Radiative Forcing Focus Working Group


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    Working Group leads:  William (Bill) J. Collins, University of Reading, UK (w.collins @ reading.ac.uk)

                                            Fiona O’Connor, Met Office Hadley Centre, UK (fiona.oconnor @ metoffice.gov.uk)

                                            Pasquale Sellitto, LISA-UPEC, France (pasquale.sellitto @ lisa.u-pec.fr)

    TOAR-II Steering Committee liaison:  Helen Worden, National Center for Atmospheric Research, Boulder, USA, (hmw @ ucar.edu)

     Established:  March 18, 2021


The Radiative Forcing Focus Working Group has the following objectives:

It is essential to quantify the historical evolution of radiative forcing (RF) in order to understand the drivers of the climate response over the historical period. A substantial proportion of the human-induced RF has come from tropospheric ozone, hence a quantification of RF attributed to ozone precursors will be an important outcome. Quantification of ozone's RF since pre-industrial times is heavily dependent on our understanding of pre-industrial ozone levels. In the first phase of TOAR, TOAR-Climate (Gaudel et al., 2018) reported the present day distribution and trends of ozone using metrics relevant to climate studies, but was not able to go back in time beyond the 1970s. TOAR-Observations (Tarasick et al. 2019) provided the most comprehensive re-evaluation of all available historical ozone observations (pre-1975), and concluded that there are no reliable ozone observations before 1896. The quantification of pre-industrial to present day ozone RF and present to future RF in TOAR-II will therefore rely on atmospheric chemistry modelling. Global atmospheric chemistry models were evaluated as a component of the first phase of TOAR by TOAR-Model Performance (Young et al., 2018). Since then, new multi-model intercomparison studies running online chemistry, CCMI and AerChemMIP (e.g., Collins et al., 2017), have become available, and chemistry-transport models (CTMs) and chemistry-climate models (CCMs) have continued to advance in their sophistication and complexity.

This Focus Working Group will primarily:

(1) Review the current literature on ozone radiative forcing

(2) Assess the different methodologies for quantifying ozone radiative forcing

(3) Report best estimates of present, past and future ozone radiative forcing, using models and observations.


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