On the state dependency of 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 CO2 proxy data together with a 3-D ice-s...
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COPERNICUS GESELLSCHAFT MBH
2015
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Online Access: | https://epic.awi.de/id/eprint/39311/ https://epic.awi.de/id/eprint/39311/1/koehler2015cp.pdf http://www.clim-past.net/11/1801/2015/ https://hdl.handle.net/10013/epic.46498 https://hdl.handle.net/10013/epic.46498.d001 |
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ftawi:oai:epic.awi.de:39311 2023-05-15T16:40:55+02:00 On the state dependency of equilibrium climate sensitivity during the last 5 million years Köhler, Peter de Boer, Bas von der Heydt, Anna S. Stap, Lennart S. van de Wal, Roderik S. W. 2015 application/pdf https://epic.awi.de/id/eprint/39311/ https://epic.awi.de/id/eprint/39311/1/koehler2015cp.pdf http://www.clim-past.net/11/1801/2015/ https://hdl.handle.net/10013/epic.46498 https://hdl.handle.net/10013/epic.46498.d001 unknown COPERNICUS GESELLSCHAFT MBH https://epic.awi.de/id/eprint/39311/1/koehler2015cp.pdf https://hdl.handle.net/10013/epic.46498.d001 Köhler, P. orcid:0000-0003-0904-8484 , de Boer, B. , von der Heydt, A. S. , Stap, L. S. and van de Wal, R. S. W. (2015) On the state dependency of equilibrium climate sensitivity during the last 5 million years , Climate of the Past, 11 , pp. 1801-1823 . doi:10.5194/cp-11-1801-2015 <https://doi.org/10.5194/cp-11-1801-2015> , hdl:10013/epic.46498 EPIC3Climate of the Past, COPERNICUS GESELLSCHAFT MBH, 11, pp. 1801-1823, ISSN: 1814-9324 Article isiRev 2015 ftawi https://doi.org/10.5194/cp-11-1801-2015 2021-12-24T15:40:57Z 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 CO2 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 CO2 radiative forcing depends on the CO2 data set used. This nonlinearity 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 icesheet 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 CO2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, STCO2,LIU, for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, STCO2,LIU is on average � 45% larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 MyrBP) the CO2 data uncertainties prevent a well-supported calculation for STCO2,LIU, but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 MyrBP), the specific equilibrium climate sensitivity, STCO2,LIU, 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 CO2 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. Article in Journal/Newspaper Ice Sheet Alfred Wegener Institute for Polar- and Marine Research (AWI): ePIC (electronic Publication Information Center) Climate of the Past 11 12 1801 1823 |
institution |
Open Polar |
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Alfred Wegener Institute for Polar- and Marine Research (AWI): ePIC (electronic Publication Information Center) |
op_collection_id |
ftawi |
language |
unknown |
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 CO2 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 CO2 radiative forcing depends on the CO2 data set used. This nonlinearity 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 icesheet 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 CO2 and of the land ice albedo (LI) is combined, we find a state dependence in the calculated specific equilibrium climate sensitivity, STCO2,LIU, for most of the Pleistocene (last 2.1 Myr). During Pleistocene intermediate glaciated climates and interglacial periods, STCO2,LIU is on average � 45% larger than during Pleistocene full glacial conditions. In the Pliocene part of our analysis (2.6–5 MyrBP) the CO2 data uncertainties prevent a well-supported calculation for STCO2,LIU, but our analysis suggests that during times without a large land ice area in the Northern Hemisphere (e.g. before 2.82 MyrBP), the specific equilibrium climate sensitivity, STCO2,LIU, 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 CO2 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 |
Article in Journal/Newspaper |
author |
Köhler, Peter de Boer, Bas von der Heydt, Anna S. Stap, Lennart S. van de Wal, Roderik S. W. |
spellingShingle |
Köhler, Peter de Boer, Bas von der Heydt, Anna S. Stap, Lennart S. van de Wal, Roderik S. W. On the state dependency of equilibrium climate sensitivity during the last 5 million years |
author_facet |
Köhler, Peter de Boer, Bas von der Heydt, Anna S. Stap, Lennart S. van de Wal, Roderik S. W. |
author_sort |
Köhler, Peter |
title |
On the state dependency of equilibrium climate sensitivity during the last 5 million years |
title_short |
On the state dependency of equilibrium climate sensitivity during the last 5 million years |
title_full |
On the state dependency of equilibrium climate sensitivity during the last 5 million years |
title_fullStr |
On the state dependency of equilibrium climate sensitivity during the last 5 million years |
title_full_unstemmed |
On the state dependency of equilibrium climate sensitivity during the last 5 million years |
title_sort |
on the state dependency of equilibrium climate sensitivity during the last 5 million years |
publisher |
COPERNICUS GESELLSCHAFT MBH |
publishDate |
2015 |
url |
https://epic.awi.de/id/eprint/39311/ https://epic.awi.de/id/eprint/39311/1/koehler2015cp.pdf http://www.clim-past.net/11/1801/2015/ https://hdl.handle.net/10013/epic.46498 https://hdl.handle.net/10013/epic.46498.d001 |
genre |
Ice Sheet |
genre_facet |
Ice Sheet |
op_source |
EPIC3Climate of the Past, COPERNICUS GESELLSCHAFT MBH, 11, pp. 1801-1823, ISSN: 1814-9324 |
op_relation |
https://epic.awi.de/id/eprint/39311/1/koehler2015cp.pdf https://hdl.handle.net/10013/epic.46498.d001 Köhler, P. orcid:0000-0003-0904-8484 , de Boer, B. , von der Heydt, A. S. , Stap, L. S. and van de Wal, R. S. W. (2015) On the state dependency of equilibrium climate sensitivity during the last 5 million years , Climate of the Past, 11 , pp. 1801-1823 . doi:10.5194/cp-11-1801-2015 <https://doi.org/10.5194/cp-11-1801-2015> , hdl:10013/epic.46498 |
op_doi |
https://doi.org/10.5194/cp-11-1801-2015 |
container_title |
Climate of the Past |
container_volume |
11 |
container_issue |
12 |
container_start_page |
1801 |
op_container_end_page |
1823 |
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1766031343478636544 |