Trends in Atmospheric Carbon Dioxide is one of a series of Data Point resources from HHMI Biointeractive. Data Points engage students in analyzing and interpreting data from primary literature in the biological sciences. The resources provide authentic phenomena to spark student discussion and exploration. Alternatively they can serve as three-dimensional assessment items or review if the discussion prompt is used after students have learned the concepts. This resource engages students in analyzing and interpreting data from a primary source, and the teacher guide provides a link to that source (https://scripps.ucsd.edu/programs/keelingcurve/).