AGW deniers in “statistically illiterate” shock

One of the most popular myths promoted by those skeptical about man-made global warming is that warming has stopped and, in fact, the trend has even reversed in recent years. This illusion largely stems from the fact that 1998 was an exceptionally hot year and 2008 relatively cool due to the respective el Niño and la Niña events of those years.
Despite the fact that the current decade is actually the hottest on record, that eight of the last ten years are among the twelve hottest ever and that ten years is in any case too short a period to represent a meaningful trend, this myth has been remarkably successful – it is not just the usual suspects who are promoting it, even the BBC seem to have been taken in.

Climate scientists and other interested parties have already attempted to correct this misapprehension based on science, unfortunately without much success, but now Associated Press has made an excellent contribution to the debate which demonstrates that the claims made by the deniers are nonsensical from a statistical point of view.

In a blind test, the AP gave temperature data to four independent statisticians and asked them to look for trends, without telling them what the numbers represented. The experts found no true temperature declines over time.

The AP sent expert statisticians NOAA’s year-to-year ground temperature changes over 130 years and the 30 years of satellite-measured temperatures preferred by skeptics and gathered by scientists at the University of Alabama in Huntsville.

Statisticians who analyzed the data found a distinct decades-long upward trend in the numbers, but could not find a significant drop in the past 10 years in either data set. The ups and downs during the last decade repeat random variability in data as far back as 1880.

Saying there’s a downward trend since 1998 is not scientifically legitimate, said David Peterson, a retired Duke University statistics professor and one of those analyzing the numbers.

Identifying a downward trend is a case of “people coming at the data with preconceived notions,” said Peterson, author of the book “Why Did They Do That? An Introduction to Forensic Decision Analysis.”

They also nailed the way the deniers have cherry picked the data to suit their agenda.

Grego produced three charts to show how choosing a starting date can alter perceptions. Using the skeptics’ satellite data beginning in 1998, there is a “mild downward trend,” he said. But doing that is “deceptive.”

The trend disappears if the analysis starts in 1997. And it trends upward if you begin in 1999, he said.

I doubt it will silence the deniers but we now know that on this particular question their arguments are both scientifically and statistically illiterate.

Hat tip: Climate Progress

3 thoughts on “AGW deniers in “statistically illiterate” shock

  1. It’s hard to know where to start. Perhaps with the small matter of the validity of data which has been ‘adjusted’ in ways which invariably pull down past temperatures and raise up recent ones, an incomprehensible result given the urban heat island effect, and the growing problem of siting recording stations sufficiently remote from tarmac, airconditioning units etc. A sixth grader in the US paired up stations less than 50 miles apart, and mapped out 100 or so contrasting readings. The result was a trend upward in the urban data, and a flat line in the adjacent rural stations.
    The CRU figures are of course subject to the ‘fudge factor’ – a set of value adjustments which pull down values from 1925-1940 (which period contains the missing four warmest years), and then pushes up values post 1950. Data from Australia and New Zealand has been ‘adjusted’ in like manner.
    However, even supposing we were to accept the twentieth century data, the issue is whether the current climate is or is not outside the normal range of variability. No one seriously denies that temperatures have risen since the very cold period 1500-1820. Thank goodness they have. Even now in Europe 7 people die of the cold for every 1 that dies from heat. The point is that we know from our historical record that conditions before 1500 were much warmer, and until the early 90s meteorological presentations showed that. The first IPCC graphs showed only post 1400 temperatures. This was AGW cherrypicking, was it not? The ‘work’ done by Mann, Briffa, and Jones has been focused on getting rid of that troublesome medieval warmth, on the basis of tree ring proxies that themselves break down when they meet the supposed recent warming from 1960 onwards, and have to be abandoned. If tree-rings are right 1000 years ago why are they not right now?
    I pay you the compliment of visiting your blog, and posting this, because you appear to be intelligent and rational. Here is some advice. Intelligent and rational people are often wrong. You seem to ascribe to ‘climate scientists’ (where you mean actually SOME of them) a godlike invincibility, when they are attempting to interpret and predict long term developments in a system they still cannot reliably forecast more than three days ahead, even on a strictly local basis. Even if they were completely disinterested, scepticism would be required in our response. describes the difficulties involved in predicting the interaction of rockets with the relatively simple force of gravity, and compares them with the imponderables of marshalling climate data. But they are not disinterested. I have already pointed out to you that funding from government and other official bodies highly disposed to favour AGW outweighs by $billions to $millions that from ‘Big Oil’ or whatever synonym for ‘Pure Evil’ you favour. AGW is the gravy train. Everyone has short term vested interests, even if they consist of sounding ‘concerned’ at a dinner party.
    One final point. The scientists you quote have the courtesy to refer to those who disagree with them as ‘sceptics’. You begin by referring to those who are ‘skeptical’, but soon fall back on ‘deniers’. The terminology here betrays your own ‘preconceived notions’. ‘Denial’ is usually used to refer to people resisting truth, when in fact all you have is a hypothesis. Adding in the associations of the word with holocaust denial makes the term an offensive insult.

  2. Stephen,

    Thanks for your comments, apologies for the delay in replying.

    Firstly I’m afraid I just don’t accept your view about the validity of the data. We have had a lot of accusations and innuendo but no actual evidence that any data has been manipulated. Furthermore there is no credible reconstruction that puts temperatures pre-1500 warmer than today. What “historical records” of actual global temperatures are there that show this? Anecdotes about Romans growing grapes in England and Vikings settling in Greenland are hardly evidence. As for tree rings – despite the divergence problem shown by some datasets they match the pre-1960 instrumental records pretty well, as well as other proxies for past centuries, so there are good grounds to believe them to be reliable for older periods.
    I don’t believe climate scientists to be infallible but as I do in any other subject I have due respect for their expertise and see no reason to give more weight to the opinions of those less qualified. If I’m ill I go to my doctor, I don’t take the advice of some guy on the internet who has a plausible suggestion.
    On the point of funding, I don’t know why you think official bodies are pre-disposed to favour AGW and governments would still fund scientists to study climate regardless of AGW, it’s an entirely neccessary field of study.
    Finall of the “denier” thing – I have spent a great deal of time debating AGW in the last couple of weeks and have always been polite and respectful to those I have argued with but there are some well known voices who are just contrarians, who persist in spouting anti-scientific nonsense which has been debunked many times before, the likes of Mel Phillips, James Delingpole, Christopher Booker, Ian Plimer. they are propagandists uninterested in the behind the issue and I have no problem in calling them “deniers”.

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