An experimental system for detecting infrared absorption using the photoacoustic (PA) effect is described. It is aimed for use at high-school level to illustrate the difference in infrared (IR) absorption among the gases contained in the atmosphere in connection with the greenhouse effect. The experimental system can be built with readily available components and is suitable for small-group experiments. The PA signal from a greenhouse gas (GHG), such as CO[subscript 2], H[subscript 2]O, and CH[subscript 4], can be detected down to a concentration of 0.1%. Since the basic theory of the PA effect in gases due to IR absorption is straightforward, the experiments with this PA system are accessible to students. It can be shown that there is a significant difference in IR absorption between GHGs and the major components of the atmosphere, N[subscript 2], O[subscript 2], and Ar, which helps students understand that the minor components, that is, the GHGs, determine the IR absorptivity of the atmosphere. (Contains 4 figures.)