Timing uncertainty in collective risk dilemmas encourages group reciprocation and polarization

<p><span><span><span><span><span><span><span><span><span><span><span>Social dilemmas are often shaped by actions involving uncertain returns only achievable in the future, such as climate action or voluntary vaccination. In this context, uncertainty may produce non-trivial effects. Here, we assess experimentally — through a collective risk dilemma — the effect of timing uncertainty, i.e. how uncertainty about when a target needs to be reached affects the participants' behaviours. We show that timing uncertainty prompts not only early generosity but also polarised outcomes, where participants' total contributions are distributed unevenly. Furthermore, analysing participants' behaviour under timing uncertainty reveals an increase in reciprocal strategies. A data-driven game-theoretical model captures the self-organizing dynamics underpinning these behavioural patterns. Timing uncertainty thus casts a shadow on the future that leads participants to respond early, while reciprocal strategies appear to be important for group success. Yet, the same uncertainty also leads to inequity and polarisation, necessitating the inclusion of new incentives handling these societal issues. </span></span></span></span></span></span></span></span></span></span></span></p>