CO<sub>2</sub> surface variability: from the stratosphere or not?

Abstract. Fluctuations in atmospheric CO2 can be measured with great precision and are used to identify human-driven sources as well natural cycles of ocean land carbon. One source variability is the stratosphere, where influx aged CO2-depleted air produce fluctuations at surface. This process has been speculated a potential interannual (IAV) that might obscure quantification other IAV. Given recent success demonstrating stratospheric N2O- chlorofluorocarbon-depleted dominant their surface IAV Southern Hemisphere, I apply same model measurement analysis here CO2. Using chemistry-transport modeling or scaling observed N2O variability, find stratosphere-driven most 10 % not an important source. Diagnosing amplitude annual cycle its increase from 1985 2021 through variance gives rates similar traditional methods Northern Hemisphere (BRW, MLO) but emergence small trends (0.08 ppm per decade) (SMO, CGO).