Standard economic theory assumes that individuals ignore the externalities they create, such as emissions from burning fossil fuels and generating waste. In an incentivized study (N=3,718), we find that most people forgo substantial gains to avoid imposing negative externalities on others. Using administrative data on household waste, we show a clear link between such prosociality and waste behavior: prosociality predicts lower residual waste generation and higher waste sorting. Prosociality also predicts survey-reported pro-environmental behaviors such as lowering indoor temperature, limiting air travel, and consuming eco-friendly products. These findings suggest that the impact of environmental policies depend on the population's prosociality.
