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Oh no, not the Hockey Stick again

Posted by softestpawn on July 30, 2009

The “Hockey Stick controversy” centers around a graph published by a Dr Michael Mann. It showed how temperatures had remained fairly steady, until mankind started burning lots of coal and oil after which the globe heated alarmingly:

ClippedFromIPCC

Because the world is mostly American, it’s an ice hockey stick rather than a real field hockey stick. The long steady decline is the hockey stick handle, the sudden rise the blade:

Ice Hockey Stick

The wiki article linked above outlines the main arguments about whether it’s valid, but there are a couple of other interesting things.

It became centre-piece to the IPCC 2001 report appearing in the summaries, and featuring (if I recall, I haven’t counted recently) eleven times throughout the complete reports.

That overt, specific and limited selection raised skeptic alarm bells. If there is overwhelming evidence for something, then you expect to see overwhelming evidence. Not a focus on one graph from one paper.

1998 as an end date

The first ‘interesting thing’ is that the graph stops in 1998, an unusually warm year, with an end temperature of around 0.7C above the 1961-90 baseline, which is indeed worrying.

Now that’s just a matter of timing rather than fraud (Mann et al’s paper was published in 1998). But by the time the 2001 IPCC report was released it was clear that 1998 had been unusual; 1999 and 2000 were only around 0.25C according to Hadley (0.35C according to GISS).

This rather makes a mockery of the complaints about ‘deniers’ using 1998 as a start point to show that the world is cooling. It’s not right to cherry pick such a year to show a trend now, and it wasn’t right for the IPCC to do so then.

It also indicates a bias in Evil Big Climate; observations that show unusual warming are accepted and published with warnings of runaway effects. Observations of unusual cooling – as in early 2008 – are bounded by warnings of temporary anomalies and ‘noise’

Consensus? What Consensus?

More interestingly it ran counter to the existing ‘consensus’ that there was a medieval warm period and a victorian ice age, supported by various accounts and proxy measurements dotted across the globe.

Which makes a mockery of the warmists cry that a ‘consensus’ should be accepted, even putting aside that a ‘consensus’ is not a measure of scientific fact.

The new Hockey Sticks

The arguments between McIntyre et al and Mann et al led to that particular Hockey Stick being abandoned, and the results of some new studies were collected into a new iconic graph:

As you can see these – and particularly the later ones, coloured red – are no longer Hockey Stick shaped; there is no long straight handle with a marked sudden change at industrialisation. Nevertheless these are called ‘hockey sticks’ by the faithful in memory of the original one.

All that is left is the blade, and even that is artificial. Despite including studies up to 2005 (click on the graph to see the references), the Big Black Line of recent temperature records stops at the steep slope we saw in the unusual year of 1998.

The Latest Hockey Stick

And still there’s some ‘interesting’ choices being made for graphs, these easily-understood, easily-published, easily-misleading summaries of evidence.

Recently Mann published a new one in September 2008:

MannsNewSticks

We can see the medieval warm period and victorian ice ages are returning, more pronounced. The big red line at the end, forming the blade and shooting up past 0.8C by the year 2000, is based on Hadley’s CRUT land only dataset. The grey line hidden behind it is Hadley’s official global temperature estimate.

However CRUs global monthly and average (land) temperatures only break 0.8C in 1998; the average for the subsequent ten years between then and the study being published is 0.6C. Which would put the end of the red line on the graph, rather than have it shoot off into the infinite unknowns in 2000.

(The baselines look similar: CRU land only just passes its own 0C baseline in 1945 according to those records and similarly does so on Mann’s graph).

But the past proxies are not all land only; the black line is land+sea, Moberg 2005 combines ocean and lake data, and Mann and Jones 2003 is of mean surface temperature. So if we replace the red line with Hadley’s global temperature estimate, we get something like this instead:

MannsNewSticks_640_fixed

which, while “unprecedentedly high”, is not quite so alarming.

(Not that we should read too much into the temperature records alone)

With thanks to Sophist et al at Bad Science. See also McIntyre’s more thorough castigation of the original

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One Response to “Oh no, not the Hockey Stick again”

  1. Fred said

    Thanks for the pointer here in comments over at the ninthlaw. Interesting.

    I think the ice core temp proxy record is especially valuable for considering how Earth’s climate has varied in the past. I highly recommend J. Storrs Hall’s post over at Foresight Institute.

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