Chemical and climatic drivers of radiative forcing due to changes in stratospheric and tropospheric ozone over the 21st century
The ozone radiative forcings (RFs) resulting from projected changes in climate, ozone-depleting substances (ODSs), non-methane ozone precursor emissions and methane between the years 2000 and 2100 are calculated using simulations from the UM-UKCA chemistry–climate model (UK Met Office's Uni...
| Main Authors: | , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-02-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://www.atmos-chem-phys.net/18/2899/2018/acp-18-2899-2018.pdf |
| Summary: | The ozone radiative forcings (RFs) resulting from projected changes in
climate, ozone-depleting substances (ODSs), non-methane ozone precursor
emissions and methane between the years 2000 and 2100 are calculated using
simulations from the UM-UKCA chemistry–climate model (UK Met Office's
Unified Model containing the United Kingdom Chemistry and Aerosols
sub-model). Projected measures to improve air-quality through reductions in
non-methane tropospheric ozone precursor emissions present a co-benefit for
climate, with a net global mean ozone RF of −0.09 W m<sup>−2</sup>. This is
opposed by a positive ozone RF of 0.05 W m<sup>−2</sup> due to future decreases
in ODSs, which is driven by an increase in tropospheric ozone through
stratosphere-to-troposphere transport of air containing higher ozone amounts.
An increase in methane abundance by more than a factor of 2 (as projected by
the RCP8.5 scenario) is found to drive an ozone RF of 0.18 W m<sup>−2</sup>,
which would greatly outweigh the climate benefits of non-methane tropospheric
ozone precursor reductions. A small fraction (∼ 15 %) of the ozone RF
due to the projected increase in methane results from increases in
stratospheric ozone. The sign of the ozone RF due to future changes in
climate (including the radiative effects of greenhouse gases, sea surface
temperatures and sea ice changes) is shown to be dependent on the greenhouse
gas emissions pathway, with a positive RF (0.05 W m<sup>−2</sup>)
for RCP4.5 and a negative RF (−0.07 W m<sup>−2</sup>) for the RCP8.5
scenario. This dependence arises mainly from differences in the contribution to RF
from stratospheric ozone changes. Considering the increases in tropopause
height under climate change causes only small differences (≤ |0.02| W m<sup>−2</sup>) for the stratospheric, tropospheric and whole-atmosphere
RFs. |
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| ISSN: | 1680-7316 1680-7324 |