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 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 ozone-depleting substances, the effects of extreme natural events like major volcanic eruptions including Hunga in 2022, and events amplified by human-caused climate change such as wildfires that inject material into the stratosphere, as happened over Australia in early 2020. The Aura platform is nearing the end of its operational lifetime, and SCISAT-1 is over 20 years old. 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 on stratospheric composition of future extreme events, threats posed by increases in space debris from satellite burn-up, and the possible injection of stratospheric aerosol to mitigate global warming. The lack of confirmed future missions that can provide daily near-global profile measurements of stratospheric composition highlights the need for 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 the cessation of one or both instruments, and the urgency of developing strategies for mitigating the impact of these observational losses at a time marked by dramatic changes in the stratosphere due to human and natural factors.

Significance Statement
We highlight the critical role that data from the ACE-FTS and Microwave Limb Sounder (MLS) satellite instruments have played in advancing our understanding of stratospheric composition and the impacts of human activities on the ozone layer. As these instruments near the end of their operational lifetimes, the imminent loss of data, particularly of stratospheric water vapor, chlorine species, and tracers of transport, portends profound and irrevocable gaps in atmospheric observations. This loss of observational capability will occur at a time of rapid climate change and hinder our understanding of the stratosphere’s response to, and its coupled role in, continued climate forcing. This paper emphasizes the urgency of addressing this data desert, highlighting the need for sustained, coordinated, global measurement capabilities for these crucial constituents.