The carbon dioxide concentration in Earth's upper atmosphere is increasing at more than twice the average rate observed at the surface.

Jia Yue of Hampton University in Virginia and his colleagues analysed CO2 measurements at different atmospheric heights and latitudes between 2002 and 2014 using a satellite-borne infrared radiometer. They found that CO2 levels increased at a peak rate of 12% per decade at a height of 110 kilometres, with more pronounced rises in the Northern Hemisphere than in the Southern Hemisphere. The rate of CO2 increase in the atmosphere below 80 kilometres is only about 5% per decade.

The fast build-up of CO2 in the upper atmosphere, which climate models fail to reproduce, points to increased vertical mixing. This will probably not affect greenhouse warming at Earth's surface, but could eventually change the upper atmosphere's density and alter the altitude of satellites in orbit, the authors suggest.

Geophys. Res. Lett. (2015)