Hundreds of thousands of undergraduates enroll in general education science courses to fulfill university core requirements. However, many of these lecture-based courses fail to foster high-level data literacy skills. This work details the design, implementation, and analysis of a new climate change-based classroom activity for college students that pairs data interpretation with participation in an online citizen science project called Floating Forests (http://floatingforests.org). We pilot tested our activity in introductory geoscience and biology courses at six universities ([approximately] 1,500 students) during the 2020-2021 academic year. Additionally, we developed and validated a survey to assess how engagement with our activity impacted students' self-reported changes across four factors: (1) perceptions of the impacts of climate change, (2) data literacy self-efficacy, (3) beliefs about the value of citizen science, and (4) beliefs about science engagement. In a pre- to post-test comparison, students who utilized our activity in their courses showed statistically significant increases (p < 0.05) across all four factors. These results highlight the potential benefit of implementing data-driven, citizen science-based activities in introductory-level undergraduate courses.