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Title: Warm equable palaeoclimates, the role of general circulation model uncertainty in model-data mismatch
Author: Sagoo, Navjit
ISNI:       0000 0004 5922 4367
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2014
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Geological data for past extremely warm climates such as the early Eocene and the late Jurrasic 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". This work explores how climate model uncertainty may contribute to the simulation of equable climates. A number of simulations are conducted for the Eocene and the Late Jurassic climates, including perturbed physics ensembles (PPEs) for both time periods. Uncertain climate-sensitive parameters are perturbed in these PPEs in order to understand the range of climates that can be simulated with these methods. Simulations investigating the sensitivity of the Late Jurassic climate to uncertain boundary conditions (C02 concentrations; orbital configuration; orography and soil properties) have also been carried out. The Eocene and Jurassic PPEs simulate the most equable climates. Whilst the perturbed soil and orography simulations have a smaller climate response than the PPE simulations and are too cold compared to the proxy data. One early Eocene PPE simulation shows a good match with the available proxy data and has a large polar amplification. This well performing Eocene simulation also simulates the present day climate well and has a low value of climate sensitivity. The same parameter set also simulates the Late Jurassic climate well when compared with proxy data. The Late Jurassic PPE has a smaller range of climates than the Eocene PPE and most simulations in the Late Jurassic PPE have a good match with the proxy data. Variation in the Eocene PPE appears to be driven by differences in cloud properties which are a large source of uncertainty in constraining present day climate forcing The main findings of this work indicate that perturbed parameter ensembles (PPEs) for global palaeoclimate could play an important role in improving both palaeoclimate and present day simulations
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available