Flöter, Janine (2009) A simple model for the global surface warming pattern. (Diploma thesis), Christian-Albrechts-Universität, Kiel, Germany, 72 pp.

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Abstract

According to the IPCC AR4 the geographical patterns of projected surface air temperature warming show greatest temperature increases over land (roughly twice the global average temperature increase) and at high northen latitudes, and less warming over the southern oceans and North Atlantic, consistent with observations during the latter part of the 20th century. The developed simple climate model that only considers simplified representations of central feedback emchanisms in the climate system is indeed able to reproduce the major features of this global surface warming pattern. The global average temperature change lies well within the range suggested by current IPCC models, suggesting that the basic physics explain most of that pattern. Local deviations betwen the simple model result and that of the multi-model mean response of IPCC models lie within the range of single GCMs, since most complex models differ from the ensemble mean as well. Several experiments were undertaken in order to show the effects of single feedback mechanisms in combination with each other. The known effects of positive feedbacks, such as water vapor and ice-albedo feedback, and negative feedbacks, such as the latent heat feedback, are acting amplifying and dampening, respectively. The most important feedback mechanism is the water vapor feedback which is roughly doubling the model's sensitivity to external forcing. The ice-albedo feedback is amplifying the temperature change in those regions that experience seasonally varying ice or snow cover. However, several physical processes had to be parameterized in order to keep the model as simple as possible. This, however, leads to model failures in reproducing all details of the complex climate system in response to climate change conditions. Nevertheless, it was not the aim of this work to develop one more climate model that is reproducing just a global warming response but to come up with a simplified model version that allows experimental tests of physical relations. This goal indeed has been achieved. In conclusion, the developed simple climate model is only appropriate for clearing the most general features of climate change under a global warming scenario with increasing CO2 concentration. But it may be used to study the effect of single feedback processes under very simplified conditions. The low computation time and simple structure of this conceptual model suggest a usage as a 'educational tool'. Further improvement and expansion will certainly lead to more realistic results, which than surely agree to a certain limit with the results of more complex models.

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