By way of a change we start this month’s look at all things Arctic with some sea ice statistical analysis. Anthony Watts’ Arctic porky pie production line has been speeding up recently, and I am not the only one who has noticed. As part of his takedown of the latest “skeptical” allegations against the United Kingdom Met Office Tamino has been looking at trends in Arctic sea ice extent over at his “Open Mind” blog:
First and foremost, the yearly minimum is only one day out of the year. We have sea ice extent data throughout the year, and what happens during the rest of the year counts. Instead of using the annual minimum, let’s use the annual average. To avoid losing the most recent data, I’ll compute the yearly average for October through the following September rather than the usual (but arbitrary) January through December. I’ll also omit October 1978 through September 1979 because that year is incomplete. I get this:
The annual averages show much less fluctuation than the annual minima, so we can estimate things like rates of change with greater precision. I find that there is statistical evidence that the rate changed over time. One model of such changes uses three straight-line segments with their changes chosen to best-fit the data, like this:
