Hi everyone! Below is a summary of the chapter that Maya Eden and I wrote for Essays on Longtermism.
What socially beneficial causes should altruists prioritize if they give equal ethical weight to the welfare of current and future generations? Many have argued that, because human extinction would result in a permanent loss of all future generations, extinction risk mitigation should be the top priority. We call this the long-run argument for extinction risk mitigation.
In Alexandrie and Eden (2025), we evaluate the long-run argument for extinction risk mitigation through the lens of population models. Below we outline what we take to be the two key takeaways of the paper.
Takeaway 1: The long-run argument for extinction risk mitigation relies on the assumption that the global population would partly recover after a non-extinction catastrophe We present a theoretical framework for quantifying the cost-effectiveness of interventions aimed at preventing negative shocks to the size of the global population. A heuristic implied by this framework is that the undiscounted cost-effectiveness of reducing the risk of a negative population shock is proportional to the ratio of future lives lost (in percentage terms) to current lives lost (in percentage terms). We call this the long-term value ratio.
Let us compare the cost-effectiveness of reducing extinction risk with that of reducing the risk of a catastrophe that would kill 10% of the population. Since human extinction would result in a loss of 100% of current lives and 100% of future lives, the long-term value ratio of extinction risk mitigation is 1. Now, a catastrophe that would kill 10% of current lives may result in a loss of less than 10% of future lives (if there is recovery) and more than 10% of future lives (if there is amplification). Therefore, if there is recovery, the long-term value ratio of mitigating the 10%-catastrophe is higher than 1; if there is amplification, it is less than 1. This example shows that (partial) recovery is necessary for extinction risk mitigation to be more cost-effective than other types of catastrophic risk mitigation.
Takeaway 2: Population models suggest that nothing guarantees recovery after a negative population shock We distinguish between two different negative shocks to the size of the global population. A pure population shock is an event that kills some fraction of the world population without having much direct impact on other factors of production (e.g., a pandemic that kills people, but doesn’t destroy physical capital). An all-factor shock is an event that destroys all factors of production in equal proportion (e.g., an asteroid that kills the same fraction of people as it destroys physical capital).
Pure population shocks and all-factor shocks have different implications for recovery dynamics after the shock. We consider three models of such fertility dynamics: the social determinants model, the Barro-Becker model, and the Malthusian model. For pure population shocks, only the Malthusian model unambiguously implies that the population would recover after a shock. For all-factor shocks, none of the models imply that such recovery would occur, at least if natural resources are destroyed in the same proportion as population and physical capital. This is because the population models we consider imply that the economic determinants of fertility are invariant to the scale of the economy, which is all that is affected by all-factor shocks.
Conclusion The long-run argument for prioritizing extinction risk mitigation relies on the assumption that the global population would partly recover after a non-extinction catastrophe (Takeaway 1). However, population models suggest that nothing guarantees that such recovery would occur after a non-extinction catastrophe (Takeaway 2). Together, these two takeaways provide a challenge to the long-run argument for prioritizing extinction risk mitigation.
Hi everyone! Below is a summary of the chapter that Maya Eden and I wrote for Essays on Longtermism.
What socially beneficial causes should altruists prioritize if they give equal ethical weight to the welfare of current and future generations? Many have argued that, because human extinction would result in a permanent loss of all future generations, extinction risk mitigation should be the top priority. We call this the long-run argument for extinction risk mitigation.
In Alexandrie and Eden (2025), we evaluate the long-run argument for extinction risk mitigation through the lens of population models. Below we outline what we take to be the two key takeaways of the paper.
Takeaway 1: The long-run argument for extinction risk mitigation relies on the assumption that the global population would partly recover after a non-extinction catastrophe
We present a theoretical framework for quantifying the cost-effectiveness of interventions aimed at preventing negative shocks to the size of the global population. A heuristic implied by this framework is that the undiscounted cost-effectiveness of reducing the risk of a negative population shock is proportional to the ratio of future lives lost (in percentage terms) to current lives lost (in percentage terms). We call this the long-term value ratio.
Let us compare the cost-effectiveness of reducing extinction risk with that of reducing the risk of a catastrophe that would kill 10% of the population. Since human extinction would result in a loss of 100% of current lives and 100% of future lives, the long-term value ratio of extinction risk mitigation is 1. Now, a catastrophe that would kill 10% of current lives may result in a loss of less than 10% of future lives (if there is recovery) and more than 10% of future lives (if there is amplification). Therefore, if there is recovery, the long-term value ratio of mitigating the 10%-catastrophe is higher than 1; if there is amplification, it is less than 1. This example shows that (partial) recovery is necessary for extinction risk mitigation to be more cost-effective than other types of catastrophic risk mitigation.
Takeaway 2: Population models suggest that nothing guarantees recovery after a negative population shock
We distinguish between two different negative shocks to the size of the global population. A pure population shock is an event that kills some fraction of the world population without having much direct impact on other factors of production (e.g., a pandemic that kills people, but doesn’t destroy physical capital). An all-factor shock is an event that destroys all factors of production in equal proportion (e.g., an asteroid that kills the same fraction of people as it destroys physical capital).
Pure population shocks and all-factor shocks have different implications for recovery dynamics after the shock. We consider three models of such fertility dynamics: the social determinants model, the Barro-Becker model, and the Malthusian model. For pure population shocks, only the Malthusian model unambiguously implies that the population would recover after a shock. For all-factor shocks, none of the models imply that such recovery would occur, at least if natural resources are destroyed in the same proportion as population and physical capital. This is because the population models we consider imply that the economic determinants of fertility are invariant to the scale of the economy, which is all that is affected by all-factor shocks.
Conclusion
The long-run argument for prioritizing extinction risk mitigation relies on the assumption that the global population would partly recover after a non-extinction catastrophe (Takeaway 1). However, population models suggest that nothing guarantees that such recovery would occur after a non-extinction catastrophe (Takeaway 2). Together, these two takeaways provide a challenge to the long-run argument for prioritizing extinction risk mitigation.