This paper argues the relevance of the internet for scientific communication. It is not only an immense source of information, it also empowers laypeople to interact by commenting, rating, and sharing online content. Previous studies have found that users' contributions to online content affect the reception processes. However, research on who actually uses these participatory possibilities is scarce. This paper characterizes engaged (and non-engaged) online users by analyzing online engagement (using search engines and different participatory forms) with a representative German online survey (n = 1,463). Different groups of climate change perceptions (such as uncertainty of scientific evidence), attitudes, knowledge, and online engagement are identified with hierarchical cluster analyses. Interest and knowledge are main drivers of online engagement, although a group of uninterested, unknowing and doubtful users participates in SNSs. The most active group, participating experts, knows most about scientific processes in climate sciences. No distinct group of skeptical participants was identified.