Social media platforms have witnessed a substantial increase in social bot activity, significantly affecting online discourse. Our study explores the dynamic nature of bot engagement related to Extinction Rebellion climate change protests from 18 November 2019 to 10 December 2019. We find that bots exert a greater influence on human behavior than vice versa during heated online periods. To assess the causal impact of human-bot communication, we compared communication histories between human users who directly interacted with bots and matched human users who did not. Our findings demonstrate a consistent negative impact of bot interactions on subsequent human sentiment, with exposed users displaying significantly more negative sentiment than their counterparts. Furthermore, the nature of bot interaction influences human tweeting activity and the sentiment towards protests. Political astroturfing bots increase activity, whereas other bots decrease it. Sentiment changes towards protests depend on the user's original support level, indicating targeted manipulation. However, bot interactions do not change activists' engagement towards protests. Despite the seemingly minor impact of individual bot encounters, the cumulative effect is profound due to the large volume of bot communication. Our findings underscore the importance of unrestricted access to social media data for studying the prevalence and influence of social bots, as with new technological advancements distinguishing between bots and humans becomes nearly impossible.

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