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Improvements on a simple model of the global carbon cycle

Corbyn, Sarah (2009) Improvements on a simple model of the global carbon cycle. Other thesis, Murdoch University.


This report describes improvements and changes made to a simple model of the global carbon cycle originally developed by Bice (2007). The model simulation period is from 1850 to 2000, and the steady state for atmospheric CO2 concentration changed from 280ppm in the original model to 285ppm in the improved model. The original model has 5 reservoirs: atmosphere, surface ocean, deep ocean, land biota and soil. An additional ‘earth’ reservoir is added to the improved model. These reservoirs have various fluxes between them, and all are assumed to have equally distributed carbon, analogous to ‘well-mixed tanks’.

Changes are made to the half-saturation value (effecting the Michaelis-Menten kinetics describing photosynthesis); and it is found that the temperature sensitivity of photosynthesis is best parameterised to reflect average measured land surface temperature of around 8oC. An improved method for accounting for anthropogenic changes due to burning of land biota is developed.

A global energy balance is incorporated into the model. This energy balance uses a ‘grey atmosphere’ approximation, as developed by Lenton (2000). Results of this energy model are in line with historical measured average global surface temperature (GST) anomalies from the Climate Research Unit (CRU) CRUTEM3 temperature dataset. However, it is shown that this energy model is somewhat unreliable, as the same ‘global warming’ effect can be reproduced by making small changes to planetary albedo, and possible changes to solar irradiation and relative humidity are not accounted for. Regardless of this, the energy model output for future predictions is in the same range as those made by the Intergovernmental Panel on Climate Change (IPCC) with more complex General Circulation Models (GCMs).

Item Type: Thesis (Other)
Murdoch Affiliation(s): School of Engineering and Energy
Supervisor(s): Ringer, Detlev and Bahri, Parisa
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