Estimates of Ozone Return Dates from Chemistry-Climate Model Initiative Simulations

• Main Authors: Dhomse, SS, Kinnison, D, Chipperfield, MP, Salawitch, RJ, Cionni, I, Hegglin, MI, Abraham, NL, Akiyoshi, H, Archibald, AT, Bednarz, EM, Bekki, S, Braesicke, P, Butchart, N, Dameris, M, Deushi, M, Frith, S, Hardiman, SC, Hassler, B, Horowitz, LW, Hu, R-M, Jöckel, P, Josse, B, Kirner, O, Kremser, S, Langematz, U, Lewis, J, Marchand, M, Lin, M, Mancini, E, Marécal, V, Michou, M, Morgenstern, O, O Connor, FM, Oman, L, Pitari, G, Plummer, DA, Pyle, JA, Revell, LE, Rozanov, E, Schofield, R, Stenke, A, Stone, K, Sudo, K, Tilmes, S, Visioni, D, Yamashita, Y, Zeng, G
• Format: Article in Journal/Newspaper
• Language: English
• Published: European Geosciences Union 2018
• Subjects: Arctic; Antarctic; The Antarctic; Antarc*; Climate change
• Online Access: https://eprints.whiterose.ac.uk/132294/; https://eprints.whiterose.ac.uk/132294/1/acp-18-8409-2018.pdf; https://eprints.whiterose.ac.uk/132294/6/acp-18-8409-2018-supplement.pdf

We analyse simulations performed for the Chemistry-Climate Model Initiative (CCMI) to estimate the return dates of the stratospheric ozone layer from depletion caused by anthropogenic stratospheric chlorine and bromine. We consider a total of 155 simulations from 20 models, including a range of sensitivity studies which examine the impact of climate change on ozone recovery. For the control simulations (unconstrained by nudging towards analysed meteorology) there is a large spread (±20 DU in the global average) in the predictions of the absolute ozone column. Therefore, the model results need to be adjusted for biases against historical data. Also, the interannual variability in the model results need to be smoothed in order to provide a reasonably narrow estimate of the range of ozone return dates. Consistent with previous studies, but here for a Representative Concentration Pathway (RCP) of 6.0, these new CCMI simulations project that global total column ozone will return to 1980 values in 2049 (with a 1σ uncertainty of 2043–2055). At Southern Hemisphere mid-latitudes column ozone is projected to return to 1980 values in 2045 (2039–2050), and at Northern Hemisphere mid-latitudes in 2032 (2020–2044). In the polar regions, the return dates are 2060 (2055–2066) in the Antarctic in October and 2034 (2025–2043) in the Arctic in March. The earlier return dates in the Northern Hemisphere reflect the larger sensitivity to dynamical changes. Our estimates of return dates are later than those presented in the 2014 Ozone Assessment by approximately 5–17 years, depending on the region, with the previous best estimates often falling outside of our uncertainty range. In the tropics only around half the models predict a return of ozone to 1980 values, around 2040, while the other half do not reach the 1980 value. All models show a negative trend in tropical total column ozone towards the end of the 21st century. The CCMI models generally agree in their simulation of the time evolution of stratospheric chlorine and bromine, ...