Some terms and concepts that are important to many longtermists are existential risk, extinction risk, global catastrophic risk, and suffering risk. Also important are the terms and concepts for the four types of catastrophes corresponding to those four types of risks.^[1]

Unfortunately, people sometimes mistakenly use one of these terms as if synonymous for another of these terms, or mistakenly present one concept as entirely fitting as a subset of another. Other times, people discuss these concepts in complete isolation from each other, which is not a mistake, but may sometimes be a missed opportunity.

In reality, there are important distinctions and important overlaps between these terms and concepts. So this post reviews definitions and descriptions of those four types of catastrophes, discusses how they relate to each other, and presents three Venn diagrams (which include example scenarios) to summarise these points. I hope this can help increase the conceptual clarity of discussions and thinking regarding longtermism and/or large-scale risks.

This post primarily summarises and analyzes existing ideas, rather than presenting novel ideas.

Existential catastrophe, extinction, and failed continuation

In The Precipice, Toby Ord defines an existential catastrophe as “the destruction of humanity’s longterm potential.”^[2] Extinction is one way humanity’s long-term potential could be destroyed,^[3] but not the only way. Ord gives the following breakdown of different types of existential catastrophe:

(For those interested, I’ve previously collected links to works on collapse and on dystopia.)

We could thus represent the relationship between the concepts of existential catastrophe, extinction, and failed continuation via the following Venn diagram:^[4]

I’ve included in that Venn diagram some example scenarios. Note that:

• All of the example scenarios used in this post really are just examples; there are many other scenarios that could fit within each category, and some may be more likely than the scenarios I’ve shown.
• Whether a scenario really counts as an existential catastrophe depends on one’s moral theory or values (or the “correct” moral theory of values), because that affects what counts as fulfilling or destroying humanity’s long-term potential.
• The sizes of each section of each Venn diagram are not meant to reflect relative likelihoods. E.g., I don’t mean to imply that extinction and failed continuation are exactly as likely as each other.

Global and existential catastrophes

Multiple definitions of global catastrophic risks have been proposed, some of which differ substantially. I’ll use the loose definition provided by Bostrom & Ćirković (2008, p.1-2) in the book Global Catastrophic Risks:

The term 'global catastrophic risk' lacks a sharp definition. We use it to refer, loosely, to a risk that might have the potential to inflict serious damage to human well-being on a global scale.

[...] a catastrophe that caused 10,000 fatalities or 10 billion dollars worth of economic damage (e.g., a major earthquake) would not qualify as a global catastrophe. A catastrophe that caused 10 million fatalities or 10 trillion dollars worth of economic loss (e.g., an influenza pandemic) would count as a global catastrophe, even if some region of the world escaped unscathed. As for disasters falling between these points, the definition is vague. The stipulation of a precise cut-off does not appear needful at this stage. [emphasis added]

Given this definition, many existential catastrophes would also be global catastrophes. This includes all potential extinction events, many or all potential unrecoverable collapse events, and many potential transitions to unrecoverable dystopia. However, the terms “existential catastrophe” and “global catastrophe” are not synonymous, for two reasons.

Firstly, a wide array of global catastrophes would not be existential catastrophes. Indeed, “global catastrophe” is a notably “lower bar”, and so global catastrophes may be much more likely than existential catastrophes. (See also Database of existential risk estimates.)

Secondly, some existential catastrophes wouldn’t be global catastrophes (given Bostrom & Ćirković’s definition), because they wouldn’t involve any sudden spike in deaths or economic damage. This applies most clearly to “desired dystopias”, in which a large portion of the people at the time actually favour the outcomes that occur (e.g., due to sharing a deeply flawed ideology). A desired dystopia may therefore not be recognised as a catastrophe by anyone who experiences it.^[5] Ord’s (2020) “plausible examples” of a desired dystopia include:

worlds that forever fail to recognise some key form of harm or injustice (and thus perpetuate it blindly), worlds that lock in a single fundamentalist religion, and worlds where we deliberately replace ourselves with something that we didn’t realise was much less valuable (such as machines incapable of feeling).

