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Miocene climate modelling sensitivity experiments ABSTRACTThroughout the Cenozoic the global climate cooled, but until the Pliocene, temperatures in polar regions seem to have been higher than at present, and it is not yet clear if the Arctic Ocean was already ice-covered in the Miocene. Reconstructions for Miocene atmospheric carbon dioxide concentration do not give a coherent climatic picture: intervals of ice-free conditions in the Arctic region appear to correspond to low CO2, and intervals during which the Arctic Ocean was ice-covered had high CO2 levels. Here we present the results of climate modelling sensitivity experiments for the Late Miocene, considering different CO2 concentrations. In order to get ice-free conditions in the Arctic Ocean, a CO2 concentration of at least 1500 ppm is necessary. Concentrations this high are unlikely for the Miocene, and our results support onset of Northern Hemisphere glaciation earlier than Late Miocene. Compared to future climate change scenarios with enhanced CO2, the modelled temperature response to CO2 increase is slightly weaker in our Miocene sensitivity experiments. This dampened response is due to the decreased sea ice volume in the Miocene and the reduced ice-albedo feedback. Comparing our sensitivity experiments with quantitative terrestrial proxy data to give an estimation for pCO2 in the Late Miocene we find that model runs with 360 ppm and 460 ppm are most consistent with proxy data. This validation thus suggests that Late Miocene CO2 concentrations were higher than present but lower than 500 ppm. Keywords: Miocene, Late; climate modelling; sensitivity experiment; CO2; proxy data comparison
PE Article Number: 12.2.5A |
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