We present GreenHat, an interactive mobile learning application that helps students learn about biodiversity and sustainability issues in their surroundings from experts’ points of view, before participating in unfamiliar debates about their familiar surroundings. Using the interactive location-sensitive map and video on a smart phone, GreenHat simulates how experts go about making observations in the field and encourages students to actively observe their environment. We present our design process, our initial prototype, report the results from our preliminary evaluation, and discuss ongoing work. Keywords Mobile learning, sustainability, biodiversity, location-based information, expert perspectives