On the secular trend of COx and CO₂ in the lower thermosphere

The estimated trend (~9% per decade) is about a factor of 2 larger than the rate of increase that can be ascribed to anthropogenic emissions of CO₂ (~5% per decade).

Here we investigate whether the observed trends of CO₂ and COx can be reproduced using the Whole Atmosphere Community Climate Model (WACCM), a comprehensive global model with interactive chemistry, wherein vertical eddy diffusion is estimated from a parameterization of gravity wave breaking that can respond to changes in the model climate. We find that the modeled trends of CO₂ and COx do not differ significantly at any altitude from the value expected from anthropogenic increases of CO₂ and that WACCM does not produce significant changes in eddy diffusivity.