Increased concentration and vertical distribution of carbon dioxide in the stratosphere

Abstract

Although many measurements of the abundance of CO₂ in the troposphere have been made, knowledge of its stratospheric abundances and variability is sparse. Here we report mid-latitude vertical profiles of CO₂, up to 35 km, measured in 1979, 1982 and 1984 by analysing cryogenically collected balloon samples supplemented by air samples taken aboard aircraft. CO₂ mixing ratios are not constant with altitude but rather decrease by ∼7 p.p.m.v. (parts per 10⁶ by volume) from the tropopause to the mid-stratosphere. The growth rate of the atmospheric CO₂ abundance caused by anthropogenic emission, which varies between 1.0 and 1.5 p.p.m.v. yr^–1 at ground level¹, is also observed at all stratospheric heights up to 35 km. The shape of the profiles suggests that excess CO₂ above 20 km enters the stratosphere through tropical upwelling rather than mid-latitude diffusion. The time lag of this height region with respect to the tropospheric CO₂ level is ∼5 yr.