Learning molecular behaviour may improve student explanatory models of the greenhouse effect

We assessed undergraduates’ representations of the greenhouse effect, based on student-generated concept sketches, before and after a 30-min constructivist lesson. Principal component analysis of features in student sketches revealed seven distinct and coherent explanatory models including a new Molecular Details model. After the lesson, which described the invisible molecular behaviour of gases, this group (n = 164) produced significantly more expert-like representations of the greenhouse effect, and included fewer novice ideas. The key behaviour that greenhouse gases emit radiation in random directions is new to most students and directly counters common explanations involving reflection and ‘trapping’ of radiation in the atmosphere. Thus, learning molecular behaviour of greenhouse gases may help students replace non-expert explanatory models. This Molecular Details model has not been previously identified, and is unlikely to have emerged from human evaluation of student sketches alone. When teaching the greenhouse effect, we propose that interventions explicitly incorporate greenhouse gas behaviour.