Ozone Depleting Substances: Key Drivers of Past and Future BDC Trends

One of the most robust modeling results regarding the future evolution of Brewer-Dobson circulation (BDC) circulation is that it will be accelerated by increasing well-mixed greenhouse gases (GHG) over the 21st century. In several recent studies, however, it has become clear that ozone depleting substances (ODS) are also key drivers of BDC trends. We will present results from single-forcing model integrations, and multi-model intercomparison projects, showing that ODS are as important as GHG in terms of driving BDC trends. In the second half of the 20th century, ODS have contributed at least as much as GHG to accelerating the BDC; and, as a consequence of the Montreal Protocol, ODS will substantially decelerate the BDC in the 21st century, opposing the impact of GHG in the coming decades. We will also discuss how ODS act on the BDC via two distinct pathways. The first is chemical, and involves that depletion/recovery of stratospheric ozone, notably over the South Pole. The second is purely radiative, as ODS are also powerful greenhouse gases, and are therefore able to affect sea-surface temperatures just like CO2 and other well-mixed GHG.