Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes
<p>Many modelling studies suggest that the El Niño–Southern Oscillation (ENSO), in interaction with the tropical Pacific background climate, will change with rising atmospheric greenhouse gas concentrations. Solar geoengineering (reducing the solar flux from outer space) has been proposed as a...
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| Format: | Article |
| Language: | English |
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Copernicus Publications
2020-12-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/20/15461/2020/acp-20-15461-2020.pdf |
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| author | A. Malik A. Malik A. Malik P. J. Nowack P. J. Nowack P. J. Nowack P. J. Nowack J. D. Haigh J. D. Haigh L. Cao L. Atique Y. Plancherel |
| author_facet | A. Malik A. Malik A. Malik P. J. Nowack P. J. Nowack P. J. Nowack P. J. Nowack J. D. Haigh J. D. Haigh L. Cao L. Atique Y. Plancherel |
| author_sort | A. Malik |
| collection | DOAJ |
| description | <p>Many modelling studies suggest that the El Niño–Southern Oscillation
(ENSO), in interaction with the tropical Pacific background climate, will
change with rising atmospheric greenhouse gas concentrations. Solar
geoengineering (reducing the solar flux from outer space) has been proposed
as a means to counteract anthropogenic climate change. However, the
effectiveness of solar geoengineering concerning a variety of aspects of
Earth's climate is uncertain. Robust results are particularly challenging to
obtain for ENSO because existing geoengineering simulations are too short
(typically <span class="inline-formula">∼</span> 50 years) to detect statistically significant
changes in the highly variable tropical Pacific background climate. We here
present results from a 1000-year-long solar-geoengineering simulation, G1,
carried out with the coupled atmosphere–ocean general circulation model
HadCM3L. In agreement with previous studies, reducing the solar irradiance
(4 %) to offset global mean surface warming in the model more than
compensates the warming in the tropical Pacific that develops in the
4 <span class="inline-formula">×</span> CO<span class="inline-formula"><sub>2</sub></span> scenario. We see an overcooling of 0.3 <span class="inline-formula"><sup>∘</sup></span>C and a
0.23 mm d<span class="inline-formula"><sup>−1</sup></span> (5 %) reduction in mean rainfall over the tropical Pacific
relative to preindustrial conditions in the G1 simulation, owing to the
different latitudinal distributions of the shortwave (solar) and longwave
(CO<span class="inline-formula"><sub>2</sub></span>) forcings. The location of the Intertropical Convergence Zone
(ITCZ) in the tropical Pacific, which moved 7.5<span class="inline-formula"><sup>∘</sup></span> southwards under
4 <span class="inline-formula">×</span> CO<span class="inline-formula"><sub>2</sub></span>, is restored to its preindustrial position. However,
other aspects of the tropical Pacific mean climate are not reset as
effectively. Relative to preindustrial conditions, in G1 the time-averaged
zonal wind stress, zonal sea surface temperature (SST) gradient, and
meridional SST gradient are each statistically significantly reduced by
around 10 %, and the Pacific Walker Circulation (PWC) is consistently
weakened, resulting in conditions conducive to increased frequency of El
Niño events. The overall amplitude of ENSO strengthens by 9 %–10 % in
G1, but there is a 65 % reduction in the asymmetry between cold and warm
events: cold events intensify more than warm events. Notably, the frequency
of extreme El Niño and La Niña events increases by ca. 60 % and
30 %, respectively, while the total number of El Niño events increases
by around 10 %. All of these changes are statistically significant at either 95 or 99 % confidence level. Somewhat paradoxically, while the number
of total and extreme events increases, the extreme El Niño events become
weaker relative to the preindustrial state, while the extreme La Niña
events become even stronger. That is, such extreme El Niño events in G1
become less intense than under preindustrial conditions but also more
frequent. In contrast, extreme La Niña events become stronger in G1,
which is in agreement with the general overcooling of the tropical Pacific
in G1 relative to preindustrial conditions.</p> |
| first_indexed | 2024-12-22T20:25:35Z |
| format | Article |
| id | doaj.art-3fff6ac4dd7b49688f9d7a9237ab5650 |
| institution | Directory Open Access Journal |
| issn | 1680-7316 1680-7324 |
| language | English |
| last_indexed | 2024-12-22T20:25:35Z |
| publishDate | 2020-12-01 |
| publisher | Copernicus Publications |
| record_format | Article |
| series | Atmospheric Chemistry and Physics |
