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Discussion papers | Copyright
https://doi.org/10.5194/cp-2018-115
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 24 Sep 2018

Research article | 24 Sep 2018

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Climate of the Past (CP).

Role of the stratospheric chemistry-climate interactions in the hot climate conditions of the Eocene

Sophie Szopa1, Rémi Thiéblemont1, Slimane Bekki2, Svetlana Botsyun1,a, and Pierre Sepulchre1 Sophie Szopa et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, LSCE-IPSL, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 2Laboratoire, Milieux, Observations Spatiales, Institut Pierre Simon Laplace, CNRS, Paris, France
  • anow at: Department of Geosciences, University of Tübingen, Germany

Abstract. The stratospheric ozone layer plays a key role in atmospheric thermal structure and circulation. Although stratospheric ozone distribution is sensitive to changes in composition and climate, the modifications of stratospheric ozone are not usually considered in climate studies at geological time scales. Here, we evaluate with a chemical-climate model the potential role of stratospheric ozone chemistry in the case of the Eocene hot conditions. We show that the structure of the ozone layer is significantly different under these conditions (4×CO2 climate and high concentrations of tropospheric N2O and CH4). While at mid and high latitudes, the total column ozone is found to be enhanced, the tropical ozone column remains more or less unchanged. These ozone changes are related to the stratospheric cooling and an acceleration of stratospheric Brewer-Dobson circulation simulated under Eocene climate. The meridional distribution of the total ozone column appears also to be strongly modified, showing particularly pronounced mid-latitudes maxima and steeper negative poleward gradient from these maxima. These anomalies are consistent with changes in the seasonal evolution of the polar vortex during the winter, especially in the Northern Hemisphere. Compared to a pre-industrial atmospheric composition, the changes in local ozone concentration reach up to 40% for zonal annual mean and affect temperature by a few Kelvins in the middle stratosphere.

As inter-model differences in simulating the deep past temperatures are quite high, the consideration of atmospheric chemistry, which is computationally demanding in Earth system models, may seem superfluous. However, our results suggest that using stratospheric ozone calculated by the model (and hence more physically consistent with Eocene conditions) instead of the commonly specified preindustrial ozone distribution can change the simulated global surface air temperature by 14%. This error is of the same order as the effect of non-CO2 boundary conditions (topography, bathymetry, solar constant & vegetation). Moreover, the results highlight the sensitivity of stratospheric ozone to hot climate conditions. Since the climate sensitivity to stratospheric ozone feedback largely differs between models, it must be better constrained not only for deep past conditions but also for future climates.

Sophie Szopa et al.
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Short summary
The stratospheric ozone layer plays a key role in atmospheric thermal structure and circulation. Here, we evaluate with a chemical-climate model the potential role of stratospheric ozone chemistry in the case of the Eocene hot conditions. Our results suggest that using stratospheric ozone calculated by the model instead of the commonly specified preindustrial ozone distribution can change the simulated global surface air temperature by 14 %.
The stratospheric ozone layer plays a key role in atmospheric thermal structure and circulation....
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