Early Science and Technology Studies (STS) scholars recognized that the social construction of knowledge depends on skepticism’s parasitic relationship to background expectations and trust. Subsequent generations have paid less empirical attention to skepticism in science and its relationship with trust. I seek to rehabilitate skepticism in STS – particularly, Merton’s view of skepticism as a scientific norm sustained by trust among status peers – with a study of what I call ‘civil skepticism’. The empirical grounding is a case in contemporary dendroclimatology and the development of a method (‘Blue Intensity’) for generating knowledge about climate change from trees. I present a sequence of four instances of civil skepticism involved in making Blue Intensity more resistant to critique, and hence credible (in laboratory experiments, workshops, conferences, and peer-review of articles). These skeptical interactions depended upon maintaining communal notions of civility among an increasingly extended network of mutually trusted peers through a variety of means: by making Blue Intensity complementary to existing methods used to study a diverse natural world (tree-ring patterns) and by contributing to a shared professional goal (the study of global climate change). I conclude with a sociological theory about the role of civil skepticism in constituting knowledge-claims of greater generality and relevance.