‘Have you seen how much Giovannino has grown? If he carries on like this, by the time he’s twenty he’ll be at least three metres tall.’
The absurdity of this statement is obvious.
Yet it is very similar to the way predictions about the future are often constructed. A real trend is observed, extended with a ruler, assigned a stratospheric speed, and everything else is implicitly assumed to stand still.
This is a common error in demography, economics, epidemiology, environmental science and even politics. It lies not in observing a trend, but in forgetting that the system being observed will continue to change.
In recent decades, communication about climate change has offered several examples of this mechanism. Al Gore helped popularise cinematic images of coastal cities destined to disappear beneath the sea. Greta Thunberg has chosen metaphors with great communicative power and little predictive value, such as ‘our house is on fire’.
Messages of this kind have had the merit of drawing attention to a real problem, but they have often also conveyed the idea of a linear, inevitable process that meets with no response.
Reality is usually more complex. Coastlines evolve as a result of rising sea levels, but also of currents, sediment transport, subsidence and human intervention. In some areas they retreat; in others they advance. These changes depend on the interaction of many factors, not on the unimpeded action of just one.
This holds true for most complex systems. When a threat emerges, behaviour changes, resources are invested, new technologies are developed, rules and organisations come into being. Linear prediction describes a world that does not respond, whereas history almost always tells of a world that does.
Many epidemics follow precisely this pattern. If a disease were left free to spread unchecked, the consequences could be enormous. But people observe, study, isolate, develop vaccines, medicines and healthcare protocols. The outcome changes because the system changes. Smallpox did not disappear to spite the predictions, but thanks to countermeasures that altered the course of events.
The same happened with the major demographic predictions of the late 1960s. It seemed inevitable that population growth would cause widespread famine. Those projections implicitly assumed that agriculture would remain largely unchanged. Instead came new crop varieties, fertilisers, irrigation, mechanisation and levels of productivity unthinkable just a few years earlier. The population continued to grow, but food production increased even faster.
Every significant prediction also changes the behaviour of those who hear it and, in any case, is made within a complex context seeking equilibrium. If a bridge shows signs of structural failure, action is taken before it collapses. If a raw material becomes scarce, investment in the search for alternatives increases. If a disease appears dangerous, laboratories and health systems are mobilised. The most credible predictions often create the very conditions that may prevent them from coming true.
This is why it is useful to distinguish between a scenario and a prediction. A scenario describes what might happen if certain conditions remained unchanged. A prediction, by contrast, claims to describe what will actually happen.
The trouble is that scenarios are sometimes presented as predictions, or understood as predictions by those who lack sufficient intellectual tools. In complex systems, keeping this distinction in mind is essential, because conditions rarely remain unchanged.
There is also a psychological reason. People pay more attention to dangers than to reassurances. An absolute deadline, a countdown or a dramatic prediction inevitably attracts more attention than a cautious description full of uncertainties. Public communication therefore tends to favour the simplest and most clear-cut messages, while reality is almost always more nuanced.
Linear predictions remind us how difficult it is to imagine the future. But they also remind us of something more important: the ability of systems to adapt is an integral part of history.
To forget it is to watch only Giovannino’s growth, without realising that, sooner or later, he will stop growing.