The Imminent Data Desert: The Future of Stratospheric Monitoring in a Rapidly Changing World

The Atmospheric Chemistry Experiment-Fourier Transform Spectrometer (ACE-FTS) on SCISAT-1 and the Microwave Limb Sounder (MLS) on NASA’s Aura satellite have contributed significantly to understanding the impacts of human activities on the stratospheric ozone layer. The two-decade-long data record from these instruments has allowed quantification of ozone depletion caused by human-released chlorofluorocarbons (CFCs) and other ozone-depleting substances (ODSs), the effects of extreme natural events like major volcanic eruptions including Hunga in 2022, as well as events amplified by human-caused climate change, such as wildfires that injected material into the stratosphere, as happened over Australia in late 2019 and early 2020. Both platforms are nearing the end of their operational lifetimes, and their decommissioning will cause a substantial gap in the measurement of critical atmospheric components, including water vapor, inorganic chlorine species, and tracers of stratospheric transport. This upcoming "data desert" poses significant challenges for monitoring the recovery of the ozone layer and assessing the effects of future extreme events on stratospheric composition. The lack of confirmed future missions that can provide daily near-global profile measurements of these stratospheric gases highlights the need for new observational strategies to bridge this impending gap. This paper discusses the essential role of ACE-FTS and MLS in advancing our understanding of the stratosphere, the impact of data loss after their decommissioning, and the urgency of developing strategies for mitigating the impacts of these observational losses at a time marked by dramatic changes in the stratosphere due to both natural and human factors.