On the climate sensitivity and historical warming evolution in recent coupled model ensembles
The Earth's equilibrium climate sensitivity (ECS) to a doubling of atmospheric CO 2 , along with the transient climate response (TCR) and greenhouse gas emissions pathways, determines the amount of future warming. Coupled climate models have in the past been important tools to estimate and unde...
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ftdoajarticles:oai:doaj.org/article:f8df15dddb74434a83137b7abd878971 2023-05-15T13:57:11+02:00 On the climate sensitivity and historical warming evolution in recent coupled model ensembles C. M. Flynn T. Mauritsen 2020-07-01T00:00:00Z https://doi.org/10.5194/acp-20-7829-2020 https://doaj.org/article/f8df15dddb74434a83137b7abd878971 EN eng Copernicus Publications https://www.atmos-chem-phys.net/20/7829/2020/acp-20-7829-2020.pdf https://doaj.org/toc/1680-7316 https://doaj.org/toc/1680-7324 doi:10.5194/acp-20-7829-2020 1680-7316 1680-7324 https://doaj.org/article/f8df15dddb74434a83137b7abd878971 Atmospheric Chemistry and Physics, Vol 20, Pp 7829-7842 (2020) Physics QC1-999 Chemistry QD1-999 article 2020 ftdoajarticles https://doi.org/10.5194/acp-20-7829-2020 2022-12-31T14:21:36Z The Earth's equilibrium climate sensitivity (ECS) to a doubling of atmospheric CO 2 , along with the transient climate response (TCR) and greenhouse gas emissions pathways, determines the amount of future warming. Coupled climate models have in the past been important tools to estimate and understand ECS. ECS estimated from Coupled Model Intercomparison Project Phase 5 (CMIP5) models lies between 2.0 and 4.7 K (mean of 3.2 K ), whereas in the latest CMIP6 the spread has increased to 1.8–5.5 K (mean of 3.7 K ), with 5 out of 25 models exceeding 5 K . It is thus pertinent to understand the causes underlying this shift. Here we compare the CMIP5 and CMIP6 model ensembles and find a systematic shift between CMIP eras to be unexplained as a process of random sampling from modeled forcing and feedback distributions. Instead, shortwave feedbacks shift towards more positive values, in particular over the Southern Ocean, driving the shift towards larger ECS values in many of the models. These results suggest that changes in model treatment of mixed-phase cloud processes and changes to Antarctic sea ice representation are likely causes of the shift towards larger ECS. Somewhat surprisingly, CMIP6 models exhibit less historical warming than CMIP5 models, despite an increase in TCR between CMIP eras (mean TCR increased from 1.7 to 1.9 K ). The evolution of the warming suggests, however, that several of the CMIP6 models apply too strong aerosol cooling, resulting in too weak mid-20th century warming compared to the instrumental record. Article in Journal/Newspaper Antarc* Antarctic Sea ice Southern Ocean Directory of Open Access Journals: DOAJ Articles Antarctic Southern Ocean Atmospheric Chemistry and Physics 20 13 7829 7842 |
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Open Polar |
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Directory of Open Access Journals: DOAJ Articles |
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ftdoajarticles |
language |
English |
topic |
Physics QC1-999 Chemistry QD1-999 |
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Physics QC1-999 Chemistry QD1-999 C. M. Flynn T. Mauritsen On the climate sensitivity and historical warming evolution in recent coupled model ensembles |
topic_facet |
Physics QC1-999 Chemistry QD1-999 |
description |
The Earth's equilibrium climate sensitivity (ECS) to a doubling of atmospheric CO 2 , along with the transient climate response (TCR) and greenhouse gas emissions pathways, determines the amount of future warming. Coupled climate models have in the past been important tools to estimate and understand ECS. ECS estimated from Coupled Model Intercomparison Project Phase 5 (CMIP5) models lies between 2.0 and 4.7 K (mean of 3.2 K ), whereas in the latest CMIP6 the spread has increased to 1.8–5.5 K (mean of 3.7 K ), with 5 out of 25 models exceeding 5 K . It is thus pertinent to understand the causes underlying this shift. Here we compare the CMIP5 and CMIP6 model ensembles and find a systematic shift between CMIP eras to be unexplained as a process of random sampling from modeled forcing and feedback distributions. Instead, shortwave feedbacks shift towards more positive values, in particular over the Southern Ocean, driving the shift towards larger ECS values in many of the models. These results suggest that changes in model treatment of mixed-phase cloud processes and changes to Antarctic sea ice representation are likely causes of the shift towards larger ECS. Somewhat surprisingly, CMIP6 models exhibit less historical warming than CMIP5 models, despite an increase in TCR between CMIP eras (mean TCR increased from 1.7 to 1.9 K ). The evolution of the warming suggests, however, that several of the CMIP6 models apply too strong aerosol cooling, resulting in too weak mid-20th century warming compared to the instrumental record. |
format |
Article in Journal/Newspaper |
author |
C. M. Flynn T. Mauritsen |
author_facet |
C. M. Flynn T. Mauritsen |
author_sort |
C. M. Flynn |
title |
On the climate sensitivity and historical warming evolution in recent coupled model ensembles |
title_short |
On the climate sensitivity and historical warming evolution in recent coupled model ensembles |
title_full |
On the climate sensitivity and historical warming evolution in recent coupled model ensembles |
title_fullStr |
On the climate sensitivity and historical warming evolution in recent coupled model ensembles |
title_full_unstemmed |
On the climate sensitivity and historical warming evolution in recent coupled model ensembles |
title_sort |
on the climate sensitivity and historical warming evolution in recent coupled model ensembles |
publisher |
Copernicus Publications |
publishDate |
2020 |
url |
https://doi.org/10.5194/acp-20-7829-2020 https://doaj.org/article/f8df15dddb74434a83137b7abd878971 |
geographic |
Antarctic Southern Ocean |
geographic_facet |
Antarctic Southern Ocean |
genre |
Antarc* Antarctic Sea ice Southern Ocean |
genre_facet |
Antarc* Antarctic Sea ice Southern Ocean |
op_source |
Atmospheric Chemistry and Physics, Vol 20, Pp 7829-7842 (2020) |
op_relation |
https://www.atmos-chem-phys.net/20/7829/2020/acp-20-7829-2020.pdf https://doaj.org/toc/1680-7316 https://doaj.org/toc/1680-7324 doi:10.5194/acp-20-7829-2020 1680-7316 1680-7324 https://doaj.org/article/f8df15dddb74434a83137b7abd878971 |
op_doi |
https://doi.org/10.5194/acp-20-7829-2020 |
container_title |
Atmospheric Chemistry and Physics |
container_volume |
20 |
container_issue |
13 |
container_start_page |
7829 |
op_container_end_page |
7842 |
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