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Getting cute with graphs

How to cherry pick data

Here’s the banner image for the Global Warming Policy Foundation, Nigel Lawson’s ‘think’ tank.


On the left of the image, that’s a cute data plot of 21st Century global mean temperature (2001-2008), and, plainly, it shows that the temperature is in decline over the seven year period.

But why only seven years of data, and not 130 years of data? For the forward looking chaps at the GWPF, one supposes that would be just too last millennium.  It’s 2010, after all. Why look backward?

Here’s why not:


The Global Warming Policy Foundation got it right with their banner image; that is how to cherry pick data. Don’t show, don’t even hint at, the existence of something that contradicts your message, like 130 years of temperature data with a really clear positive trend. Just ignore it or deny it.

How not to cherry pick data

With that in mind, take a look at this really quite baffling graph from the website of the Orwellian-named Canadian ‘Friends of Science’:


This series runs from 1979 to 2009. It shows data from two averaged satellite temperature records, with the CO2 concentration in green. Both birds have only been flying since the end of the 1970s, hence the data series starts in 1979. “Surface temperature data is contaminated by the effects of urban development”, the ‘Friends’ tell us, which one supposes must suffice as explanation for their only using satellite data. As an aside, one wonders if science really needs such friends as these, able to dismiss 130 years of surface temperature measurements and scientific endeavour with an imperious wave of the hand. But let us persist, and see what the satellite data shows; perhaps a best fit over the 30 years of satellite measurements will reveal some interesting information.

Well, the ‘Friends of Science’ were good enough to plot a best fit (that odd little purple line on the right), but one that started on January 2002, not 1979:

“The best fit line from January 2002 indicates a declining trend.”

Indeed it does, dear ‘Friends’, but why a best fit for that interval? 1998 to 2009 would have really made your point. Plotting a best fit from 2002, while plainly ignoring the rest of the data, just looks silly.

Where the ‘Friends of Science’ went wrong, clearly, was in revealing the existence of a  full 30 years of satellite temperature measurements. If their x-axis had started in 2002, it would have made for a much more subtle cherry pick than displaying 30 years of data and adding an orphaned best fit line that doesn’t cover even a third of the whole plot.

I don’t know, it’s as if the ‘Friends of Science’ aren’t really committed to denialism.

Take a tip from the GWPF’s playbook: if you are going to cherry pick data, don’t blatantly show the audience that is what you have done, and don’t even hint at the disconcerting existence of such findings as this:



4 Responses to “Getting cute with graphs”

  1. I do love the manner in which you have framed this specific problem and
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  2. Norm says:

    HadCRUT3 showed 0.07°C decrease in global temperature since 2002 and even when ‘revised’ to HadCRUT4 by the “climategate group” at the Hadley Climate Research Unit this global cooling since 2002 still showed up forcing the Met office to admit that net global warming has been zero since 1997.
    This means that when the world leaders met in Kyoto Japan in December 1997 at the IPCC Climate Summit they signed on to the Kyoto Protocol to stop global warming after global warming had already ended.
    On December 17, 2002 Canada ratified the Kyoto Accord after the world had already started cooling
    On February 2 The IPCC released the summary for policy makers falsely stating that:
    “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level (see Figure SPM.3). {3.2, 4.2, 5.5}”
    And if you are going to talk about cherry picking the 2007 SPM continues with the statement “Eleven of the last twelve years (1995–2006) rank among the 12 warmest years in the instrumental record of global surface temperature (since 1850). The updated
    100-year linear trend (1906 to 2005) of 0.74°C [0.56°C to 0.92°C] is therefore larger than the corresponding trend for 1901 to 2000 given in the TAR of 0.6°C [0.4°C to 0.8°C].
    From its first value in 1856 to November 2013 HadCRUT4 shows just 0.73°C of net global warming, and with the world now cooling since 2002 and expected to cool at least until the end of solar cycle 25 around 2032; it is perfectly clear the increase in CO2 emissions from under one gigatonne in 1856 to over 35 gigatonnes today did not and actually could not cause the catastrophic global warming claimed by the IPCC!

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