Preprint version. Published in International Journal of Climatology, Volume 19, Issue 8, June 30, 1999, pages 813-819.
NOTE: At the time of publication, the author Gary B. Hughes was not yet affiliated with Cal Poly.
The definitive version is available at https://doi.org/10.1002/(SICI)1097-0088(19990630)19:8<813::AID-JOC387>3.0.CO;2-#.
The frequency spectrum of Northern Hemisphere atmospheric CO2 concentration shows strong periodicities at 6.2, 1.0 and 0.5 years. The 6.2 year cyclicity has been attributed to non-linear interactions between the annual cycle and the atmospheric pole tide. The yearly signal is linked to terrestrial photosynthesis; phase analysis shows that annual CO2 minima occur at a lag of approximately 85 days from insolation maxima. Variations in the nominal yearly period occur during times of anomalous anthropogenic CO2 production. Periodicity at 6 months represents a deviation of the yearly signal from an annual sinusoid. If the yearly signal is largely sinusoidal, a plausible source of the 6 month periodicity could be cyclic phytoplankton productivity driven by natural insolation modes. Together, the three largest spectral peaks account for over 99% of the variation in detrended CO2 data.
Statistics and Probability
This is the pre-peer reviewed version of the following article:Spectral indications of unexpected contributors to atmospheric CO2 variability?, Gary B. Hughes, Robert Giegengack, and Haralambos N. Kritikos International Journal of Climatology, 19:8, Published by Wiley-Blackwell.