Hi

No it's not the IPCC assessment it's me with some more stats!
I know without seeing any graphics this is a bit like describing a game of snooker on the radio - so it might be easier to look at the images which you can find he http://xmetman.wordpress.com/

I’ve extended the work that I’ve been doing into the downloading the Arctic sea ice data made freely available from the National Snow and Ice Data Center in Boulder and which I blogged about earlier this week.

Method

With the data that I had already obtained by parsing the files I had downloaded from the NSIDC, I calculated the following statistics:

(1) Average extent of sea ice by meaning every available day of the year.
(2) The percentage of the 1979 annual average.
(3) The date and extent for the maximum extent of sea ice for that year.
(4) The date and extent for the minimum extent of sea ice for that year.
(5) The number of days between the spring maximum and the autumn minimum (melt days).
(6) The total ice gain and loss from the previous season and the balance of the two.

I inserted the statistics into a data grid and then plotted them into four separate graphs.

(1) A line chart (1979-2069) of the mean and annual extremes, along with a linear regression trend for each series.
(2) An area chart (1979-2012) of the length of the Summer melt season in days a long with an average of the entire series.
(3) A bar chart (1979-2012) of each years gains and losses.
(4) Another area (1979-2012) chart of the changes compared to the 1979 annual
average.

I purposely didn’t plot either the first and last years because they are incomplete years and screw the charts up! I did add forecast values to the first chart from the values I obtained from calculating trends for the maximum, mean and minimum ice extents. I added them till the Autumn minimum fell to below zero which it does by the year 2069.

Before I get blitzed with complaints (that’ll be the day) about why I did this, I will freely admit that the logic behind doing this is more than a little bit dodgy. I know nature doesn’t like straight lines and that’s what linear regression give you, but the I thought what the heck and just did it anyway. I’ll also add that my calculations don’t take into account the year 2013 so they may be slightly out when I do make a calculation when this year is finally in.

I also added a couple of image controls to compare the Arctic sea ice at its Winter maximum and it’s Autumn minimum. I did this by picking up the images directly from the NSIDC before archiving them so I could use them next time I ran my BioGraph application without having to access the internet again.

Results

The decline in maximum, average and minimum sea ice is pretty uniform. We are already at just over 15% lower in 2012 than we were in 1979 using the annual average. If you look at the forecast trends for the year 2069 will mean that the annual average will be a third of what it was in 1979, and the autumn minimum will be 0%, meaning an Arctic clear of late summer sea ice in just 56 years time.

The Summer melt season was interesting and varied enormously year to year. I don’t know if I’ve got these figures right but in 1997 the melt days were 168, the next year 1998 they shot up to 205, before falling again to 167 in 1999. I did read on the Met Office that storms in the the Summer can have a pretty dramatic effect on sea ice either one way or another.

The third graph shows the gains and losses over the last 35 years or so. This year (if you look at the table we have a net gain of 1.7 million square kilometres in sea ice which reverses the losses of the last 3 years. As always please let me know if any of my calculation look a bit dodgy and I’ll put the right.

The fourth and final chart just shows the difference in the annual average since 1979. This may look at odds to the last graph but this is due to the fact that I’m calculating a unique value for an entire year rather that just looking at extreme values.

Conclusion

Apologies to the NSIDC for me fiddling with one of their images! I think the point of this blog is that anyone can make an educated guess at the future of the Arctic sea ice in the summer with a little bit of work, it may be unscientific but I did it without the help of a super Cray computer (or whatever they use nowadays) and came to the same conclusion that the IPCC have come to in their latest assessment – but cleverly I don’t think they specified a year!

Bruce.