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- ItemThe millennial atmospheric lifetime of anthropogenic CO2(Dordrecht [u.a.] : Springer, 2008) Archer, D.; Brovkin, V.The notion is pervasive in the climate science community and in the public at large that the climate impacts of fossil fuel CO2 release will only persist for a few centuries. This conclusion has no basis in theory or models of the atmosphere/ocean carbon cycle, which we review here. The largest fraction of the CO2 recovery will take place on time scales of centuries, as CO2 invades the ocean, but a significant fraction of the fossil fuel CO2, ranging in published models in the literature from 20-60%, remains airborne for a thousand years or longer. Ultimate recovery takes place on time scales of hundreds of thousands of years, a geologic longevity typically associated in public perceptions with nuclear waste. The glacial/interglacial climate cycles demonstrate that ice sheets and sea level respond dramatically to millennial-timescale changes in climate forcing. There are also potential positive feedbacks in the carbon cycle, including methane hydrates in the ocean, and peat frozen in permafrost, that are most sensitive to the long tail of the fossil fuel CO2 in the atmosphere. © 2008 The Author(s).
- ItemGeoengineering climate by stratospheric sulfur injections: Earth system vulnerability to technological failure(Dordrecht [u.a.] : Springer, 2009) Brovkin, V.; Petoukhov, V.; Claussen, M.; Bauer, E.; Archer, D.; Jaeger, C.We use a coupled climate-carbon cycle model of intermediate complexity to investigate scenarios of stratospheric sulfur injections as a measure to compensate for CO2-induced global warming. The baseline scenario includes the burning of 5,000 GtC of fossil fuels. A full compensation of CO2-induced warming requires a load of about 13 MtS in the stratosphere at the peak of atmospheric CO2 concentration. Keeping global warming below 2°C reduces this load to 9 MtS. Compensation of CO 2 forcing by stratospheric aerosols leads to a global reduction in precipitation, warmer winters in the high northern latitudes and cooler summers over northern hemisphere landmasses. The average surface ocean pH decreases by 0.7, reducing the calcifying ability of marine organisms. Because of the millennial persistence of the fossil fuel CO2 in the atmosphere, high levels of stratospheric aerosol loading would have to continue for thousands of years until CO2 was removed from the atmosphere. A termination of stratospheric aerosol loading results in abrupt global warming of up to 5°C within several decades, a vulnerability of the Earth system to technological failure. © 2008 The Author(s).
- ItemReduction of biosphere life span as a consequence of geodynamics(Abingdon : Taylor and Francis Ltd., 2000) Franck, S.; Block, A.; Von Bloh, W.; Bounama, C.; Schellnhuber, H.J.; Svirezhev, Y.The long-term co-evolution of the geosphere-biosphere complex from the Proterozoic up to 1.5 billion years into the planet's future is investigated using a conceptual earth system model including the basic geodynamic processes. The model focusses on the global carbon cycles as mediated by life and driven by increasing solar luminosity and plate tectonics. The main CO2 sink, the weathering of silicates, is calculated as a function of biologic activity, global run-off and continental growth. The main CO2 source, tectonic processes dominated by sea-floor spreading, is determined using a novel semi-empirical scheme. Thus, a geodynamic extension of previous geostatic approaches can be achieved. As a major result of extensive numerical investigations, the 'terrestrial life corridor', i.e., the biogeophysical domain supporting a photosynthesis-based ecosphere in the planetary past and in the future, can be identified. Our findings imply, in particular, that the remaining life-span of the biosphere is considerably shorter (by a few hundred million years) than the value computed with geostatic models by other groups. The 'habitable-zone concept' is also revisited, revealing the band of orbital distances from the sun warranting earth-like conditions. It turns out that this habitable zone collapses completely in some 1.4 billion years from now as a consequence of geodynamics.
- ItemLong-term evolution of the global carbon cycle: Historic minimum of global surface temperature at present(Abingdon : Taylor and Francis Ltd., 2002) Franck, S.; Kossacki, K.J.; Von Bloh, W.; Bounama, C.We present a minimal model for the global carbon cycle of the Earth containing the reservoirs mantle, ocean floor, continental crust, continental biosphere, and the kerogen, as well as the aggregated reservoir ocean and atmosphere. This model is coupled to a parameterised mantle convection model for describing the thermal and degassing history of the Earth. In this study the evolution of the mean global surface temperature, the biomass, and reservoir sizes over the whole history and future of the Earth under a maturing Sun is investigated. We obtain reasonable values for the present distribution of carbon in the surface reservoirs of the Earth and find that the parameterisation of the hydrothermal flux and the evolution of the ocean pH in the past has a strong influence on the atmospheric carbon reservoir and surface temperature. The different parameterisations give a rather hot as well as a freezing climate on the early Earth (Hadean and early Archaean). Nevertheless, we find a pronounced global minimum of mean surface temperature at the present state at 4.6 Gyr. In the long-term future the external forcing by increasing insolation dominates and the biosphere extincts in about 1.2 Ga. Our study has the implication that the Earth system is just before the point of evolution where this external forcing takes over the main influence from geodynamic effects acting in the past.