<p>This study examines the differentiated effects of optimism and pessimism on climate action intentions and self-reported climate action using large-scale survey data from 1552 adult participants in South Korea. The findings show that the effects of optimism and pessimism vary depending on whether they are conceptualized as general dispositions or as climate change–specific evaluations, as well as on whether intentions or behavior are considered. At the dispositional level, general optimism was positively associated with both climate action intentions and self-reported climate action, whereas general pessimism showed no significant relationship with either outcome. This suggests that dispositional optimism functions as a broad motivational resource supporting engagement across both stages. In contrast, climate change–specific optimism was positively associated with climate action intentions but not with self-reported behavior, indicating a potential intention–behavior gap. Climate change–specific pessimism was unrelated to intentions but showed a modest positive association with self-reported climate action. Taken together, these results underscore the importance of analytically distinguishing between dispositions and issue-specific evaluations, as well as between intentions and behavior. They also suggest that optimism and pessimism may play differentiated roles across stages of climate engagement, offering insights relevant for future research on climate communication and behavioral responses under conditions of uncertainty.</p>