Thursday, June 7, 2012
I made a small and somewhat inaccurate contribution to another WUWT thread, this time on Arctic Ice volume, and a figure quoted by the Guardian which I found surprising. My error is explained here; Stoat's account of the matter is here.
Anyway, it made me realise that I should pay more attention to ice volume. Although I criticise the Guardian's 75% reduction since 1979 as a mild exaggeration, the mean reduction of 66% is still an impressive figure. So I downloaded the PIOMAS data, and put it through the anomaly visualisation program of my previous post.
Again there are two anomalies calculated - without and with trend adjustment. The trend this time is much larger, so you need to watch the units.
Here's the analogue of the familiar Jaxa plot with the fitted periodic annual curve. It isn't an anomaly, and there is no detrending. You can see the steady downtrend, and I've shown the y-axis based at zero, so you can see it isn't so far off.
2012 is marked in black.
Here is the anomaly plot with trend, shown over the years from 1979:
You can't now see where ice-free is, but the persistent trend is evident, with some recent acceleration.
Now here is the same data plotted over a one year interval. Again 2012 is black. The ice volume is pretty much as last year, which is bucking the trend a bit.
Plotting the anomaly after allowing for trend gives a similar picture, but note the lower y-range. Over the last two years, mid-year has been a marked minimum of the anomaly, but this year (as at end April) it has not yet started that dive.
Posted by Nick Stokes at 9:17 PM