There may be cases where people collectively cause a morally significant outcome, but no individual act seems to make a difference, or at least enough of a difference to give them sufficient reason not to act as they do. Climate change is often portrayed as a case of this sort—a collective action problem of the grandest scale. The idea is that, holding what others do fixed, no individual agent has very weighty reason to reduce emissions, since any such behavioural change would not yield sufficient expected harm reduction to outweigh the costs to the agent. Consequently, no one of these individuals is accountable for the harms resulting from climate change (Kingston and Sinnot-Armstrong 2018). And yet the tragedy is that the simultaneous emissions reduction of many agents, yielding a large aggregate harm reduction, would easily warrant the costs borne by each of them to achieve this aim.