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| The Earth is a complex system, and its overall condition (state) at any time is determined by Geosphere-Biosphere interactions. The state of the system as a whole changes over time, e.g., ice ages to interglacials. We, therefore, consider system state as a descriptor of, for example, climate. The timescales of the processes driving the interactions between the Geosphere and Biospheres vary. However, many of them are long, i.e., occurring over hundreds of thousands to millions of years. During periods of relative stability in the Earth system state, Geosphere-Biosphere interactions are in a kind of balance or “quasi-equilibrium.” Changes in system state tend to occur when this quasi equilibrium is disturbed through a change in timescales of one or more of these interactions. Examples here would include bolide impacts (an order of magnitude time-scale change in energy flow occurring within the Geosphere) and the evolution of photosynthesis (an order of magnitude change in element flow mediated by the Biosphere). The anthropogenic release of carbon to the atmosphere is occurring at a rate that is ~200 times faster than the rate of the geological transport of carbon back to the Earth’s mantle. This rapid change in element (carbon) flow thus represents a disruption in the balance between the interactions of the Earth system components that has characterized the Holocene and potentially can lead to a transition in the Earth system state. The turnover of C in the Biosphere is, however, also a rapid process. This means that the potential for stimulating biological carbon flow toward lowering the CO2 concentration in the atmosphere is realistic on timescales relevant for humanity. | |
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