Recovery of the Ozone Layer

Wuhu Feng, Sandip Dhomse, Ryan Hossaini and Martyn Chipperfield

Background

Past increases in stratospheric chlorine and bromine have depleted stratospheric ozone globally since the 1980s (see Figure 1). Due to the Montreal Protocol the production and emission of halogen-containing compounds has been significantly reduced or stopped altogether. Therefore, we expect the stratospheric loading of chlorine and bromine will decrease slowly (i.e. over next 50 years) and the ozone layer will ‘recover’. Part of our research is concerned with detecting and understanding these chlorine/bromine trends and to predict the extent and timing of ozone layer recovery. We are also interested in the climate impact of the recovering ozone layer.

<b>Figure 1:</b> Schematic showing stages of ozone layer depletion and recovery. (From <a href="http://www.esrl.noaa.gov/csd/assessments/ozone/2006/">WMO 2007 Chapter 6</a href>).

Past Chlorine and Bromine Trends

Observations from the ground (Koehlhep et al., 2012 ) and satellite (Brown et al., 2011) have shown that past increases in chlorine (and bromine) loading has slowed and since the 1990s is now decreasing. Our 3D model, forced with observed surface concentrations, reproduces these stratospheric trends, showing that we have a good understanding of the chlorine and bromine budgets.

Future Ozone Predictions

As part of SPARC CCMVal-2 and WMO/UNEP ozone assessments we have run a coupled chemistry-climate model to predict the return dates of stratospheric ozone (e.g. see Eyring et al., 2010).

Radiative Effect of Ozone Recovery

Past stratospheric ozone depletion has acted to cool the Earth’s surface, thereby offsetting warming due to increasing greenhouse gases (Figure 2). Therefore, one might expect recovery of the ozone layer to reverse this and for the future increase in stratospheric ozone to warm the surface. However, as shown from our model calculations in Figure 3, the recovery of the ozone layer is not uniform. Decreasing chlorine, and warmer temperatures, increase ozone in the mid-upper stratosphere and at high latitudes. However, in the tropical lower troposphere the models predict less ozone in 2100 due to increased upwelling. This tropical region plays a key role in the radiative impact. Therefore, it is possible that stratospheric ozone recovery will not reverse the cooling effect of past depletion (see Bekki et al (2013) for more information).

<br><b>Figure 2:</b> Radiative forcing (Wm<sup>-2</sup>) from 1750 to 2005 due to different forcings. A positive radiative forcing (e.g. increase in CO<sub>2</sub>) acts to warm the surface. A negative radiative forcing (e.g. decrease in stratospheric ozone) acts to cool the surface. (From <a href="http://www.ipcc.ch/publications_and_data/ar4/wg1/en/contents.html">IPCC (2007) Chapter 2</a href>.)<p>

<br><b>Figure 3:</b> Difference in O<sub>3</sub> mixing ratio between 2100 and 2000 from CCMVal model runs for (a) multi-model mean (MMM), (b) standard deviation of MMM, (c) MMM +1 σ and (d) MMM -1 σ. White dotted line indicates tropopause. In panel (a) ozone has increased (‘recovered’) throughout most of the stratosphere except in tropical lower stratosphere where it decreases due to enhanced upwelling. (From Bekki et al (2013).)<p>

Publications

Bekki, S., A. Rap, V. Poulain, S. Dhomse, M. Marchand, F. Lefevre, P.M. Forster, S. Szopa, M.P. Chipperfield, Climate impact of stratospheric ozone recovery, Geophys. Res. Lett., 40, 2796-2800 doi:10.1002/grl50358, 2013.

Brown A.T.; M.P. Chipperfield, C. Boone, C. Wilson, K. Walker, P. Bernath, Trends in atmospheric halogen containing gases since 2004, J. Quant. Spectrospcopy & Radiative Trans., 112 (16), 2552-2566, doi:10.1016/j.jqsrt.2011.07.005, 2011.

Eyring, V., I. Cionni, G. E. Bodeker, A. J. Charlton-Perez, D. E. Kinnison, J. F. Scinocca, D. W. Waugh, H. Akiyoshi, S. Bekki, M. P. Chipperfield, M. Dameris, S. Dhomse, S. M. Frith, H. Garny, A. Gettelman, A. Kubin, U. Langematz, E. Mancini, M. Marchand, T. Nakamura, L. D. Oman, S. Pawson, G. Pitari, D. A. Plummer, E. Rozanov, T. G. Shepherd, K. Shibata, W. Tian, P. Braesicke, S. C. Hardiman, J. F. Lamarque, O. Morgenstern, D. Smale, J. A. Pyle, and Y. Yamashita, Multi-model assessment of stratospheric ozone return dates and ozone recovery in CCMVal-2 models, Atmos. Chem. Phys., 10, 9451-9472, doi:10.5194/acp-10-9451-2010, 2010.

Hossaini, R.; Chipperfield, M. P.; Dhomse, S.; Ordonez, C; Saiz-Lopez, A; Abraham, NL; Archibald, A; Braesicke, P; Telford, P; Warwick, N; Yang, X; Pyle, J, Modelling future changes to the stratospheric source gas injection of biogenic bromocarbons
Geophys. Res. Lett., 39, L20813, doi:10.1029/2012GL053401, 2012.

Kohlhepp, R.; Ruhnke, R.; Chipperfield, M. P.; De Maziere, M; Notholt, J; Barthlott, S; Batchelor, RL; Blatherwick, RD; Blumenstock, T; Coffey, MT; Demoulin, P; Fast, H; Feng, W; Goldman, A; Griffith, DWT; Hamann, K; Hannigan, JW; Hase, F; Jones, NB; Kagawa, A; Kaiser, I; Kasai, Y; Kirner, O; Kouker, W; Lindenmaier, R; Mahieu, E; Mittermeier, RL; Monge-Sanz, B; Morino, I; Murata, I; Nakajima, H; Palm, M; Paton-Walsh, C; Raffalski, U; Reddmann, T; Rettinger, M; Rinsland, CP; Rozanov, E; Schneider, M; Senten, C; Servais, C; Sinnhuber, BM; Smale, D; Strong, K; Sussmann, R; Taylor, JR; Vanhaelewyn, G; Warneke, T; Whaley, C; Wiehle, M; Wood, SW, Observed and simulated time evolution of HCl, ClONO2, and HF total column abundances
Atmos. Chem. Phys., 12, 3527-3556, doi:10.5194/acp-12-3527-2012, 2012.