Ozone Layer Evolution in the Early 20th Century

Abstract

The ozone layer is well observed since the 1930s from the ground and, since the 1980s, by satellite-based instruments. The evolution of ozone in the past is important because of its dramatic influence on the biosphere and humans but has not been known for most of the time, except for some measurements of near-surface ozone since the end of the 19th century. This gap can be filled by either modeling or paleo reconstructions. Here, we address ozone layer evolution during the early 20th century. This period was very interesting due to a simultaneous increase in solar and anthropogenic activity, as well as an observed but not explained substantial global warming. For the study, we exploited the chemistry-climate model SOCOL-MPIOM driven by all known anthropogenic and natural forcing agents, as well as their combinations. We obtain a significant global scale increase in the total column ozone by up to 12 Dobson Units and an enhancement of about 20% of the near-surface ozone over the Northern Hemisphere. We conclude that the total column ozone changes during this period were mainly driven by enhanced solar ultra violet (UV) radiation, while near-surface ozone followed the evolution of anthropogenic ozone precursors. This finding can be used to constrain the solar forcing magnitude.

Representativeness of the Arosa/Davos Measurements for the Analysis of the Global Total Column Ozone Behavior

“…The reconstructed historical TCO behavior agrees with a much more complicated approach based on the CCM modeling and data assimilation (HISTOZ; Brönnimann et al, 2013) with a correlation of about 0.5. It should be noted that the reconstructed TCO possesses a positive trend from 1926 to 1940 discussed by Egorova et al (2020) and observable in HISTOZ data. This should be studied further to understand the implication of the obtained results for the assessment of the solar forcing magnitude in the past.…”

“…It is interesting to note that the positive TCO trend from 1926 to 1940 obtained by Egorova et al (2020) using the CCM SOCOL-MPIOM driven by strong solar forcing is also visible in the reconstructed data. This fact can be interpreted as a support for a strong solar forcing (up to 4 W/m 2 in total solar irradiance from 1900 to 1940) during the early 20th century discussed also in Egorova et al (2018).…”

“…Our model experiments (Egorova et al, 2018) suggested that solar irradiance forcing should be much higher during the early 20th century (and on centennial timescales in principle) than commonly accepted to successfully simulate the observed climate warming. This hypothesis can be supported or denied by the comparison of the simulated and observed total ozone over Arosa reflecting solar UV changes during the considered period (Egorova et al, 2020). Therefore, it will be interesting to compare the simulated and observed historical total ozone trends to investigate whether the Arosa time series are representative of the regional and global scales.…”

Attribution of Stratospheric and Tropospheric Ozone Changes Between 1850 and 2014 in CMIP6 Models

“…They find that the increase in lower stratospheric ozone associated with the increase in ozone precursors contribute significantly to the total column ozone (TCO). Egorova et al (2020) use a coupled stratosphere-troposphere model, again with a reduced tropospheric chemistry, to study early-twentieth century ozone changes and find substantial anthropogenic influences on ozone already in this early period, driven by both anthropogenic and solar forcings.…”

“…Egorova et al. (2020) use a coupled stratosphere‐troposphere model, again with a reduced tropospheric chemistry, to study early‐twentieth century ozone changes and find substantial anthropogenic influences on ozone already in this early period, driven by both anthropogenic and solar forcings.…”