Cretaceous Simulation with the Earth System Model AWI-ESM-2


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Christian.Stepanek [ at ] awi.de

Abstract

The Earth’s climate during the Cretaceous period was characterized by temperatures warmer than today driven by a high CO2 level. Due to the continuous rise in our atmospheric CO2 concentration since the Industrial Revolution, Cretaceous climate is now of particular interest as a suitable analog to our future climate changes. Here, the Cretaceous climate has been investigated using the newly developed AWI-Earth System Model 2 (AWI-ESM-2) with interactive vegetation at different CO2 concentrations. The AWI-ESM-2 employs coupled sub-models of FESOM with unstructured mesh, the ECHAM running on T63 grid and a land surface scheme with interactive vegetation dynamics to produce a reasonable representation of Cretaceous climate and vegetation. The atmospheric CO2 concentrations of 1x, 4x, 6x the PI value (280ppm) with other greenhouse gases (N2O and CH4) fixed at PI levels were used to run three modeling experiments. Results obtained indicated a warmer surface temperature and vanishing of sea ice cover at the two higher CO2 experiments, with the Antarctic summer temperature as warm as 23 °C and a completely ice free Antarctic continent at the CR_6x simulation. At both CR_4x and CR_6x simulations, snow presence was seasonally dependent, with up to 25 cm snow present in the high latitudes at both Austral and Boreal winter, indicating seasonal dependency. The tropics were generally wetter, most especially the summer of CR_6x, while the precipitation level of Antarctica appears similar. Also, the Antarctic mid-Cretaceous terrestrial ecosystem seems to be sensitive to CO2 changes, as the coniferous evergreen forest dominated continent during the CR_1x simulation shifted to a mix of coniferous and extra-tropical evergreen trees under both CR_4x and CR_6x. Additionally, comparing PI and mid-Cretaceous simulations at 280 ppmv and 1120 ppmv shows that CR_4x has an average surface temperature much warmer than PI_4x, especially towards the South Pole. These findings are consistent with the idea that a temperate climate in the high latitude of mid-Cretaceous period requires high CO2 forcing and that permanent ice cannot survive towards the South Pole with an elevated CO2. The interactive vegetation approach also confirms the influence of important feedbacks particularly over ice free Antarctica.



Item Type
Thesis (Master)
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Helmholtz Cross Cutting Activity (2021-2027)
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Not peer-reviewed
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Published
Eprint ID
55844
Cite as
Gidado, K. T. (2022): Cretaceous Simulation with the Earth System Model AWI-ESM-2 , Master thesis, Alfred Wegener Institute.


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