The fat tail

First published in Idea Festival’s blog.

In the long list of maladies plaguing humanity, climate change stands out in many ways. If unmitigated, it is likely to cause suffering and devastation at scales beyond our imagination.

Climate change is probably the most global of all challenges. The long timescales, measured in centuries and millennia, are difficult for people to grasp. The scientific complexity of the phenomenon is mind-boggling.

But one reason makes climate change even more unique. It is the fat tail.

The possible impacts of climate change can be approximated with a bell curve. The y axis gives us the probability of a given impact level. The x axis describes the magnitude of impacts, increasing from left to right.

What does the climate impact curve look like? There is a small probability that the impacts remain moderate. The most likely outcome – the big bulge in the middle of the curve – is destruction ranging from considerable to massive.

The fat tail is at the other end of the curve. The tail illustrates the low-probability high-impact scenarios: drastic warming crossing the upper boundaries in the most quoted estimates, climate change spiralling out of control.

The probability for impacts this extreme is indeed very small. Worryingly enough it is still greater than zero.

If all this sounds too sciencey, there is a simpler way of putting it: there is a tiny chance that climate change will end civilisation as we know it. That is the fat tail that makes climate change different.

Oras Tynkkynen

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