Little research is evident about integration of mathematics in sustainability tasks to raise students' awareness and actions to solve a sustainability challenge. In this paper, we explore how a teacher designed and implemented a sustainability project, which included mathematics to raise Year 10 students' (aged 15-16) awareness and actions about sustainability. Data, including classroom observations and interviews, were analysed based on one characteristic of the green mathematics framework: "projection." We report on how students used mathematics to project future situations and how the projection may raise students' awareness and actions to address sustainability.