Cherry Picking 2 – Faking Global Cooling

 My previous post showed how you can get a series of downward trends in global temperature data, even though the overall trend is clearly upwards (courtesy of Skeptical Science.

The most frequent false claim about the data is that there has been no warming since 1998.  For a long time I’ve wanted to demonstrate explicitly the cherry-picking behind this claim.  Now here it is (taking advantage of some free plotting software I recently downloaded, and generating an animated gif at a free online site).

HadCruT temperature analyses

Here is an example of the false claim, from Australia’s former Senator Fielding, using the analysis of Bob Carter, well-known denialist.  It is purported to demonstrate that there has been no warming even though the carbon dioxide content of the atmosphere has been steadily rising.

Senator Fielding's cherry-picked temperature graph.

The animated graph above shows a sequence of data segments, and for each segment a straight line that is the trend for that segment.  The data are the so-called  HadCrut mean annual temperature estimates, from the Hadley Centre of the UK Met Office in collaboration with the Climate Research Unit of the University of East Anglia.  (Carter used monthly data above.)

Green:  data window 1998-2011.  The trend is nearly flat, which would mean there has been no warming.

Blue:  1996-2011.  By extending the data window back only two more years you get a clear warming trend, because 1996 was unusually cool, just as 1998 was unusually warm.

Orange.  Now let’s try cherry-picking the other way.  1992 was cool and 1998 was very warm, so the trend from 1992-1998 is very steep warming.

Teal.  Finally, if you use the longer data set from 1970 to 2011 you can see a clear warming trend, without any analysis.  You can see the other trends, based on shorter-term data, are misleading.

Climate scientists have stressed all along that to demonstrate global warming you have to look at longer-term trends, because there are short-term fluctuations that obscure the underlying trend.  You need at least 5-10 years worth of data.

You might still argue, from the HadCrut data, that global warming seems to have paused.  However these data do not include any allowance for polar regions, where measuring stations are scarce but warming is most rapid.  NASA’s Goddard Institute for Space Studies does include an allowance for polar regions, and their data are included in the following graph (magenta), with the HadCruT data for comparison (blue). [If the animation isn’t working, try clicking on the graph.]

In the GISS data the warmest years are 2005 and 2010, not 1998, and there is a continuing upward trend.  If there is an impression of slowing over the past decade, it is hardly any more pronounced that other “pauses” that you see, for example in 1978-1987, or 1987-1997.  These “pauses” are the basis for the escalator of the previous post.

Finally, we know 1998 was an exceptional year, because the strongest El Niño condition for a century was operating, and El Niño tends to raise the air temperature for its own reasons.  On the other hand for the past three years or so we’ve had persistent La Niña conditions, which tend to cool the air temperature.  This does not mean the Earth is not holding extra heat, it just means not as much is being held in the air.  The rest is presumably going into the oceans, which can hold enormous amounts of heat.  If La Niña ends, the air temperature is likely to jump again.

Anyway the case for global warming does not rest just on these temperature data.  Other direct measurements have now detected an imbalance between heat received at the Earth and heat radiated back into space.  Other symptoms such as ice melting in the Arctic and mountain glaciers give clear evidence.

There is a great irony in the denialists’ choice of the Hadcrut data to claim warming has stopped, because the Climate Research Unit (the “CRU” part) is the very one that supposedly faked its data, according to the Climate-gate myth.  (That’s the story, from emails illegally hacked from East Anglia University, that the scientists were trying to “hide the decline” and intimidate dissenters.  The emails were totally misrepresented and this has to be one of the biggest beat-ups ever.)    So not only do global-warming deniers choose the data set that suits them, it’s the data set they most vilify in a different context.

