If climate scientists still doesn't understand basic chemistry.
See pic related from NOAA official site. They say it is "concentrations" but "concentrations" as defined by old school chemistry book such as Lewis and Randall "Advanced Thermodynamics" (1962) refer to unit of mol/volume. PPM on the other hand refer to mol species/mol air in the atmosphere, or mol species/mol water in ocean measurements. I'm not saying the basis of climate change is incorrect, I'm just annoyed by the wrong use of units. Pic related should be labeled "CO2 mole fraction" rather than "CO2 concentrations"