| spelling | doaj.art-3fff6ac4dd7b49688f9d7a9237ab56502022-12-21T18:13:44ZengCopernicus PublicationsAtmospheric Chemistry and Physics1680-73161680-73242020-12-0120154611548510.5194/acp-20-15461-2020Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremesA. Malik0A. Malik1A. Malik2P. J. Nowack3P. J. Nowack4P. J. Nowack5P. J. Nowack6J. D. Haigh7J. D. Haigh8L. Cao9L. Atique10Y. Plancherel11Grantham Institute – Climate Change and the Environment, Imperial College London, London, United KingdomOeschger Centre for Climate Change Research and Institute of Geography, University of Bern, Bern, SwitzerlandKing Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi ArabiaGrantham Institute – Climate Change and the Environment, Imperial College London, London, United KingdomBlackett Laboratory, Department of Physics, Imperial College London, London, United KingdomData Science Institute, Imperial College London, London, United KingdomSchool of Environmental Sciences, University of East Anglia, Norwich, United KingdomGrantham Institute – Climate Change and the Environment, Imperial College London, London, United KingdomBlackett Laboratory, Department of Physics, Imperial College London, London, United KingdomSchool of Earth Sciences, Zhejiang University, Hangzhou, ChinaSchool of Earth Sciences, Zhejiang University, Hangzhou, ChinaGrantham Institute – Climate Change and the Environment, Imperial College London, London, United Kingdom<p>Many modelling studies suggest that the El Niño–Southern Oscillation (ENSO), in interaction with the tropical Pacific background climate, will change with rising atmospheric greenhouse gas concentrations. Solar geoengineering (reducing the solar flux from outer space) has been proposed as a means to counteract anthropogenic climate change. However, the effectiveness of solar geoengineering concerning a variety of aspects of Earth's climate is uncertain. Robust results are particularly challenging to obtain for ENSO because existing geoengineering simulations are too short (typically <span class="inline-formula">∼</span> 50 years) to detect statistically significant changes in the highly variable tropical Pacific background climate. We here present results from a 1000-year-long solar-geoengineering simulation, G1, carried out with the coupled atmosphere–ocean general circulation model HadCM3L. In agreement with previous studies, reducing the solar irradiance (4 %) to offset global mean surface warming in the model more than compensates the warming in the tropical Pacific that develops in the 4 <span class="inline-formula">×</span> CO<span class="inline-formula"><sub>2</sub></span> scenario. We see an overcooling of 0.3 <span class="inline-formula"><sup>∘</sup></span>C and a 0.23 mm d<span class="inline-formula"><sup>−1</sup></span> (5 %) reduction in mean rainfall over the tropical Pacific relative to preindustrial conditions in the G1 simulation, owing to the different latitudinal distributions of the shortwave (solar) and longwave (CO<span class="inline-formula"><sub>2</sub></span>) forcings. The location of the Intertropical Convergence Zone (ITCZ) in the tropical Pacific, which moved 7.5<span class="inline-formula"><sup>∘</sup></span> southwards under 4 <span class="inline-formula">×</span> CO<span class="inline-formula"><sub>2</sub></span>, is restored to its preindustrial position. However, other aspects of the tropical Pacific mean climate are not reset as effectively. Relative to preindustrial conditions, in G1 the time-averaged zonal wind stress, zonal sea surface temperature (SST) gradient, and meridional SST gradient are each statistically significantly reduced by around 10 %, and the Pacific Walker Circulation (PWC) is consistently weakened, resulting in conditions conducive to increased frequency of El Niño events. The overall amplitude of ENSO strengthens by 9 %–10 % in G1, but there is a 65 % reduction in the asymmetry between cold and warm events: cold events intensify more than warm events. Notably, the frequency of extreme El Niño and La Niña events increases by ca. 60 % and 30 %, respectively, while the total number of El Niño events increases by around 10 %. All of these changes are statistically significant at either 95 or 99 % confidence level. Somewhat paradoxically, while the number of total and extreme events increases, the extreme El Niño events become weaker relative to the preindustrial state, while the extreme La Niña events become even stronger. That is, such extreme El Niño events in G1 become less intense than under preindustrial conditions but also more frequent. In contrast, extreme La Niña events become stronger in G1, which is in agreement with the general overcooling of the tropical Pacific in G1 relative to preindustrial conditions.</p>https://acp.copernicus.org/articles/20/15461/2020/acp-20-15461-2020.pdf |
| spellingShingle | A. Malik A. Malik A. Malik P. J. Nowack P. J. Nowack P. J. Nowack P. J. Nowack J. D. Haigh J. D. Haigh L. Cao L. Atique Y. Plancherel Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes Atmospheric Chemistry and Physics |
| title | Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes |
| title_full | Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes |
| title_fullStr | Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes |
| title_full_unstemmed | Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes |
| title_short | Tropical Pacific climate variability under solar geoengineering: impacts on ENSO extremes |
| title_sort | tropical pacific climate variability under solar geoengineering impacts on enso extremes |
| url | https://acp.copernicus.org/articles/20/15461/2020/acp-20-15461-2020.pdf |
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