I know the data is messy so not sure how well it would work, but there's an obvious seasonal component to the concentration of CO₂ in the atmosphere. So much that in the first year, the experimenters were worried that their data was garbage because how could CO₂ concentration be going down in a place so far from civilization? But it turns out as a whole, it's like the Earth takes a breath every year. IIRC it's mainly related to more land mass on the Northern Hemisphere, and the terrestrial biosphere is more variable than the oceans are.

In theory, you should be able to decompose the signal into waves, and many will have a period of about one year. But I'm too lazy to actually try, er, I mean, an exercise left to the reader.