This post is the first part of my summary of The Precipice, by Toby Ord. It is about what existential risks are, and it explores the natural sources of existential risks. Future posts will explore the danger from other sources, our place in the story of humanity, and the importance of reducing existential risk.

What is an existential risk?

An existential catastrophe is any event that would destroy humanity’s potential. This could take a few forms:^[1]

Ordinary extinction: Every human on Earth dies, or there are too few survivors to repopulate it.
Permanent civilisational collapse: An enormous catastrophe collapses civilisation and severely damages the environment in a way that makes it impossible to rebuild. This would be a world without writing, cities, and law. A collapse of civilisation might or might not be an existential catastrophe; it depends on whether we can rebuild.
A world in chains: The entire world is locked under totalitarian rule. Advanced technology allows permanent and powerful indoctrination, surveillance, and enforcement, leaving no chance for an uprising and no internal or external pressure to change. Like civilisational collapse, this presents an existential catastrophe if the situation is permanent.

How can we estimate the danger?

One way is to assume the risk is negligible until there is strong scientific evidence determining that it is higher. This ensures that risks are not exaggerated but does not usually reflect our current understanding of the risks and might lead to dangerous underestimation of emerging risks.^[2] Instead, Toby Ord begins with an initial impression of the size of the risk, then adjusts this estimate according to the scientific evidence.

The sources of natural extinction risk

Asteroids and comets

Sixty-six million years ago an asteroid hit Earth off the coast of Mexico, burning everything within 1,000 kilometres. The worst effects were caused by a billowing cloud of dust and ash (and sulphate aerosols from the vaporised sea floor) which blocked out the sun and cooled Earth. In the end, every land vertebrate over five kilograms went extinct (Longrich, Scriberas and Wills, 2016).

Supervolcanic eruptions

The very largest volcanic eruptions don’t look like typical volcanoes. Instead of mountains spilling out molten rock, supervolcanoes collapse into a vast craterlike depression (a well-known exam...

Book Summary: The Precipice