We present ideas about concepts underlying climate change, held by students in years 9 and 10. Misconceptions about climate change are common among students, and may be due to misconceptions about underlying concepts. To investigate this, we developed the Climate Change Concept Inventory (CCCI), and trialed it with 229 students; corroborating findings through focus group interviews. Our interview method and data analysis methods are described. Findings included overestimation of human contributions to atmospheric carbon inputs, ultra violet radiation in sunlight, and greenhouse gases in the atmosphere. Students were unaware that CO2 dissolves in water, and of the role of oceans in the carbon cycle. Greenhouse gases other than CO2 were rarely known. Earth's energy balance and black body radiation were not well understood. There were misconceptions about interactions between electromagnetic radiation and atmospheric gases; and limited understanding of carbon chemistry. The CCCI is available from the corresponding author.