Evaluating stratospheric ozone and water vapour changes in CMIP6 models from 1850 to 2100
<p>Stratospheric ozone and water vapour are key components of the Earth system, and past and future changes to both have important impacts on global and regional climate. Here, we evaluate long-term changes in these species from the pre-industrial period (1850) to the end of the 21st century i...
| Main Authors: | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2021-03-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/21/5015/2021/acp-21-5015-2021.pdf |
| Summary: | <p>Stratospheric ozone and water vapour are key components of the Earth system, and past and future changes to both have important impacts on global and
regional climate. Here, we evaluate long-term changes in these species from the pre-industrial period (1850) to the end of the 21st century
in Coupled Model Intercomparison Project phase 6 (CMIP6)
models under a range of future emissions scenarios. There is good agreement between the CMIP multi-model mean and observations for total column
ozone (TCO), although there is substantial variation between the individual CMIP6 models. For the CMIP6 multi-model mean, global mean TCO has
increased from <span class="inline-formula">∼</span> 300 <span class="inline-formula">DU</span> in 1850 to <span class="inline-formula">∼</span> 305 <span class="inline-formula">DU</span> in 1960, before rapidly declining in the 1970s and 1980s following the
use and emission of halogenated ozone-depleting substances (ODSs). TCO is projected to return to 1960s values by the middle of the 21st century
under the SSP2-4.5, SSP3-7.0, SSP4-3.4, SSP4-6.0, and SSP5-8.5 scenarios, and under the SSP3-7.0 and SSP5-8.5 scenarios TCO values are projected to
be <span class="inline-formula">∼</span> 10 <span class="inline-formula">DU</span> higher than the 1960s values by 2100. However, under the SSP1-1.9 and SSP1-1.6 scenarios, TCO is not projected to
return to the 1960s values despite reductions in halogenated ODSs due to decreases in tropospheric ozone mixing ratios. This global pattern is
similar to regional patterns, except in the tropics where TCO under most scenarios is not projected to return to 1960s values, either through
reductions in tropospheric ozone under SSP1-1.9 and SSP1-2.6, or through reductions in lower stratospheric ozone resulting from an acceleration of
the Brewer–Dobson circulation under other Shared Socioeconomic Pathways (SSPs). In contrast to TCO, there is poorer agreement between the
CMIP6 multi-model mean and observed lower
stratospheric water vapour mixing ratios, with the CMIP6 multi-model mean underestimating observed water vapour mixing ratios by
<span class="inline-formula">∼</span> 0.5 <span class="inline-formula">ppmv</span> at 70 <span class="inline-formula">hPa</span>. CMIP6 multi-model mean stratospheric water vapour mixing ratios in the tropical lower stratosphere have
increased by <span class="inline-formula">∼</span> 0.5 <span class="inline-formula">ppmv</span> from the pre-industrial to the present-day period and are projected to increase further by the end of the 21st
century. The largest increases (<span class="inline-formula">∼</span> 2 <span class="inline-formula">ppmv</span>) are simulated under the future scenarios with the highest assumed forcing pathway
(e.g. SSP5-8.5). Tropical lower stratospheric water vapour, and to a lesser extent TCO, shows large variations following explosive volcanic eruptions.</p> |
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| ISSN: | 1680-7316 1680-7324 |