As contemporary ethical discourse has highlighted, due to the world’s increasing connectedness, everyday actions can contribute to harmful consequences far removed from everyday experience. I argue that Aquinas’s treatment of consequences can give us insight into our responsibility for such effects of our actions on a global scale. In particular, Aquinas recognises that we are responsible for per accidens effects of good actions performed negligently. Even an unintended per accidens effect may follow with a degree of likelihood that makes it foreseeable, even if not actually foreseen; thus the agent is responsible if he fails to take steps to prevent the negative per accidens effect from occurring. I argue that certain global effects of our actions fit this pattern, namely, they are per accidens effects that nonetheless follow from our actions with a high degree of likelihood. Thus, we have a responsibility to take steps to prevent them.