This passage in Derek Parfit’s Reasons and Persons (1984) deserves calling out, not least because it sets the stage for the arguments against climate change despair I reviewed in a previous post.

In small communities, it is a plausible claim that we cannot have harmed others if there is no one with an obvious complaint, or ground for resenting what we have done.

Until this century, most of mankind lived in small communities. What each did could affect only a few others. But conditions have now changed. Each of us can now, in countless ways, affect countless other people. We can have real though small effects on thousands or millions of people. When these effects are widely dispersed, they may be either trivial, or imperceptible. It now makes a great difference whether we continue to believe that we cannot have greatly harmed or benefited others unless there are people with obvious grounds for resentment or gratitude. While we continue to believe this, even if we care about effects on others, we may fail to solve many serious Prisoner’s Dilemmas. For the sake of small benefits to ourselves, or our families, each of us may deny others much greater total benefits, or impose on others much greater total harms. We may think this permissible because the effects on the others will either be trivial or imperceptible. If this is what we think, what we do will often be much worse for all of us.

If we cared sufficiently about effects on others, and changed our moral view, we would solve such problems. It is not enough to ask, ‘Will my act harm other people?’ Even if the answer is No, my act may still be wrong, because of its effects. The effects that it will have when it is considered on its own may not be its only relevant effects. I should ask, ‘Will my act be one of a set of acts that will together harm other people?’ The answer may be Yes. And the harm to others may be great. If this is so, I may be acting very wrongly…. We must accept this view if our concern for others is to yield solutions to most of the many Prisoner’s Dilemmas that we face: most of the many cases where, if each of us rather than none of us does what will be better for himself — or for his family, or those he loves — this will be worse, and often much worse, for everyone.