1NASA Goddard Space Flight Center, Greenbelt, MD, USA
2Science Systems and Applications, Inc., Lanham, MD, USA
3Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA
Abstract. The long-term stratospheric impacts due to emissions of CO2, CH4, N2O, and ozone depleting substances (ODSs) are investigated using an updated version of the Goddard two-dimensional (2-D) model. Perturbation simulations with the ODSs, CO2, CH4, and N2O varied individually are performed to isolate the relative roles of these gases in driving stratospheric changes over the 1850–2100 time period. We also show comparisons with observations and the Goddard Earth Observing System chemistry-climate model simulations for the time period 1960–2100 to illustrate that the 2-D model captures the basic processes responsible for long-term stratospheric change.
The 2-D simulations indicate that prior to 1940, the ozone increases due to CO2 and CH4 loading outpace the ozone losses due to increasing N2O and carbon tetrachloride (CCl4) emissions, so that ozone reaches a broad maximum during the 1920s–1930s. This preceeds the significant ozone depletion during ~1960–2050 driven by the ODS loading. During the latter half of the 21st century as ODS emissions diminish, CO2, N2O, and CH4 loading will all have significant impacts on global total ozone based on the IPCC A1B (medium) scenario, with CO2 having the largest individual effect. Sensitivity tests illustrate that due to the strong chemical interaction between methane and chlorine, the CH4 impact on total ozone becomes significantly more positive with larger ODS loading. The model simulations also show that changes in stratospheric temperature, Brewer-Dobson circulation (BDC), and age of air during 1850–2100 are controlled mainly by the CO2 and ODS loading. The simulated acceleration of the BDC causes the age of air to decrease by ~1 year from 1860–2100. The corresponding photochemical lifetimes of N2O, CFCl3, CF2Cl2, and CCl4 decrease by 11–13% during 1960–2100 due to the acceleration of the BDC, with much smaller lifetime changes (<4%) caused by changes in the photochemical loss rates.