Small differences lead to cardinal errors

The Record | November 23, 2011

The butterfly effect, the notion that the beating of a butterfly’s wings in one part of the world can lead to a storm in another, was coined to explain one of the more significant discoveries of the past century: that very small disturbances can have very large consequences.

In the early 1960s a mathematician and meteorologist by the name of Edward Lorenz was working on the thorny issue of weather predictability, using a state-of-the-art 113-vacuum-tube computer and a set of 12 equations to model weather behaviour. One day, to study part of the model in greater detail, he re-ran an equation, starting in the middle of the sequence to save time. Unexpectedly the result diverged totally from the original solution.

The reason, Lorenz determined, was that in the original sequence the computer was working with a number to six decimal places (.506127) whereas he had typed in only the first three digits (.506). By the thinking of the time, such a small difference should not have resulted in such a divergent result.

Thus was born the scientific revolution called chaos theory, a paradigm shift in scientific understanding rivalling quantum or relativity theory and which, in the words of Kerry Emanuel, professor of atmospheric science at the Massachusetts Institute of Technology, “put the last nail in the coffin of the Cartesian universe”. The butterfly effect, that arbitrarily small-scale disturbances can create large-scale disturbances, killed the idea that science could ever produce accurate long-term weather forecasts.

I mention Lorenz because last month Cardinal George Pell cited his seminal 1963 paper – or, rather, cited Christopher Monckton citing it – as evidence that predictions about the effect of higher atmospheric greenhouse gases are impossible.

In support of this notion, Cardinal Pell suggested the IPCC’s 2001 Third Assessment Report agreed: “In climate research and modelling, we are dealing with a coupled, non-linear, chaotic system, and therefore that the long-term prediction of future climate states is not possible”.

How, then, did that report estimate, based on a range of scenarios, that by the end of this century the average global temperature would be 1.4 to 5.8°C warmer than 1990?

Part of the answer is found in the sentence immediately following that quoted by Cardinal Pell: “The most we can expect to achieve is the prediction of the probability distribution of the system’s future possible states by the generation of ensembles of model solutions. This reduces climate change to the discernment of significant differences in the statistics of such ensembles.”

If that is unclear, this explanation from Professor Tim Palmer, president of the Royal Meteorological Society, might help: “As well as explaining the underlying scientific reason why such forecast failures are inevitable in a chaotic system, Lorenz’s work provides a potential methodology to mitigate the problem. In particular, whilst individual trajectories are unstable to small perturbations and therefore unpredictable, the evolution of the probability distribution of the initial state is not.”

Lorenz was keenly aware of the conceptual difference in predicting weather to predicting climate, Palmer writes. “We now use his terminology routinely: predictions of the first kind are essentially initial value problems, predictions of the second kind are essentially boundary or forced problems. The problem of anthropogenic climate change is predominantly (but not exclusively) a prediction of the second kind: how are the statistics of weather affected by some prescribed change in atmospheric greenhouse-gas concentration?”

Which might be the reason Lorenz, who died in 2008, never joined the ranks of climate-change scepticism and is revered as the progenitor of modern climate prediction methodology.

That Cardinal Pell failed to grasp the implications of Lorenz’s work (or was simply unaware of them, having taken at face value the interpretation of a professional sophist with a track record of distorting the findings of the research he cites) is indicated both by his confusion of weather with climate predictability as well as his incredulity that a significant increase of atmospheric carbon-dioxide could possibly be cause for alarm, since “today’s total CO2 concentration represents less than one-twenty-fifth of one per cent”. In light of the butterfly effect demonstrated by Lorenz, this is what the cardinal might describe as a category error.

For these reasons, among others, I stand by my assessment that Cardinal Pell is not showing prudence in aligning himself so stridently with the contrarian scientific view regarding the probable consequence of releasing into the atmosphere, in a matter of decades, a good portion of the carbon that has been sequestered in the earth over many billions of years.

A number of correspondents have made the point that truth is not decided by consensus. Quite so. But nor is the search for truth advanced by arguments that are logically self-defeating.

One correspondent has suggested I refer to Cardinal Pell’s address regarding the “nine errors of fact” found in Al Gore’s movie An Inconvenient Truth by Britain’s High Court. Even better would be to refer to the primary source, the judgement by Justice Burton, who found Gore’s movie “substantially founded upon scientific research and fact” but was persuaded that “out of a long schedule of such alleged errors or exaggerations”, nine had merit. These nine instances were where the movie, “while purporting to set out the mainstream view”, itself departed from the consensus scientific view, as expressed in the reports of the IPCC.

Personally I can’t see the logic of anyone who fundamentally disputes the validity of the IPCC’s findings wanting to make this a debating point.

“There is no precautionary principle,” Cardinal Pell said in his speech. Yet the Vatican’s Compendium of the Social Doctrine of the Church suggests otherwise: “The authorities called to make decisions concerning health and environmental risks sometimes find themselves facing a situation in which available scientific data are contradictory or quantitatively scarce. It may then be appropriate to base evaluations on the ‘precautionary principle’, which does not mean applying rules but certain guidelines aimed at managing the situation of uncertainty.”

This requires, the compendium says, “making temporary decisions that may be modified on the basis of new facts that eventually become known”. Prudent policies based on the precautionary principle “require that decisions be based on a comparison of the risks and benefits foreseen for the various possible alternatives, including the decision not to intervene”.

Every effort for acquiring more thorough knowledge must be encouraged, “in the full awareness that science is not able to come to quick conclusions about the absence of risk. The circumstances of uncertainty and provisional solutions make it particularly important that the decision-making process be transparent”.

These seem, to me, to be the crucial issues. I hope the IPCC has it wrong, but nothing in the scatter-gun arguments of the sceptics convinces me the probabilities are with them, and that the moral and prudent thing to do is nothing, rather than taking cautious measures to ween the industrialised world off its addiction to fossil fuels several decades before it will be forced to do so anyway.

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