EGU25-11349, updated on 15 Mar 2025
https://doi.org/10.5194/egusphere-egu25-11349
EGU General Assembly 2025
© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.
Comparing radiative forcing measures for ozone
William Collins1, Fiona O'Connor2,3, Rachael Byrom4, Øivind Hodnebrog4, Patrick Jöckel5, Mariano Mertens5, Gunnar Myhre4, Matthias Nützel5, Dirk Olivié6, Ragnhild Skeie4, Laura Stecher5, Larry Horowitz7, Vaishali Naik7, and Lee Murray8
William Collins et al.
  • 1University of Reading, Meteorology, Reading, United Kingdom of Great Britain – England, Scotland, Wales (w.collins@reading.ac.uk)
  • 2Met Office Hadley Centre, Exeter, United Kingdom
  • 3Department of Mathematics & Statistics, Global Systems Institute, University of Exeter, United Kingdom
  • 4CICERO Center for International Climate Research Oslo, Norway
  • 5Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 6Norwegian Meteorological Institute, Oslo, Norway
  • 7NOAA Geophysical Fluid Dynamics Laboratory, Princeton, NJ, USA
  • 8Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, USA

Ozone is the third most important greenhouse gas, contributing a forcing of 0.47 W/m2 over the historical period. All assessments of ozone forcing so far have used the stratospheric-temperature adjusted radiative forcing (SARF) calculated by offline radiative transfer models. The two most recent IPCC reports have recommended the use of effective radiative forcing (ERF) as the preferred measure of forcing, but no calculations have been available.

For the first time we calculate the future ozone online ERF from six Earth system models and compare this to the SARF calculations. The future ozone calculations are for the SSP3-7.0 scenario for the year 2050. Only the ozone changes (and any consequent impacts on meteorology) are included in the radiative forcing calculations. We find an ERF of 0.27+/- 0.09 Wm-2  and an ozone column increase of 12 DU. Approximately half of the forcing change comes from ozone recovery following the decline in halocarbons.

By decomposing the radiative forcing into instantaneous (IRF), stratospheric-temperature adjusted (SARF) and effective (ERF) radiative forcing we gain insights into the adjustment processes causing the differences between the radiative forcing measures. The ERF is typically larger than the SARF. This is mostly due to positive non-cloud adjustments through increased water vapour (particularly in the stratosphere) and decreased surface albedo. Reductions in high and mid-level cloud increase the short-wave forcing, but decrease the long-wave forcing. The adjustments to the forcing depend on the altitude of the ozone change, with adjustments to ozone changes following reductions in ozone-depleting substances being more strongly positive than those following increases in ozone precursors.

How to cite: Collins, W., O'Connor, F., Byrom, R., Hodnebrog, Ø., Jöckel, P., Mertens, M., Myhre, G., Nützel, M., Olivié, D., Skeie, R., Stecher, L., Horowitz, L., Naik, V., and Murray, L.: Comparing radiative forcing measures for ozone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11349, https://doi.org/10.5194/egusphere-egu25-11349, 2025.