There are a number of cases where, collectively, groups cause harm, and yet no single individual’s contribution to the collective makes any difference to the amount of harm that is caused. For instance, though human activity is collectively causing climate change, my individual greenhouse gas emissions are neither necessary nor sufficient for any harm that results from climate change. Some (e.g., Sinnott-Armstrong) take this to indicate that there is no individual moral obligation to reduce emissions. There is a collective action problem here, to which I offer a solution. My solution rests on an argument for a (sometimes) bare moral difference between intending harm and foreseeing with near certainty that harm will result as an unintended side-effect of one’s action. I conclude that we have a moral obligation to reduce our individual emissions, and, more broadly, an obligation to not participate in many other harmful group activities (e.g., factory-farming).