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Summary Report No. 33

Modelling the Global Carbon Cycle for the Past and Future Evolution of the Earth System

S. Franck, K. Kossacki, Ch. Bounama (December 1997)

The Earth may be described as a global system consisting from the components solid Earth, hydrosphere, atmosphere, and biosphere. This system evolves under the external influence of increasing solar luminosity. In spite of this changing external forcing, the Earth's climate has been stabilized by negative feedbacks against global freezing in the past (faint young sun paradox). The future long-term trend of further increasing solar luminosity will cause a further atmospheric CO2 decrease. Atmospheric CO2 will fall below the critical level for photosynthesis and the plant based biosphere will die out.

Based on a model published by Caldeira and Kasting (1992) we investigate the influence of geodynamical phenomena like spreading rates and continental growth on the evolution of CO2 partial pressure and surface temperature of the planet Earth. We find a warmer climate in the past and a shortening of the future life span of the biosphere up to some hundred million years.

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