Thursday, June 25, 2009

First ARCUS summary of 2009

The first sea ice outlook from ARCUS is now out. Have a look at the full report at the link. You'll see my name there, with what turned out to be a boringly typical guess. Actually, we all seem to have been pretty much of the same mind as to amounts, and to distributions around those amounts -- somewhere about 4.9 million km^2, with error ranges of about 0.5 million km^2.

The interesting part being that we arrive at such similar estimates for both value and variation around it by such different means. Do look at the descriptions of how groups arrived at their predictions. I'll spend more time here on my method later. The only particularly different guess (3.2 million km^2) was from a group (Arbetter et al.) that provided 2, and labelled the other one (4.7) their outlook prediction.

2 comments:

S2 said...

I think that a figure of 4.9 million km^2 would put us more than two standard deviations below the linear trend for the third consecutive year.

I'm no expert on statistics, but this would seem to suggest that the trend is no longer linear. Either there has been a step change, or the melt rate is accelerating.

Am I missing anything here?

Penguindreams said...

Not really. All the predictions were based on something other than continuing a linear trend.

Some of the ARCUS estimates were model-based, so wouldn't know about trend lines anyhow.

The statistical ones, like mine, assumed something other than a simple linear trend. The only person who seems to want to take a linear trend is
William Connolley
(see Belette, June 2, 5:11 PM), but he's not so enthusiastic about that method as to have taken up my offer in "Connolley-Grumbine sea ice bet" (not even cash riding on it).