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What value have forecasts ?

january 2002 - translated in august 2004

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Every time there is a debate on our future, and it is particularly sensible when discussing energy or transportations matters, it is unavoidable that someone will underline that such or such action is indispensable to face a "foreseeable evolution".

So we should build airports, because it is possible to "foresee" that air trafic will increase ; we should build additional roads because it is possible to "foresee" that road trafic will increase ; we must build additional power plants because it is possible to "foresee" that electricity consumption will increase, etc. It is then tempting to ask oneself to what extent is the future already totally written.

M. La Palisse wouldn't have said it better : the less unpredicted events there are, and the easier it is to make a prediction. For example, it is easy to "foresee" the trajectory of the Earth around the Sun for the coming years, because this evolution doesn't depend on many unpredictable elements, though an exception is the possible collision with a large asteroïd that would deviate our planet from its orbit. As long as we remain within the time bracket in which we are sure that no asteroïd will come close to the Earth's orbit, we can make a true "forecast", but when we go avoer the superior limit of that time bracket, then what we are talking about becomes just the "most likely outcome".

More generally, when a process is only driven by elements on which we have no influence, it is possible to use the word "forecast" : we can make such a forecast for the time it will take for the sun to consume all its hydrogen, or for the water height that we will measure in Brest at high tide on march 1, 2012. But when human action becomes part of the process, then we get unpredictable events all along the line. Is it possible to "foresee" that I will have three meals on febrary 6, 2015, because it is was generally happens ? No, one can deem it likely, but that's all : I might be dead, or sick, or in a train without money to buy a sandwich, or what do I know...

More generally, foreseeing human behaviour is always a more or less hazardous exercise, because it is not easy - if possible at all - to choose a totally trustworthy rule. When coming to human behaviour, then, most often what is presented as a "forecast", hence a non-negociable constraint for the future, is actually the sole result of our will of the moment, and as such can perfectly be changed if we wish it.

Let's take an example : we should increase the transportation infrastructure because the trafic is born to increase. Actually the only thing that we know for certain is that it grew up to now. Provided the evolution rules remain the same, it will indeed increase in the future, but we are the ones that decide whether the rules remain the same ! In other terms, what is presented as a "forecast" should be called instead "prolongation of the present trends". It consists in prolongating in the future the rates observed in the past, with, as the case may be, minor corrections here and there to take various considerations into account. Using the word "forecast" then bears a perverse effect, because such an exercice, that just reflects our wishes of the moment, will yield a result that everybody will consider as a certainty.

Indeed, supposing that the evolution rules will remain the same in the past is already a conclusion : it results from the hypothesis that the world must - or will no matter what - evolve just the same way in the future that it did in the past, which is no minor conclusion, and sometimes can be discussed !

Life expectancy : an observation before a forecast

Life expectancy at birth defines the probable age at which individuals will die. Well the only thing that we know for certain is the age of the people that die today, and going from that dataset to a "life expectancy" supposes that the rules will remain the same :

no increase in infant mortality (that could result from new diseases or some outbreak of existing ones, of a rapid increase of some kind of congenital malformation due to some specific pollution, etc...)

no outbreak of diseases (particularly deadful flu, new retrovirus, etc)

no all out atomic war


Just the same, demography is predictable just as long as no major outbreak (that will eventually happen, because microbes adapt much faster than we do) impedes the "forecasts".

These notions should therefore considered as probabilistic : that the population increases by 2050 is what is "thee most probable", not what is certain !

Presenting the result of a prolongation of the trends as an element that should be a non negociable constraint for aanyone, it is - voluntarily or not - switching hypotheses and conclusions, and bypassing the discussion on how the world should evolve.

Let's come back to our previous example : building roads would be a necessary pain, in order to satisfy the trafic increase, an evolution that no-one would control and that would be "unavoidable". But if the trafic increases, it is definitely because we (we = you, me, your neighbor, etc) wish to drive (or be driven) more and more ! Do we really want it, at any price ? If yes, we should then build roads not because "the trafic will increase no matter what", but because "we wish it explicitely" (and that definitely implies that trafic will grow !). The first way to state things allows - conveniently ? - to avoid to designate anyone as responsible for the observed trend ; the second - and correct - one clearly shows that the "forecast" is actually a wish, and that building new roads then corresponds to the way to meet it.

Often, supporters of such "forecasts" say that we were right to build new roads, since the trafic did grow. But the reverse would also work ! I could foresee that "trafic will decrease", then suppress one road out of two (that would not be necessary any more since the trafic is bound to decrease), and, without any doubt, the trafic would decrease, because of the saturation of the remaining roads (and it happens that it is exactely the action plan of some european cities that intend to decrease road trafic : they generally turn some streets pedestrian, narrow others, etc). The "forecast" is therefore self-realizing both ways, which is surprising if we stick to the supposed meaning of "forecast", but stops to be if we remember that we should use "wishes" instead. The good question is then to wonder whether the wish of the policymakers is also the wish of the majority of voters, but it does not question the fact that this "forecast" is actually a wish of the policymakers.

Of course, this "forecast" of growth of the trafic is self-realizing as long as no limiting factor comes into action - limiting factors being for sure part of the real world, not of our mental universe : reduced availability of fuels, decrease of the population following an outbreak, rarefaction of raw materials.... (see some reading notes on the "Report to the Club of Rome").

Just alike, many "forecasts" regarding the world energy demand are nothing else that the consequence of a wish : that of having "developping" countries follow the same path that occidental countries, while these latter remain at the same consumption level. Even as a prolongation of the trends such a "forecast" is debatable : its fundamental basis is the wish of a species - ours - to see things "go on" as today, holding the known real constraints (climate change, for example, or availability of natural resources) as secondary.

The elements published by the IPCC indicate, for example, that it will be necessary one day to divide the world CO2 emissions by two at least to achieve a stabilization of the climate disruption. This is equivalent to saying that remaining perpetually above that level guarantees an evergrowing disruption, which is physically not possible in a finite world. Well it is precisely on this kind of impossible hypothesis that are based most "forecasts" published by various international bodies, with this curious consequence that the increase of the greenhouse gases emissions will afterwards be presented as unavoidable.

No big surprise there : by setting aside an element in the set of hypotheses (greenhouse gases emissions, it is pretty normal not to find it in the conclusion !

I could multiply the examples. So next time that you read that "it is foreseen that...", do not hesitate to ask yourself : who foresaw what exactely, on the basis of what hypotheses, and most of all are the latter legitimate ? You will then realize that, most often, the "forecast" (regarding the evolution of society) is in fact the exact translation of "take one's desires for reality" : looking in detail shows that there is no prediction, but a wish, or a postulate. And then it is of course possible to wonder whether the postulate, disguised as a "forecast", really represents the common will.


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