Population ethics is the philosophical study of the ethical problems concerning populations. It is also sometimes called population axiology, which is "the theory of when one state of affairs is better than another, where the states of affairs may differ over the number of people who ever live". It deals with the special problems that arise when actions or policies cannot be said to affect individual persons but merely to substitute one group of people with another. Such problems usually only arise when our actions affect future generations.
“Most discussion in population ethics has concentrated on how to evaluate populations in regard to their goodness, that is, how to order populations by the relations “is better than” and “is as good as”. This field has been riddled with paradoxes which purport to show that our considered beliefs are inconsistent in cases where the number of people and their welfare varies.”
Population ethics is especially important when making large-scale decisions like those regarding climate policy.