Comments on: Short memories redux

By: Two graphs you probably won’t see at Andrew Bolt’s blog - Pure Poison

Thu, 06 Aug 2009 00:47:58 +0000

...] have noted before that cherry-picking short-term trends in data – and scrupulously omitting mention of the same data [...

By: monkeywrench

monkeywrench — Wed, 10 Jun 2009 01:56:14 +0000

From the same NSIDC pages, this graph is slightly more convincing of the long-term trend. For those familiar with the "graphing" approach to the stockmarket, if the sea-ice extent were a listed company, the downward trend of the successive peaks spells a sick business model. In my opinion, anyone professing a science background who knowingly ignores data that fails to reinforce their political viewpoint is a fraud.

By: dam buster of Preston

dam buster of Preston — Wed, 10 Jun 2009 01:25:15 +0000

Nice post TZ – Interesting to note the slight variability even between the two graphs.

By: gregc09

gregc09 — Wed, 10 Jun 2009 01:20:15 +0000

I imagine it’s a danger with using one piece of evidence as the basis for supporting a position – the temptation is going to be draw out the bits that agree with your preconceptions. Something we all do, I suppose.

Those pictures could be used either way, as you say. A climate-change skeptic might point to the apparent ‘reversion towards the mean’ from the 2007 low – each year’s line looks on the face of it to be moving back towards the ‘norm’ based on the 1979-2007 period. While a ‘climate change believer’ might see just that all three recent year’s are below the norm. It’d be interesting to know what is typical for other unusually low years – say those that occurred during the 1979-2007. Chance are they might also show some reversion to the mean. I doubt that each year is independent of years immediately around it. A year where the Ice level is high/low is likely to be followed by other years that are high/low, but perhaps not so much so if it takes time for ice to melt or new ice to form. That’s a novice’s view, anyway… this novice, at least.

Besides, even the 1979-2007 base period for setting the norm is pretty short – only 29 years. The standard deviation estimate based on that is going to be pretty noisy, particularly if each year is not really an independant observation. So it would be hard to say anything with confidence based on those pictures. It’s when the evidence from a variety of sources is put together that the picture gets much stronger.