On the state dependency of the equilibrium climate sensitivity during the last 5 million years
It is still an open question how equilibrium warming in response to increasing radiative forcing – the specific equilibrium climate sensitivity S – depends on background climate. We here present palaeodata-based evidence on the state dependency of S , by using CO 2 proxy data together with a 3-D ice...
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ftcopernicus:oai:publications.copernicus.org:cp30746 2023-05-15T16:40:38+02:00 On the state dependency of the equilibrium climate sensitivity during the last 5 million years Köhler, P. Boer, B. Heydt, A. S. Stap, L. B. Wal, R. S. W. 2018-09-27 application/pdf https://doi.org/10.5194/cp-11-1801-2015 https://cp.copernicus.org/articles/11/1801/2015/ eng eng doi:10.5194/cp-11-1801-2015 https://cp.copernicus.org/articles/11/1801/2015/ eISSN: 1814-9332 Text 2018 ftcopernicus https://doi.org/10.5194/cp-11-1801-2015 2020-07-20T16:24:20Z It is still an open question how equilibrium warming in response to increasing radiative forcing – the specific equilibrium climate sensitivity S – depends on background climate. We here present palaeodata-based evidence on the state dependency of S , by using CO 2 proxy data together with a 3-D ice-sheet-model-based reconstruction of land ice albedo over the last 5 million years (Myr). We find that the land ice albedo forcing depends non-linearly on the background climate, while any non-linearity of CO 2 radiative forcing depends on the CO 2 data set used. This non-linearity has not, so far, been accounted for in similar approaches due to previously more simplistic approximations, in which land ice albedo radiative forcing was a linear function of sea level change. The latitudinal dependency of ice-sheet area changes is important for the non-linearity between land ice albedo and sea level. In our set-up, in which the radiative forcing of CO 2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, S [CO 2 ,LI] , for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, S [CO 2 ,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 Myr BP) the CO 2 data uncertainties prevent a well-supported calculation for S [CO 2 ,LI] , but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 Myr BP), the specific equilibrium climate sensitivity, S [CO 2 ,LI] , was smaller than during interglacials of the Pleistocene. We thus find support for a previously proposed state change in the climate system with the widespread appearance of northern hemispheric ice sheets. This study points for the first time to a so far overlooked non-linearity in the land ice albedo radiative forcing, which is important for similar palaeodata-based approaches to calculate climate sensitivity. However, the implications of this study for a suggested warming under CO 2 doubling are not yet entirely clear since the details of necessary corrections for other slow feedbacks are not fully known and the uncertainties that exist in the ice-sheet simulations and global temperature reconstructions are large. Text Ice Sheet Copernicus Publications: E-Journals Climate of the Past 11 12 1801 1823 |
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Open Polar |
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Copernicus Publications: E-Journals |
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ftcopernicus |
language |
English |
description |
It is still an open question how equilibrium warming in response to increasing radiative forcing – the specific equilibrium climate sensitivity S – depends on background climate. We here present palaeodata-based evidence on the state dependency of S , by using CO 2 proxy data together with a 3-D ice-sheet-model-based reconstruction of land ice albedo over the last 5 million years (Myr). We find that the land ice albedo forcing depends non-linearly on the background climate, while any non-linearity of CO 2 radiative forcing depends on the CO 2 data set used. This non-linearity has not, so far, been accounted for in similar approaches due to previously more simplistic approximations, in which land ice albedo radiative forcing was a linear function of sea level change. The latitudinal dependency of ice-sheet area changes is important for the non-linearity between land ice albedo and sea level. In our set-up, in which the radiative forcing of CO 2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, S [CO 2 ,LI] , for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, S [CO 2 ,LI] is on average ~ 45 % larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 Myr BP) the CO 2 data uncertainties prevent a well-supported calculation for S [CO 2 ,LI] , but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 Myr BP), the specific equilibrium climate sensitivity, S [CO 2 ,LI] , was smaller than during interglacials of the Pleistocene. We thus find support for a previously proposed state change in the climate system with the widespread appearance of northern hemispheric ice sheets. This study points for the first time to a so far overlooked non-linearity in the land ice albedo radiative forcing, which is important for similar palaeodata-based approaches to calculate climate sensitivity. However, the implications of this study for a suggested warming under CO 2 doubling are not yet entirely clear since the details of necessary corrections for other slow feedbacks are not fully known and the uncertainties that exist in the ice-sheet simulations and global temperature reconstructions are large. |
format |
Text |
author |
Köhler, P. Boer, B. Heydt, A. S. Stap, L. B. Wal, R. S. W. |
spellingShingle |
Köhler, P. Boer, B. Heydt, A. S. Stap, L. B. Wal, R. S. W. On the state dependency of the equilibrium climate sensitivity during the last 5 million years |
author_facet |
Köhler, P. Boer, B. Heydt, A. S. Stap, L. B. Wal, R. S. W. |
author_sort |
Köhler, P. |
title |
On the state dependency of the equilibrium climate sensitivity during the last 5 million years |
title_short |
On the state dependency of the equilibrium climate sensitivity during the last 5 million years |
title_full |
On the state dependency of the equilibrium climate sensitivity during the last 5 million years |
title_fullStr |
On the state dependency of the equilibrium climate sensitivity during the last 5 million years |
title_full_unstemmed |
On the state dependency of the equilibrium climate sensitivity during the last 5 million years |
title_sort |
on the state dependency of the equilibrium climate sensitivity during the last 5 million years |
publishDate |
2018 |
url |
https://doi.org/10.5194/cp-11-1801-2015 https://cp.copernicus.org/articles/11/1801/2015/ |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_source |
eISSN: 1814-9332 |
op_relation |
doi:10.5194/cp-11-1801-2015 https://cp.copernicus.org/articles/11/1801/2015/ |
op_doi |
https://doi.org/10.5194/cp-11-1801-2015 |
container_title |
Climate of the Past |
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11 |
container_issue |
12 |
container_start_page |
1801 |
op_container_end_page |
1823 |
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1766031033813172224 |