Abstract
The early Eocene (~56-48 million years ago) is
characterised by high CO2 estimates (1200-2500 ppmv) and
elevated global temperatures (~10 to 16°C higher than
modern). However, the response of the hydrological cycle during the
early Eocene is poorly constrained, especially in regions with sparse
data coverage (e.g. Africa). Here we present a study of African
hydroclimate during the early Eocene, as simulated by an ensemble of
state-of-the-art climate models in the Deep-time Model Intercomparison
Project (DeepMIP). A comparison between the DeepMIP pre-industrial
simulations and modern observations suggests that model biases are
model- and geographically dependent, however these biases are reduced in
the model ensemble mean. A comparison between the Eocene simulations and
the pre-industrial suggests that there is no obvious wetting or drying
trend as the CO2 increases. The results suggest that
changes to the land sea mask (relative to modern) in the models may be
responsible for the simulated increases in precipitation to the north of
Eocene Africa, whereas it is likely that changes in vegetation in the
models are responsible for the simulated region of drying over
equatorial Eocene Africa. There is an increase in precipitation over
equatorial and West Africa and associated drying over northern Africa as
CO2 rises. There are also important dynamical changes,
with evidence that anticyclonic low-level circulation is replaced by
increased south-westerly flow at high CO2 levels.
Lastly, a model-data comparison using newly-compiled quantitative
climate estimates from palaeobotanical proxy data suggests a marginally
better fit with the reconstructions at lower levels of CO2.