Science activism is often seen as a threat to scientific credibility. Yet, an increasing number of scientists participate in climate activism and challenge the morality of remaining passive when urgent action is needed. Science activism for climate action (SACA) raises intriguing questions about the source of scientific credibility and the boundaries of a scientist's professional role responsibility. This contribution informs discussions over (the appropriateness of) SACA by explicating different conceptualizations of this phenomenon. Arguments for SACA are used to formulate three conceptual configurations that assume different relations between the role of the scientist and the role of the activist: the scientist activist as a citizen; the scientist activist as a privileged citizen; the scientist activist as a professional. To better situate these configurations, we consider the perspectives of scientists with a direct or indirect involvement in climate action. Secondary sources of empirical nature (interviews with scientist activists; proceedings of a workshop with early-career researchers) enrich our analysis with the practitioners' reasoning over science activism, its relation to their profession, and its relation to scientific credibility. Eventually, we reflect on the implications of each configuration for the embedding of science activism in scientific conduct.