How and When Incivility Unfolds in Online Heatwave Communication: Characterizing Public Discussions on Reddit

The increasing frequency of heatwaves has sparked widespread concern and emotionally charged, often uncivil, discussions on social media. Drawing on heatwave communication and online incivility research, this study investigates the patterns and antecedents of incivility in Reddit threads from 2023 to 2024 about heatwaves. Specifically, it examines how incivility unfolds across comment threads and how emotional expressions and topics shape uncivil comments. Using natural language processing (i.e., topic modelling and emotion analysis) as well as a large language model-assisted incivility detection approach, we analyzed 1,369 posts, 10,800 firstlayer comments, and 7,297 second-layer comments from eight climate-and country-related subreddits. Results revealed incivility was more prevalent in comments than posts, with firstlayer incivility significantly predicting second-layer instances, hinting at a contagion effect that intensified in deeper threads. Comments expressing anger, disgust, sadness, or surprise were more likely to be uncivil, and controversial topics like climate change attribution, geopolitical conflicts, and regional impacts strongly correlated with higher incivility. Theoretical and practical implications were discussed.