It’s also possible that some transitions to undesired or enforced dystopias (e.g., totalitarian regimes) could occur with no (or little) bloodshed or economic damage.^[6]

In contrast, unrecoverable collapse seems likely to involve a large number of deaths. It also seems to almost “by definition” involve major economic damage. And extinction would of course involve a huge amount of death and economic damage.

We could thus represent the relationship between the concepts of global catastrophe, existential catastrophe, extinction, and failed continuation via the following Venn diagram:

Suffering, existential, and global catastrophes

Suffering risks (also known as risks of astronomical suffering, or s-risks) are typically defined as “risks where an adverse outcome would bring about suffering on an astronomical scale, vastly exceeding all suffering that has existed on Earth so far” (Daniel, 2017).^[7] (Update in 2022: That source has been updated to give the following definition instead: "S-risks are risks of events that bring about suffering in cosmically significant amounts. By “significant”, we mean significant relative to expected future suffering." This definition does seem better to me, for the reasons that Lukas Gloor mentions in a comment.)

I’ll use the term suffering catastrophe to describe the realisation of an s-risk; i.e., an event or process involving suffering on an astronomical scale.^[8]

Two mistakes people sometimes make are discussing s-risks as if they’re entirely distinct from existential risks, or discussing s-risks as if they’re a subset of existential risks. In reality:

1. There are substantial overlaps between suffering catastrophes and existential catastrophes, because some existential catastrophes would involve or result in suffering on an astronomical scale.

   • Most obviously, many unrecoverable dystopia scenarios would involve suffering of humans or nonhumans on an astronomical scale. For example, a stable, global totalitarian regime could cause many billions of humans to suffer in slavery-like conditions each generation, for many generations (see also Reducing long-term risks from malevolent actors). Or a “desired dystopia” might involve huge numbers of suffering wild animals (via terraforming) or suffering digital minds, because humanity fails to realise that that’s problematic.
   • As another example, some AI-induced extinction events may be followed by large amounts of suffering, such as if the AI then runs huge numbers of highly detailed simulations including sentient beings (see e.g. Tomasik).^[9]

2. But there could also be suffering catastrophes that aren’t existential catastrophes, because they don’t involve the destruction of (the vast majority of) humanity’s long-term potential.

   • This depends on one’s moral theory or values (or the “correct” moral theory or values), because, as noted above, that affects what counts as fulfilling or destroying humanity’s long-term potential.
   • For example, the Center on Long-Term Risk notes: “Depending on how you understand the [idea of loss of “potential” in definitions] of [existential risks], there actually may be s-risks which aren’t [existential risks]. This would be true if you think that reaching the full potential of Earth-originating intelligent life could involve suffering on an astronomical scale, i.e., the realisation of an s-risk. Think of a quarter of the universe filled with suffering, and three quarters filled with happiness. Considering such an outcome to be the full potential of humanity seems to require the view that the suffering involved would be outweighed by other, desirable features of reaching this full potential, such as vast amounts of happiness.”
   • In contrast, given a sufficiently suffering-focused theory of ethics, anything other than near-complete eradication of suffering might count as an existential catastrophe.

Likewise:

1. There are substantial overlaps between suffering catastrophes and global catastrophes, because some suffering catastrophes (or the events that cause them) would involve major human fatalities and economic damage.

2. But there could also be suffering catastrophes that aren’t global catastrophes, because they don’t involve major human fatalities and economic damage.

   • In particular, there could be suffering among nonhumans and/or ongoing human suffering without a spike in human fatalities at any particular time.

We could thus represent the relationship between the concepts of suffering catastrophe, existential catastrophe, and global catastrophe via the following Venn diagram (although this diagram might be inaccurate, given a sufficiently suffering-focused theory of ethics):

If you found this post interesting, you may also find interesting my previous posts Clarifying existential risks and existential catastrophes and 3 suggestions about jargon in EA.

I’m grateful to Tobias Baumann, Anthony D, and David Kristoffersson for helpful feedback. I’m also grateful to David for discussions that may have informed the ideas I expressed in this post. This does not imply these people's endorsement of all of this post’s claims.

I wrote this post in my personal time, and it doesn’t necessarily represent the views of any of my employers.