area data from their area graph (no downloadable data yet) and combined them to produce this graph, showing area/extent percentage during the melting season:
I've decided to man up and make my own graphs, as I want to use the area/extent percentage graph for the SIE updates until the end of the season. I'm hoping IJIS will answer my mails asking them for area data, but in the meantime I'm using IJIS extent data and CT area data and combine them to make graphs such as these:
Here's the graph for the 6 months that are most interesting:
And here's the graph for the whole year:
If you want, you can look at and download the spreadsheet I've made. I've ordered all the data, removed the -9999 cells with more realistic numbers, and did a very naughty thing by removing Feb. 29th 2008. I just can't handle those leap years. Don't tell Tamino!
I end with the PIOMAS graph that was updated a few days ago. Although extent seems to drop relatively fast in the past 4-5 days, which boosts up the area/extent percentage, the graphs above might be a first confirmation of the anomalously low volume the PIOMAS model is showing:
Update August 5th:
I have received an answer from someone at IJIS:
In our webpages, only the graph and csv data of Arctic sea-ice extent are
released to the public. Regarding the graph of Arctic sea ice area, it is prepared
tentatively only for research purposes because the sea-ice area can have much
more errors than the extent has due to the effects of melt pond etc. in summer.
So releasing the area graph and csv data to the public might cause a confusion.
This is our current policy for the sea-ice monitor web.
Thank you for your understanding.
This reminded me to insert a caveat: these graphs are interesting and fun to make, but not conclusive in any way. :-)