The oscillating atmospheric CO[subscript 2] concentrations at Mauna Loa, on the island of Hawaii, Hawaii, United States of America, are Fourier transformed in order to extract the period of oscillations. Also well-known as the Keeling curve, CO[subscript 2] concentrations (in time series) at Mauna Loa oscillate in direct association with seasonal fluctuations in the northern hemisphere. Thus, the period of oscillations of atmospheric CO[subscript 2] concentrations is equal to Earth's orbital period. In error by only 3.1%, we obtained 11.63 months. With the oscillating and increasing trend of the Keeling curve being directly associated with Earth's geography, vegetation, photosynthesis, the seasons, global warming, and climate change, the current work is perceived as an enriching activity on the application of Fourier transformation--and on a non-Newtonian approach to determining an astronomical quantity