The argument has been made that future generations of human beings are being harmed unjustifiably by the actions individuals commit today. This paper addresses what it might mean to harm future generations, whether we might harm them, and what our duties toward future generations might be. After introducing the Global Health Impact (GHI) concept as a unit of measurement that evaluates the effects of human actions on the health of all organisms, an incomplete theory of human justice is proposed. Having (...) shown that the negative GHIs of our current generation cause unfair harm to future generations, I argue that each human being must be allocated a fair threshold of negative GHIs that should not be exceeded. By emphasising the need to consider all the GHIs of human actions, the theory of human justice developed here is highly relevant to evaluate human actions that might affect future generations, for example those related to climate change. (shrink)