6 thoughts on “Cherry Picking 2 – Faking Global Cooling

  1. Hugh

    Dr Davies, thanks, but I’m not convinced. Even if GISS is the better view – and it may well be – the point is: is that warming outside or inside the margin of error? And even if it’s outside, what’s the anthropogenic contribution and what’s the contribution due to eg, recovery from the incontestable Little Ice Age? Personally, I want someone to show me these figures definitively before I consent to short term (ie decades long) impoverishment of hundreds of thousands of Australians. Is that wrong?


  2. Geoff Davies Post author

    Hugh –
    “I want someone to show me …”. I could spend my life trying to explain to people like you, one by one. The material is out there, much of it on this site, important stuff in the links I gave.

    No, reducing greenhouse emissions need not impoverish any Australians, that’s the other big myth. Again, look around the site … that is if you really have an interest in learning, rather than just harassing someone who upsets your view of the world.


  3. John Lavett

    The view that there has been warming since 1998 is falsified by the data and the flat line is not a result of cherrypicking. You might not like the fact but facts are facts.

    In the 5 or so years after the super El Nino of 1998 Climate Collaborators were happily referring to the year as proof of global warming. As things failed to continue to warm the truth that it was a super El Nino became the excuse for alarmists as to why there had been none to little warming subsequently.

    Collaborators choose 1979 as the start of their comparison, as this is when satellite data begins and, conveniently, is at a low point in the 20th century given then 1940s to 70s cooling period. This is also cherrypicking.

    Cherrypicking is not the issue, anyway. It’s clear that if one chooses the MWP or RWP as the starting point then temperatures are down. The main issue is that models have failed so abysmally to provide useful predictions about the future. The reason is that they overstate the influence of CO2.


  4. Geoff Davies Post author

    But the GISS data do not support what you’re saying. The El Niño-La Niña cycle does yield a significant correlation with temperature, so what you claim some ill-defined group might have said is irrelevant. The mainstream science still does not support the Medieval Warming Period being warmer than now. You’re relying on fringe science. There are several independent kinds of evidence, the case does not depend on “the models”.


  5. thewolf2010

    I think “science” works like this. You build a model or theory, you test its predictions against real data, and if it fails, you need to build a new model (and hopefully test it against “fresh” data. Admittedly, this is hard in Economics, and Climatology.)

    Anyhow, the past 10 years of data simply doesn’t fit the “theory”, and Dr. Davis doesn’t like that. While 10 years not fitting is insufficient to disprove much, it is clear that all the hype that was generated by extrapolations 14 years ago, should be put on a back burner.

    On a related note, Mr. (or Dr, if it hasn’t be revoked) Glieck’s behavior last week, goes a long way towards discrediting what comes out of “consensus scientists,” while providing fuel to privately funded scientists. Hate to paint with a broad brush, but when Mr. Davis includes his “expert” analysis of capitalism in his climate blog, I have to question his “objectivity” too…

    Did Mr Davis become an advocate of a centrally planned government funded global fight againts global warming because the science led him to conclude we need a huge socially funded project; or did his desire to find a huge socially funded project lead him to become a climate “scientist”?

    Lastly, my question for Dr Davis…just how despondent would you be if we experienced another 10 years of no global warming?


  6. Geoff Davies

    Wolf – learn to read, and spell my name.

    Look at all the data, including GISS, not just HadCrut. The past 10 years has shown warming. There has been a pause in the last 5 years, not unprecedented. Climate change is about long-term trends, as you allow.

    Where, in my writings on economies, do I advocate central planning and huge socially funded projects? I advocate a market economy.

    Thank you for questioning my motives, with no evidence at all, it distracts from addressing the substance of the argument. I have never received a penny for climate science.

    But if you’re concerned, what are the motives of ExxonMobil et al who blatantly spread disinformation in their own hundred-billion-dollar self-interest. This hoary old “scientific conspiracy” theory is pathetic.

    I would be immensely relieved, thank you for asking. However I might be concerned about the excess heat from the measured heat imbalance going into the ocean rather than the atmosphere, as appears to be happening now, and causing ever-more destructive storms. Until La Niña switched off.



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