Atmos. Chem. Phys. 18, 1379–1394 (2018).

The Montreal Protocol came into effect in 1989, limiting multiple ozone-depleting substances. Evidence suggests total column ozone has stabilized since the late 1990s, but has not increased as predicted by chemistry–climate models. To better understand the lack of total recovery, William Ball, from the Physikalisch–Meterologisches Observatorium Davos World Radiation Center, and colleagues combine multiple satellite measurements to quantify changes in total column ozone contributed by changes in the troposphere, and upper, middle, and lower stratosphere.

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They show upper stratospheric ozone has increased in almost all latitude bands between 60° S and 60° N since 1998, while lower stratospheric ozone has decreased. Stability in total column ozone is attributed to increases in tropospheric ozone counteracting the overall downward trend in stratospheric ozone. Current models do not reproduce the lower stratospheric ozone decrease. The authors posit several explanations for why, including climate change impacts on the Brewer–Dobson Circulation and the effects of unaccounted-for very-short-lived substances containing chlorine or bromine. Given the importance of ozone restoration for human health, a better understanding of the drivers of declining lower stratospheric ozone is needed.