A. Engel et al., Age of stratospheric air unchanged within uncertainties over the past 30 years

Letter abstract

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Nature Geoscience 2, 28-31 (2009)
Published online: 14 December 2008 | doi:10.1038/ngeo388

Age of stratospheric air unchanged within uncertainties over the past 30 years

A. Engel¹, T. Möbius¹, H. Bönisch¹, U. Schmidt¹, R. Heinz², I. Levin², E. Atlas³, S. Aoki⁴, T. Nakazawa⁴, S. Sugawara⁵, F. Moore⁶, D. Hurst⁶, J. Elkins⁶, S. Schauffler⁷, A. Andrews⁶ and K. Boering⁸

The rising abundances of greenhouse gases in the atmosphere is associated with an increase in radiative forcing that leads to warming of the troposphere, the lower portion of the Earth's atmosphere, and cooling of the stratosphere above¹. A secondary effect of increasing levels of greenhouse gases is a possible change in the stratospheric circulation^{2, 3}, which could significantly affect chlorofluorocarbon lifetimes⁴, ozone levels^{5, 6} and the climate system more generally⁷. Model simulations have shown that the mean age of stratospheric air⁸ is a good indicator of the strength of the residual circulation⁹, and that this mean age is expected to decrease with rising levels of greenhouse gases in the atmosphere¹⁰. Here we use balloon-borne measurements of stratospheric trace gases over the past 30 years to derive the mean age of air from sulphur hexafluoride (SF₆) and CO₂ mixing ratios. In contrast to the models, these observations do not show a decrease in mean age with time. If models are to make valid predictions of future stratospheric ozone levels, and of the coupling between ozone and climate change, a correct description of stratospheric transport and possible changes in the transport pathways are necessary.

1. Institute for Atmospheric and Environmental Sciences, Goethe Universität Frankfurt, 60483 Frankfurt, Germany
2. Institut für Umweltphysik, Universität Heidelberg, 69120 Heidelberg, Germany
3. Division of Marine and Atmospheric Chemistry, University of Miami, Miami, FL 33149, USA
4. Centre for Atmospheric and Oceanic Studies, Tohoku University, Sendai 980-8578, Japan
5. Miyagi University of Education, Sendai 980-0845, Japan
6. Earth System Research Laboratory, NOAA, Boulder, CO 80305, USA
7. Atmospheric Chemistry Division, NCAR, Boulder, CO 80307-3000, USA
8. Departments of Chemistry and of Earth and Planetary Science, University of California, Berkeley, CA 94720-1460, USA

Correspondence to: A. Engel¹ e-mail: an.engel@iau.uni-frankfurt.de

Correspondence to: F. Moore⁶D. Hurst⁶ Also at Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA

Link to abstract: http://www.nature.com/ngeo/journal/v2/n1/abs/ngeo388.html