As part of a large-scale instructional intervention research, this study examined elementary students' science knowledge and awareness of social activism with regard to an increased greenhouse effect and global warming. The study involved fifth-grade students from five elementary schools of varying demographic makeup in a large urban school district in the United States. The study was based on the analysis of students' responses to a writing prompt addressing an increased greenhouse effect and global warming at the beginning of and at the completion of instruction over the school year. The results indicate that students with adequate science knowledge tended to express activism more frequently, and that their expression of activism increased as they gained better science knowledge after the instruction. The results highlight the importance of effective instruction of this contemporary and controversial issue with K-12 students, so that they come to be aware of this societal problem, take action in solving the problem, and become socially responsible youth and adults.