Students often find it difficult to apply critical thinking skills across multiple representations of data. Flux-and-pool diagrams of the global carbon cycle and graphs of atmospheric CO2 levels are two important representations that students need to be able to use to understand global climate change scenarios. Students should be able to (a) interpret both the diagram and the graph, (b) use the diagram to explain the graph, and (c) use the diagram to make projections about the effects of human actions that change fluxes. In this poster, we share a learning progression framework for interpreting undergraduate students’ ability to use these representations. The data show that without specific interventions, undergraduates are likely to conflate changes in flux rates such as a reduction in people’s use of fossil fuels with pool size. This misconception makes the environmental problem seem more tractable than it really is.