Climate negotiation outcomes are difficult to evaluate objectively because there are no clear reference scenarios. Subjective assessments from those directly involved in the negotiations are particularly important, as this may influence strategy and future negotiation participation. Here we analyse the perceived success of the climate negotiations in a sample of 656 experts involved in international climate policy. Respondents were pessimistic when asked for specific assessments of the current approach centred on voluntary pledges, but were more optimistic when asked for general assessments of the outcomes and usefulness of the climate negotiations. Individuals who were more involved in the negotiation process tended to be more optimistic, especially in terms of general assessments. Our results indicate that two reinforcing effects are at work: a high degree of involvement changes individuals’ perceptions and more optimistic individuals are more inclined to remain involved in the negotiations.