The hemispheric contrast in cloud microphysical properties constrains aerosol forcing
The change in planetary albedo due to aerosol−cloud interactions during the industrial era is the leading source of uncertainty in inferring Earth’s climate sensitivity to increased greenhouse gases from the historical record. The variable that controls aerosol−cloud interactions in warm clouds is d...
Published in: | Proceedings of the National Academy of Sciences |
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National Academy of Sciences
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Online Access: | https://doi.org/10.1073/pnas.1922502117 https://ora.ox.ac.uk/objects/uuid:0b7ed106-0479-4cde-bca1-81eb36cf7f5b |
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ftuloxford:oai:ora.ox.ac.uk:uuid:0b7ed106-0479-4cde-bca1-81eb36cf7f5b 2024-10-06T13:42:44+00:00 The hemispheric contrast in cloud microphysical properties constrains aerosol forcing McCoy, IL McCoy, D Wood, R Regayre, L Watson-Parris, D Grosvenor, DP Mulcahy, JP Hu, Y Bender, FAM Field, PR Carslaw, KS Gordon, H 2020-06-24 https://doi.org/10.1073/pnas.1922502117 https://ora.ox.ac.uk/objects/uuid:0b7ed106-0479-4cde-bca1-81eb36cf7f5b eng eng National Academy of Sciences doi:10.1073/pnas.1922502117 https://ora.ox.ac.uk/objects/uuid:0b7ed106-0479-4cde-bca1-81eb36cf7f5b https://doi.org/10.1073/pnas.1922502117 info:eu-repo/semantics/openAccess CC Attribution (CC BY) Journal article 2020 ftuloxford https://doi.org/10.1073/pnas.1922502117 2024-09-06T07:47:27Z The change in planetary albedo due to aerosol−cloud interactions during the industrial era is the leading source of uncertainty in inferring Earth’s climate sensitivity to increased greenhouse gases from the historical record. The variable that controls aerosol−cloud interactions in warm clouds is droplet number concentration. Global climate models demonstrate that the present-day hemispheric contrast in cloud droplet number concentration between the pristine Southern Hemisphere and the polluted Northern Hemisphere oceans can be used as a proxy for anthropogenically driven change in cloud droplet number concentration. Remotely sensed estimates constrain this change in droplet number concentration to be between 8 cm−3 and 24 cm−3. By extension, the radiative forcing since 1850 from aerosol−cloud interactions is constrained to be −1.2 W⋅m−2 to −0.6 W⋅m−2. The robustness of this constraint depends upon the assumption that pristine Southern Ocean droplet number concentration is a suitable proxy for preindustrial concentrations. Droplet number concentrations calculated from satellite data over the Southern Ocean are high in austral summer. Near Antarctica, they reach values typical of Northern Hemisphere polluted outflows. These concentrations are found to agree with several in situ datasets. In contrast, climate models show systematic underpredictions of cloud droplet number concentration across the Southern Ocean. Near Antarctica, where precipitation sinks of aerosol are small, the underestimation by climate models is particularly large. This motivates the need for detailed process studies of aerosol production and aerosol−cloud interactions in pristine environments. The hemispheric difference in satellite estimated cloud droplet number concentration implies preindustrial aerosol concentrations were higher than estimated by most models. Article in Journal/Newspaper Antarc* Antarctica Southern Ocean ORA - Oxford University Research Archive Austral Southern Ocean Proceedings of the National Academy of Sciences 117 32 18998 19006 |
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Open Polar |
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ORA - Oxford University Research Archive |
op_collection_id |
ftuloxford |
language |
English |
description |
The change in planetary albedo due to aerosol−cloud interactions during the industrial era is the leading source of uncertainty in inferring Earth’s climate sensitivity to increased greenhouse gases from the historical record. The variable that controls aerosol−cloud interactions in warm clouds is droplet number concentration. Global climate models demonstrate that the present-day hemispheric contrast in cloud droplet number concentration between the pristine Southern Hemisphere and the polluted Northern Hemisphere oceans can be used as a proxy for anthropogenically driven change in cloud droplet number concentration. Remotely sensed estimates constrain this change in droplet number concentration to be between 8 cm−3 and 24 cm−3. By extension, the radiative forcing since 1850 from aerosol−cloud interactions is constrained to be −1.2 W⋅m−2 to −0.6 W⋅m−2. The robustness of this constraint depends upon the assumption that pristine Southern Ocean droplet number concentration is a suitable proxy for preindustrial concentrations. Droplet number concentrations calculated from satellite data over the Southern Ocean are high in austral summer. Near Antarctica, they reach values typical of Northern Hemisphere polluted outflows. These concentrations are found to agree with several in situ datasets. In contrast, climate models show systematic underpredictions of cloud droplet number concentration across the Southern Ocean. Near Antarctica, where precipitation sinks of aerosol are small, the underestimation by climate models is particularly large. This motivates the need for detailed process studies of aerosol production and aerosol−cloud interactions in pristine environments. The hemispheric difference in satellite estimated cloud droplet number concentration implies preindustrial aerosol concentrations were higher than estimated by most models. |
format |
Article in Journal/Newspaper |
author |
McCoy, IL McCoy, D Wood, R Regayre, L Watson-Parris, D Grosvenor, DP Mulcahy, JP Hu, Y Bender, FAM Field, PR Carslaw, KS Gordon, H |
spellingShingle |
McCoy, IL McCoy, D Wood, R Regayre, L Watson-Parris, D Grosvenor, DP Mulcahy, JP Hu, Y Bender, FAM Field, PR Carslaw, KS Gordon, H The hemispheric contrast in cloud microphysical properties constrains aerosol forcing |
author_facet |
McCoy, IL McCoy, D Wood, R Regayre, L Watson-Parris, D Grosvenor, DP Mulcahy, JP Hu, Y Bender, FAM Field, PR Carslaw, KS Gordon, H |
author_sort |
McCoy, IL |
title |
The hemispheric contrast in cloud microphysical properties constrains aerosol forcing |
title_short |
The hemispheric contrast in cloud microphysical properties constrains aerosol forcing |
title_full |
The hemispheric contrast in cloud microphysical properties constrains aerosol forcing |
title_fullStr |
The hemispheric contrast in cloud microphysical properties constrains aerosol forcing |
title_full_unstemmed |
The hemispheric contrast in cloud microphysical properties constrains aerosol forcing |
title_sort |
hemispheric contrast in cloud microphysical properties constrains aerosol forcing |
publisher |
National Academy of Sciences |
publishDate |
2020 |
url |
https://doi.org/10.1073/pnas.1922502117 https://ora.ox.ac.uk/objects/uuid:0b7ed106-0479-4cde-bca1-81eb36cf7f5b |
geographic |
Austral Southern Ocean |
geographic_facet |
Austral Southern Ocean |
genre |
Antarc* Antarctica Southern Ocean |
genre_facet |
Antarc* Antarctica Southern Ocean |
op_relation |
doi:10.1073/pnas.1922502117 https://ora.ox.ac.uk/objects/uuid:0b7ed106-0479-4cde-bca1-81eb36cf7f5b https://doi.org/10.1073/pnas.1922502117 |
op_rights |
info:eu-repo/semantics/openAccess CC Attribution (CC BY) |
op_doi |
https://doi.org/10.1073/pnas.1922502117 |
container_title |
Proceedings of the National Academy of Sciences |
container_volume |
117 |
container_issue |
32 |
container_start_page |
18998 |
op_container_end_page |
19006 |
_version_ |
1812176921520242688 |