Detection of trends in surface ozone in the presence of climate variability

Abstract:

Trends in surface ozone can be driven by trends in ozone precursor emissions but also by trends in the meteorology. Here, we highlight the extent to which unforced, low-frequency climate variability can drive multi-decadal trends in ozone. Using output from six experiments of the GFDL chemistry climate model (CM3), we demonstrate that 20-year trends in surface ozone driven by climate variability alone can be as large or larger than those forced by changes in ozone precursor emissions or by anthropogenic climate change over the same period. We highlight regions and seasons where seasonal surface ozone is more (less) influenced by climate variability, and thus, where forced trends may be more (less) difficult to detect. The time of emergence of forced trends in ozone between 2006-2055 is shown to be most dependent on changes in ozone precursor emissions and the regional unforced climate variability, while the impact of anthropogenic climate change is shown to be comparatively small.