The Early Eocene equable climate problem: can perturbations of climate model parameters identify possible solutions?
Geological data for the Early Eocene (5647.8Ma) indicate extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable datamodel differences in the prediction of these polar surface temperatures, resulting in the...
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Published in | Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences Vol. 371; no. 2001; p. 20130123 |
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Main Authors | , , , |
Format | Journal Article |
Language | English |
Published |
England
The Royal Society Publishing
28.10.2013
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Subjects | |
Online Access | Get full text |
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Summary: | Geological data for the Early Eocene (5647.8Ma) indicate extensive global warming, with very warm temperatures at both poles. However, despite numerous attempts to simulate this warmth, there are remarkable datamodel differences in the prediction of these polar surface temperatures, resulting in the so-called equable climate problem. In this paper, for the first time an ensemble with a perturbed climate-sensitive model parameters approach has been applied to modelling the Early Eocene climate. We performed more than 100 simulations with perturbed physics parameters, and identified two simulations that have an optimal fit with the proxy data. We have simulated the warmth of the Early Eocene at 560ppmv CO2, which is a much lower CO2 level than many other models. We investigate the changes in atmospheric circulation, cloud properties and ocean circulation that are common to these simulations and how they differ from the remaining simulations in order to understand what mechanisms contribute to the polar warming. The parameter set from one of the optimal Early Eocene simulations also produces a favourable fit for the last glacial maximum boundary climate and outperforms the control parameter set for the present day. Although this does not prove that this model is correct, it is very encouraging that there is a parameter set that creates a climate model able to simulate well very different palaeoclimates and the present-day climate. Interestingly, to achieve the great warmth of the Early Eocene this version of the model does not have a strong future climate change Charney climate sensitivity. It produces a Charney climate sensitivity of 2.7C, whereas the mean value of the 18 models in the IPCC Fourth Assessment Report (AR4) is 3.26C0.69C. Thus, this value is within the range and below the mean of the models included in the AR4. |
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Bibliography: | ArticleID:rsta20130123 istex:34951BDE3E5E6C16BD3D89D295CF998855C1AEC8 href:rsta20130123.pdf ark:/67375/V84-VS6P402B-B Present address: School of Earth and Environment, University of Leeds, Woodhouse Lane, Leeds LS2 9JT, UK. Discussion Meeting Issue 'Warm climates of the past-a lesson for the future?' compiled and edited by Daniel J. Lunt, Harry Elderfield, Richard Pancost and Andy Ridgwell ObjectType-Article-1 SourceType-Scholarly Journals-1 ObjectType-Feature-2 content type line 23 |
ISSN: | 1364-503X 1471-2962 |
DOI: | 10.1098/rsta.2013.0123 |