The first thing that must be understood in this paper is the chain of events that is being tracked. From the Sun’s rotational quirks, to their effects on CO2 in the respective atmospheres of Mars and Earth. There is also a comparison to older, normalized data from Venus.
Interestingly, once the data was compiled, there was no correlation found between the levels of CO2 found in the upper atmosphere (~150km on Earth, where this transformation takes place.) Broadening their search, the authors found a strong correlation between the ratio of CO2/O2 and the thermal changes. They feel this suggests that the thermal diffusion effect relies on some form of resonance between the two molecules involved