International climate negotiations have been troubled by mutual mistrust. At the same time, a hope seems to prevail that once enough countries moved forward, others would follow suit. If the abatement game faced by climate negotiators is a Prisoners' Dilemma, and countries are narrowly self-interested, such a hope seems unfounded. However, if countries display reciprocity – a preference to repay meanness by meanness and kindness by kindness – their willingness to abate will be conditional on others' abatement. I show that a full or majority coalition can be stable. This requires, however, that a majority of countries have relatively strong reciprocity preferences. No coalition participation is always stable. In addition, a stable minority coalition may exist; if so, it is weakly larger than the maximum stable coalition with standard preferences, but is characterized by mutually negative sentiments.