I am trying to understand the atmospheric ppm data, specifically around how CH4 decays to CO2.
This data says 2017 CH4 is about 1850ppm, and 2017 CO2 is 402ppm increasing about 3ppm/year. (https://www.eea.europa.eu/data-and-maps/daviz/atmospheric-concentration-of-carbon-dioxide-5)
I've also read that CH4 has a half-life in the atmosphere of about 9 years, decaying with the chemical equation CH4 + O2 → CO2 + H4
So if you'd expect methane's 1850ppm to decay to 925ppm over 9 years, that means you'd also expect to see an increase of 925ppm of CO2, or about 100ppm/yr just from methane decay. That'd be insanely high. But the data I linked earlier shows an increase of 3ppm.
So what am I missing in this analysis?