Stratospheric Ozone Depletion, the Montreál Protocol and Paths to Recovery

Program Scientist, Atmospheric Composition,

Earth Science Division, Science Mission Directorate,

NASA Headquarters

In 1974, ground-breaking papers by Stolarski and Cicerone and Molina and Rowland alerted the world to the threat that chlorine species, in particular chlorofluoromethanes (CFCs), posed to stratospheric ozone. The unexpected discovery of profound springtime ozone losses over the Antarctic by Farman et al. (1985) and Bhartia et al. (1985) paved the way for the adoption of the Montreál Protocol in 1987 and its subsequent Amendments. The Protocol has imposed phase-outs in the production of ozone-depleting substances (ODSs) such as CFCs, and satellite observations indicate that stratospheric ozone is on its way to recovery in the coming decades. This success story is not simply one of international cooperation at the highest levels – it is the result of decades of global observations and the research and monitoring that these observations underpin. In the last ten years, the importance of surface-based monitoring to ensure compliance with the Montreal Protocol has been clearly demonstrated. However, it has been satellite observations of instruments such as the Microwave Limb Sounder (MLS) on the NASA Aura satellite and the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) on Canada’s SCISAT that for over 20 years have enabled the scientific community to understand the evolving chemistry and dynamics in the stratosphere that have accounted for the recovery of ozone to date. This growing understanding has allowed the science community to provide input to the Montreál Protocol process since its inception and has led directly to the adoption of the succeeding Amendments to the Protocol. No satellite instrument lasts forever, and the Aura satellite will reach End of Mission in the next 12-18 months. With the loss of the over 3,000 profiles of multiple trace species around the globe that MLS provides, there will be a multi-year gap in observations of critical components of ozone chemistry in the stratosphere, most significantly for halogens and water vapor. While it is expected that the ozone recovery will continue, the coming gap in the observational system will restrict the scientific community’s ability to fully understand the trajectory of the recovery and to provide scientific input to the Protocol process.

Selkirk has served Program Scientist in the Atmospheric Composition Focus Area in the Earth Science Division at NASA Headquarters since 2020. Prior to coming to Headquarters, Selkirk had worked as a research scientist in the Atmospheric Chemistry and Dynamics Laboratory at NASA Goddard Space Flight Center since 2008 and in the Earth Science Division at NASA Ames Research Center since 1988. He received a PhD in Meteorology from the Massachusetts Institute of Technology in 1986 under Prof. Reginald E. Newell and a BA from The Evergreen State College in Olympia, WA in 1977. Selkirk is a native of Buffalo and grew up in East Aurora, NY where he now resides.