In US school settings and materials, climate change is often framed as an uncertain phenomenon. However, the effect of such denialist representations on youth's perceptions of climate change has not been empirically tested. To address this gap in the literature, this article reports on a survey-based experiment testing two framings of uncertainty about the causes and effects of climate change--one with a high level of uncertainty and one with a low level of uncertainty--on students' knowledge, attitudes, and behaviours related to climate change. The experiment was conducted with 453 middle and high school students. Students who read a text portraying climate change with high uncertainty reported lower levels of certainty about human-caused climate change. To explore how the students engaged cognitive resources when reading the experimental texts, regression analyses were used to test two hypotheses. The Knowledge Thesis predicts that youth will use their prior knowledge to evaluate the text, and the Norms Thesis predicts that youth will use the perceived norms of their social group to evaluate the text. Results suggested that students did not respond to the treatment differentially, given their differing levels of prior knowledge nor social norms accepting of climate change. Implications for practice include the necessity of explicit scaffolds to support deep critical engagement with informational, or dis-informational, text about climate change.