The life span of the biosphere revisited

How much longer the biosphere can survive on earth is reexamined using a more elaborate model than that of Lovelock and Whitfield (1982). The model includes a more accurate treatment of the greenhouse effect of CO2, a biologically mediated weathering parametrization, and the realization that C4 photosynthesis can persist to much lower concentrations of atmospheric CO2. It is found that a C4-plant-based biosphere could survive for at least another 0.9 Gyr to 1.5 Gyr after the present time, depending respectively on whether CO2 or temperature is the limiting factor. Within an additional 1 Gyr, earth may lose water to space, thereby following the path of Venus.