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

• Main Authors: Dhomse, Sandip, Kinnison, Douglas, Chipperfield, Martyn, Cionni, Irene, Hegglin, Michaela, Abraham, Luke, Akiyoshi, Hideharu, Archibald, Alex, Bednarz, Ewa Monika, Bekki, Slimane, Braesicke, Peter, Butchart, Neal, Dameris, Martin, Deushi, Makoto, Frith, Stacy, Hardiman, Steven, Hassler, Birgit, Horowitz, Larry, Hu, Rong-Ming, Jöckel, Patrick, Josse, Beatrice, Kirner, Oliver, Kremser, Stefanie, Langematz, Ulrike, Lewis, Jared, Marchand, Marion, Lin, Meiyun, Mancini, Eva, Marécal, Virginie, Michou, Martine, Morgenstern, Olaf, O'Connor, Fiona, Oman, Luke, Pitari, Giovanni, Plummer, David, Pyle, John, Revell, Laura, Rozanov, Eugene, Schofield, Robyn, Stenke, Andrea, Stone, Kane, Sudo, Kengo, Tilmes, Simone, Visioni, Daniele, Yamashita, Yousuke, Zeng, Guang
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2018
• Subjects: Antarctic; Arctic; The Antarctic; Antarc*; Climate change
• Online Access: https://eprints.lancs.ac.uk/id/eprint/124248/; https://doi.org/10.5194/acp-2018-8409-2018

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 2047 (with a 1-σ uncertainty of 2042–2052). At Southern Hemisphere mid-latitudes column ozone is projected to return to 1980 values in 2046 (2042–2050), and at Northern Hemisphere mid-latitudes in 2034 (2024–2044). In the polar regions, the return dates are 2062 (2055–2066) in the Antarctic in October and 2035 (2025–2040) in the Arctic in March. The earlier return dates in the NH reflect the larger sensitivity to dynamical changes. Our estimates of return dates are later than those presented in the 2014 Ozone Assessment by approximately 5–15 years, depending on the region. In the tropics only around half the models predict a return to 1980 values, at around 2040, while the other half do not reach this 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, which is the main driver of ozone loss and recovery. However, there are a few outliers which show that the multi-model ...