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Age of stratospheric air: Progress on processes, observations, and long-term trends Garny, H. Ploeger, F. Ábalos Álvarez, Marta Bönisch, H. Castillo, A. E. Clarmann, T. von Diallo, M. Engel, A. Laube, J. C. Linz, M. Neu, J. L. Podglajen, A. Ray, E. Rivoire, L. Saunders, L. N. Stiller, G. Voet, F. Wagenhäuser, T. Walker, K. A. 551.51 Stratospherecirculationage of airobservationsmodelstrends Circulation Age of air Observations Models Trends Ciencias Física atmosférica 22 Física 2501 Ciencias de la Atmósfera © 2024. The Author(s) 80NM0018D0004 Age of stratospheric air is a well established metric for the stratospheric transport circulation. Rooted in a robust theoretical framework, this approach offers the benefit of being deducible from observations of trace gases. Given potential climate‐induced changes, observational constraints on stratospheric circulation are crucial. In the past two decades, scientific progress has been made in three main areas: (a) Enhanced process understanding and the development of process diagnostics led to better quantification of individual transport processes from observations and to a better understanding of model deficits. (b) The global age of air climatology is now well constrained by observations thanks to improved quality and quantity of data, including global satellite data, and through improved and consistent age calculation methods. (c) It is well established and understood that global models predict a decrease in age, that is, an accelerating stratospheric circulation, in response to forcing by greenhouse gases and ozone depleting substances. Observational records now confirm long‐term forced trends in mean age in the lower stratosphere. However, in the mid‐stratosphere, uncertainties in observational records are too large to confirm or disprove the model predictions. Continuous monitoring of stratospheric trace gases and further improved methods to derive age from those tracers will be crucial to better constrain variability and long‐term trends from observations. Future work on mean age as a metric for stratospheric transport will be important due to its potential to enhance the understanding of stratospheric composition changes, address climate model biases, and assess the impacts of proposed climate geoengineering methods. European Commission Ministerio de Ciencia e Investigación (España) Agencia Estatal de Investigación (España) German Research Foundation Canadian Space Agency Natural Sciences and Engineering Research Council of Canada California Institute of Technology NASA Agence Nationale de la Recherche (France) Depto. de Física de la Tierra y Astrofísica Fac. de Ciencias Físicas TRUE pub 2026-07-17T17:26:32Z 2026-07-17T17:26:32Z 2024-10-21 review article VoR https://hdl.handle.net/20.500.14352/138701 8755-1209 10.1029/2023RG000832 1944-9208 eng info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2021-2023/PID2021-124772OB-I00/ES/RECUPERACION DE LA CAPA DE OZONO ESTRATOSFERICO EN EL HEMISFERIO NORTE EN UN CONTEXTO DE CAMBIO CLIMATICO/ ID 428312742 ID 462476233 16SUASCMEV RGPIN-2017-06664 80NM0018D0004 21-CE01-0016-01 Garny, H., Ploeger, F., Abalos, M., Bönisch, H., Castillo, A. E., von Clarmann, T., et al. (2024). Age of stratospheric air: Progress on processes, observations, and long‐term trends. Reviews of Geophysics, 62, e2023RG000832. https://doi.org/10. 1029/2023RG000832 Attribution 4.0 International http://creativecommons.org/licenses/by/4.0/ open access application/pdf American Geophysical Union; Wiley