Towards a Better-informed Climate Debate

Informed debate on climate change is hindered by naïve interpretation of trend data. I have more confidence in the understanding of stock-market traders than in that of most climate change commentators

The more I look at the arguments on climate change, the more concerned I am at the crude misapplication of statistical methods that I find in them. This note is at least as reliable as views being expressed by many major contributors to the climate debate.

Lies, damn lies and crappy statistics

How much faith do you have in statistics? If you have formed a view on climate change, you should at least also have a view on what can and can not be concluded from a statistical examination of a database. And on the credibility of the analyses made by other commentators. My position is this. Statistics are generally considered to be the collection, analysis and interpretation of data applying various mathematically derived methods. That will do as a working definition. Data is plural of a datum. Data are the bits of stuff collected – the daily temperature readings from a weather station for example, or for a patient in hospital, or the price of a Corporate stock. As a matter of fact all of these data look rather similar when visualized as a time series.

We are pretty sure that the fluctuations of the patient’s temperature will ‘spike’ but in general will return to a standard basal level. Stock-prices as we know too well are less predictable. And as for charts of data about climate change, well these are in a different class altogether.

The First law of statistics

The first law of statistics for me is that statistical interpretation has to follow statistical understanding. Opinion is OK, informed judgement is different from opinions. Public debate tends respects the rights of individuals to express honestly expressed views. Phone-in programmes and the majority of blogs are not much more than that.

The second law of statistics

There is no safety in numbers if you don’t know what they mean. This brings me to one difference between climate debate numbers and those stock market and patient temperature charts. Climate debate numbers are increasingly highly complex abstractions which have been developed to examine a theoretical model.

The third law of statistics

Correlation is not the same as causality. My old statistics teacher used to quote the example of storks found perching on houses with the greater number of children born in them in one study. There was a correlation (perhaps because big warm houses attracted storks) but not one which can confirm a causal relationship between stork presence and human birth data.

The fourth law of statistics

Trend lines are treacherous.

I base this on the mathematical fact that there are a very large number of ways of drawing a line through thirty of so data-points. The zigzags of the data points are smoothed out in all sorts of cunning ways. The simplest smoothing is a straight line. It invites you to decide what all the deviations from that straight line mean.

A simple illustration

I have been playing around with a simple way of visualizing trend data. Let’s take the yearly data on temperature changes over a thirty year time period, the recent battle-ground in the climate debate

Many charts have appeared showing a trend as a straight line (so we have to beware of the fourth law). I find the following little thought-experiment revealing. Take a thirty point trend chart and select the highest and lowest items on the chart.

Mentally add each point in turn as the first datum of the chart. Almost always, one or both new visualizations change your perspective of the trend line and where the chart is going into the future.

Now repeat the experiment with each of the same two points in turn at the end of the trend chart. You will again find the visualizations offering one or maybe two fresh perspectives

Doesn’t that just confuse the issue?

Maybe it does. It weakens confidence in just what the trend-line might be telling you. But perhaps a bit more confusion and a bit less conviction is what is needed at the moment. Anyway, I do hope you will be able to contribute to more productive discussions on climate change in future.

Notes

I am no Fellow of the Royal Society of Statisticians, but I check my views from time to time with someone who is. The post captures my beliefs as a relative outsider to the Climate debate. I am suggesting the ‘laws of statistics’ in the sense of guiding principles on which I develop my case, rather than universal truths. Nor am I suggesting that visual inspection of trends is a substitute for careful application of statistical testing. But developing skills of visual inspection may enable more people to develop a sense of what a trend-curve might be signalling, and have a more informed discussion with those generating and interpreting such data.

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8 Responses to Towards a Better-informed Climate Debate

  1. Alex Hough says:

    The DebateGraph for the summit [1] looks interesting. Its a collaborative mapping tool. Stats have yet to be covered…

    [1] http://www.copenhagensummitmap.org/

  2. Babis Theodoulidis says:

    Very good topic and close to my heart!

    I agree that statistics can often be misapplied and visualised in a way that leads to the interpretation we aim for.

    However, the problem as I see it, is not in the statistics (analysis and interpretation). It is in the data and the observations that capture this data. To have confidence on the statistical analysis and its interpretation, it is important to have confidence on the data and the measurements that created this data (the observations) in the first place. This goes beyond your “second law of statistics” by emphasizing how data have been obtained (their quality aspects)rather than only what is the meaning of data.

    It is also important that data are available for everyone to access and use especially, if they are collected with taxpayers money. The speech by the Prime Minister on the topic of “Smarter Government” today is a step in this direction (see http://www.number10.gov.uk/Page21633) and more of this is yet to come once the “linked data” initiatives start producing results.

    Babis

  3. Tudor says:

    Thanks to Alex and Babis for enriching comments.

    Alex, The Climate map looks a worthwhile project. It reminds me of an up-market Wikipedia process.

    Babis, I don’t think we are far apart, and I agree about finding ways of communicating/explaining research methodology. Hope you got as far as my apologia regarding the provisional nature of the ‘laws’ I proposed.

  4. Tudor,

    I have done very little serious reading on this issue — and “my-self psycho-analysis” (which is always dangerous) suggests that the reason is that I am possibly a sceptic in terms of the effect of humans on climate change!

    But, why am I sceptical? It is strange, because for most of my working life I have been a data-orientated economist and very interested in public-policy issues.

    I think it is because I smell a psychological rat!

    Rather than focus on the data, why don’t you now focus on the psychology of it: is it essentially a scare campaign (similar to political) and supported by many “experts” (some true belivers, and others as careerists) or is it “real”?

    Jeff

  5. Tudor says:

    The more I look into this, the more layers of uncertainties I find (The Russain Doll effect?).

    I’m currently of the view that that the dominant view (warming with significant reversible component) is held by the more of the more credible scientists, but that the sceptics (scepticism a better word than denial) have identified the hyperbole in the dominant position as communicated in the media.

  6. Cordell says:

    Two things I would like to add to this discussion. The first is an excerpt from Tudor’s book on Leadership Dilemmas – from page 15 “Do I trust this “expert” or do I trust my own judgement” – how fitting. The second is in regards to the above comment regarding the more or less credible scientists & sceptics – try listening to Clive James’ “A Point of View” from last Friday (11 Dec). http://www.bbc.co.uk/iplayer/console/b00p6vln

  7. Tudor says:

    Thanks for that comment. Did I write that? Memory fades, but it sounds part of as point I think we were making about ‘ reading’ of an expert’s ‘map’ and ‘testing’ the map.

    Applying the ‘map-testing’ I enjoyed Clive James (as I usually do), but did not agree about his assumption that there is widespread and dogmatically-held scientific agreement on climate change. Maybe he is selective in his reading.

    The consensus being reached is that something is happening to the global climate, partly at least through human activities.

    If there have very few credible scientific voices raised in support of the various views which contain a contrary position, this need not lead us to conclude that a community of scientists are engaged in some conspiratorial collusion.

  8. Cordell says:

    Interesting, I didn’t interpret it as you did. The way I heard it, he made no assumption of a widespread agreement on climate change, on the contrary. What I heard was that the media had in many ways promoted the doomsday “side” and ridiculed any nay sayers.
    I thought his arguement was more about how the recent “Climategate” issue from the University of East Anglia would merely open up the debate to be held in public, where it should be held.
    I do not believe that there has been any collusion either, only that any scientist who does not agree with the mainstream “opinion” has been sidelined by the media. Maybe because if it weren’t man made then it wouldn’t sell many papers…

    Sorry – I’m not a fan of main stream media and I believe they have a lot to answer for, this broadcast just added to my belief.

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