William M. Briggs

Statistician to the Stars!

What can we learn about global warming from poor reporting?

From today’s Syndney Morning Herald comes the headline: “Global warming to impact health“.

First, by impact the reporter almost certainly means influence, a more accurate, but far less energetic and “actionable”, word. But never mind that. Our lesson instead comes from the story, one of a breed which appears almost daily in some major newspaper somewhere in the world.

But before we can get to it, you first have to learn, if you do not already know it, the definition of tautology. A tautology is a statement which is always true; that is, no matter what happens in the word, no matter what conditions eventually hold, a tautology will be true. Some examples: “Either it will rain tomorrow or it won’t” and “Marxism is a stupid theory or it is not.”

Here, from the article we are studying, is the lead sentence; it is a tautological fragment, “Rises in temperature produced by global warming could result in an increase in the number of people being admitted to hospital with kidney disease, heart disease and mental illness in Australian cities.” To make this into a grammatically correct tautology we need only add the implied clause “or the rise in temperature will not result in an increase, etc., etc.”

So the reporter has written something which is true, which will always be true, and will be true regardless whether mankind influences the climate or not. But he has written his tautology in such a way to show where his sympathies lie, much as I did in my second example. In any case, we have no grounds for criticizing the reporter on the grounds of accuracy. All such attempts, which I have seen from the skeptical community, are doomed to failure.

We now have to look at the “study” on which the reporter did his article. This will require some work from us, but it is exceedingly important that you understand this study, because it is entirely typical of academic work in this area. You will see more of its kind, and with increasing frequency, so it is imperative that you learn to recognize it and ascertain how to properly criticize it.

Here are the second and third sentences

The study, by a team of academics and senior health professionals from across the country, compared the number of hospital admissions, ambulance trips and the deaths in Adelaide during heat waves, with those in normal weather conditions.

The heat waves – defined as a periods of three days or more in which the average temperature exceeded 35 degrees – produced a seven per cent increase in admissions to hospital and a four per cent increase in ambulance trips.

They also tabulate rates of kidney disease and mental illness under non-heat wave and heat wave conditions, finding these maladies increase during heat waves.

Here is their argument: since, they conclude, more cases of some diseases are present during heat waves, and heat waves will increase with global warming, and that global warming is true, we will see more cases of these diseases.

The structure of their pleading is in perfect logical form, and is correct; that is, their conclusion is true given their premisses. I emphasize: you cannot criticize the form of their argument, since that form concludes something which is true. Or I should say, conditionally true. We will see more disease if it is also true that more cases of some diseases are present during heat waves, etc.

Are their premisses true? I will offer a series of alternate possibilities and likely faults, but I am sure to miss some, which I hope my readers will help supply.

Statistical sample criticisms:

  • Did the authors look through the data to find diseases that increased in frequency during heat waves? If so, it is highly improbable that if we look at future heat wave data, we would see the same high levels of the diseases, most would have “regressed” to their mean level. And other diseases that they did not study will be found to have increased in frequency.
  • What period of data was used?? Presumably, the epidemiology of these diseases have changed through time, certainly “ambulance driving” has.? The time series component to these data should have been accounted for.
  • How many diseases did they find that did not increase in frequency during heat waves? These should have been noted.
  • How many diseases did they find that decreased in frequency during heat waves? These should have been touted as benefits of warming.
  • What were “non heat wave conditions”? Cold waves? All other periods of time? If cold waves, then how many diseases increased in frequency during cold waves? These should have been touted as benefits of warming. If all other periods of time, then they have chosen a poor sample: cold waves should have been separated out.

Medical criticisms:

  • Are there rigorously clear and certain connections between humans living in heat waves and the diseases noted? If not, then the uncertainty associated with each should have been detailed.
  • Again, the diseases increasing in frequency under cold waves were ignored.
  • What benefits for other maladies are there for increased warming? It is foolish to say there are none, for, at the least, fewer people would die from extreme cold.

Technological criticisms:

  • It is not at all certain that, given that heat waves will increase in frequency, people will suffer in them as they suffer now. It is highly probably that technological advances will, for example, increase the availability and efficiency of air conditioning.
  • Medical science, too, will almost certainly increase in efficacy and, with high probability, lessen the number of people susceptible to the diseases under question, therefore, even if heat waves increase, the rate at which people suffer will decrease.

Global warming criticisms:

  • Even if global warming is true, it is not certain, and even unlikely, that heat waves will increase in frequency. Assuming the models which predict warming are accurate, they predict more warming at nighttime and a more evening out of temperatures (reducing the diurnal swing of temperatures) than an increase in severe weather. In any case, the uncertainty inherent in these forecasts of increasing heat waves must be taken into account, and it was not.
  • All other possible benefits of warming were ignored.
  • And, finally, the uncertainty that global warming will continue was not accounted for.

Every criticism I offered did the same thing: increase the uncertainty, or decrease the certainty if you like, that we should have in the conclusions, in my view, to such an extent that the study is nearly worthless, and should not have seen publication.

But the authors were not content with their “findings”, they progressed to naked speculation: said one of them, warming “might also bring a significant increase in previously uncommon diseases such as Dengue and Ross River fever to Australia’s rural communities” and that we “could see both a worsening of existing diseases as well as the spread of diseases usually associated with warmer region.” Of course, we could; it is mere tautology to say we could, but to offer such a prediction without evidence and without an expression of uncertainty can rightly be called fear mongering.

I hope you have learned a little about how to properly criticize studies of this type. But whatever other criticism you offer, you cannot say this study, and others like it, are “not science.” It is science, but it is bad science, poorly executed science, and irresponsible science.


  1. Reid Bryson, considered as the father of climatology (so bad he has terrible kids) has issued some advices to get a rudimentary global warming BS detector. More GW specific than yours but as well worth reading.

  2. – Was it just that symptoms increase during the suddenly warm weather, but a climate that warmed gradually over decades would allow the sufferer to get used to the increased heat and not require a trip to the hospital?

    – Were some people simply trying to get out of the heat and decided that a trip to the hospital would be nice since it is air conditioned?

    – Heat waves are usually noted for a lack of rain since a cold front is needed to bring rain. During heat waves, dust and pollen are able to build up on roads making them more slick especially after the first bit of rain that comes. How many of the increased admissions were due to car accidents? Were admissions at the tail end of the heat wave included?

    Sorry, but these were all I could add at this time.

    John M Reynolds

  3. Tearing apart popular press stuff is some of the most boring skepticism. I really prefer seeing analyses that reveal something. Like Burger and Cubash 05. ETc.

  4. Interesting stuff. My gut feeling is that the power, influence and profits of newspapers and television will wane as the internet rises, leading to more scaremongering language like this, with much emotional content but less in the way of cold, clinical FACTS.

    To paraphrase one newspaper executive “if it bleeds, it leads”.

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