Losing your job, having a lover ghost you, or seeing an important project collapse can feel like the end of the world. But as all-consuming as these experiences can be, they are personal catastrophes. CAE is concerned with endings in a broader sense.
So what do we mean by "the end of the world"?
Two categories are relevant to this question, each denoting a different level of catastrophe: existential and global.
Existential catastrophes
Likely the most widely-accepted definition of existential catastrophes comes from philosopher Nick Bostrom. Catastrophes deemed existential involve outcomes that would "annihilate Earth-originating intelligent life or permanently and drastically curtail its potential."
The first part of this definition is releatively straightforward. Humans--or whatever humans evolve into--go extinct. This may be due to an apocalyptic asteroid strike, a malevolent artifical intelligence, or the release of a deadly biological weapon. The result if the same: no more people.
The second part of Bostrom's definition is more complex and requires some unpacking. It assumes that humans have immense potential for scientific and technological advancement, and that this potential will ultimately allow us to become beings of immense, even incomprehensible power and knowledge. This may happen quickly through a Singularity-type event, or a more gradual process of guided evolution and innovation.
Any event that precludes our species reaching its potential--like a nuclear war that pushes humanity into a permanent dark age and prevents us from acheiving technological maturity--would, by this definition, qualify as an existential catastrophe.
Global catastrophes
Defining global catastrophes is a trickier proposition. Unlike existential catastrophes, which have a definitive meaning, assigning a threshold for what qualifies as a global catastrophe is a somewhat arbitrary affair. One report identifies global catastrophe as an "event or process that. . . would end the lives of approximately 10% or more of the global population, or do comparable damage." Some scholars set the percentage lower, but admit the definition is vague, and a precise threshold unnecessary. Others set the percentage significantly higher.
The words "comparable damage" introduce additional ambiguity. Some stipulate global financial losses of ten trillion dollars or more as constituting a globla catastrophe, but other thresholds might include massive and world-wide loss of infrastructure or other events that produce drastic and global transformation for human life and civilization.
Even as we acknowledge the imprecision and ambiguity of these thresholds, we can define global catastrophes thusly: any event or process that exhausts the resilience of human civilization, exceeding its capacity to weather disturbances and sustain its general conditions.
Defining the end of the world
Existential catastrophes are subcategories of global catastrophes. Either of these two constitute, in our definition, world-ending events. A global catastrophe would bring the end of the world "as we know it," that is to say, a radical transformation of human life. An existential catastrophe, on the other hand, would, at a minimum, permenently eliminate Earth-originating intelligent (i.e., human) existence or drastically curtail its potential, even though "the world," as it exists outside of human experience, might continue. More extreme existential catastrophes--e.g., a simulation shut-down or cosmic events like supernovae or gallactic collisions--may annihilate our planet, solar system, or even the universe itself.
With these definitions established, we can characterize the end of the world according to three variables: scope (the breadth of the effect), intensity (the severity of the effect), and time (the speed at which the event or process occurs). Using these variables, we can construct a diagram to establish a taxonomy for different types of events and processes.
In Figure A, an event that is personal, imperceptible, and instantaneous might be the loss of a single human hair. Global and endurable processes that take centuries to unfold might include the rise of average world temperatures by three degrees. A simulation shutdown would fall at the extreme near, top, and right of this fugure--universal, terminal, and instantaneous.
End of the world scenarios are shaded green. These areas denote events and processes that are relatively rapid, and within the spans of global to universal, and endurable to terminal.
Green is the goal. As should be evident from this figure, there is immense space for creative solutions, and many pathways to success. How we navigate to that space is up to us.