Education must provide substantive knowledge, skills, attitudes, and behaviors toward environmental education. This study aims to identify seventh-grade students' conceptions regarding climate change, global warming, and the greenhouse effect. The research was conducted at four local secondary schools in the Special Region of Yogyakarta, Indonesia. Data were gathered through open-ended questionnaires to 140 students, which were analyzed inductively to identify concepts and patterns. The result indicated that students believe that five harmful environmental behaviors cause global warming: (1) use of fossil fuels; (2) deforestation; (3) use of aerosols; (4) littering; and (5) air pollution. The five activities produce the greenhouse effect and deplete the ozone layer, which causes global warming. Global warming has an adverse impact on the earth's ocean, soil, air, plants and animals, humans, weather, and season changes. The students' thoughts were substantially linear and simplified: human activities cause global warming, impacting individuals through health risks, food preservation, and conservation. Appropriate human actions would reduce greenhouse gases (GHGs) and global warming, thereby decreasing ecological problems. This research is expected to enhance and guide the effective implementation of environmental education concerning climate change issues because students' conceptions and actions are crucial for sustainability.