Time of Emergence for the Influence of Climate Change on Surface Ozone

One of the many projected impacts of 21st century climate change is modification of surface air quality. Many previous studies have investigated the question of whether surface ozone and fine particulate matter (PM_2.5) are expected to evolve over this period as a result of climate change, but few have considered the role of interannual variability and the predictability of these changes. Building on prior work, we investigate the predictability of such changes in surface ozone over the next 80 years. We use the GEOS-Chem High Performance model to perform high-fidelity, 100-year air quality simulations, driven by an ensemble of climate simulations from the Community Atmosphere Model. We focus on the question of how long it will take for the impacts of climate change on surface ozone to be visible against background variability, assuming no change in emissions of air quality-relevant pollutants such as nitrogen and sulfur oxides. We quantify not only how this “time of emergence” varies by location worldwide, but also the magnitude of the potential error which could result from projections based on short time-slice simulations. Our results demonstrate the importance of transient simulations in long-term air quality forecasting while providing the first estimate of the time of emergence for climate-driven ozone impacts in multiple populated regions worldwide. Finally, this work provides further insight into the challenges associated with monitoring and assessing the impacts of external forcings on regional air quality, such as for implementation of emissions policy under large interannual climate variability.