Recent Past and Future of the Global Carbon Cycle
Fred T. Mackenzie, A. Lerman, L. M. B. Ver, 2001. "Recent Past and Future of the Global Carbon Cycle", Geological Perspectives of Global Climate Change, Lee C. Gerhard, William E. Harrison, Bernold M. Hanson
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The global carbon cycle has been affected by four major perturbations owing to human activities on land, and global temperature change since the year 1700. The cycle has been, and continues to be, forced by global emissions from fossil-fuel burning, land-use change, agricultural fertilization of croplands, organic sewage discharges, and a slight temperature rise. The atmospheric carbon- dioxide (CO2) change in the past 300 years, as computed from our model analysis, agrees well with the observed increase. The anthropogenic perturbations on land have resulted in an increased delivery of carbon to the coastal ocean and changes in its trophic status towards increased net heterotrophy (remineralization of organic carbon exceeding its in situ production). Future increases in emissions of carbon from land, based on the projections of the Intergovernmental Panel on Climate Change (IPCC) and the Kyoto Protocol to the United Nations Framework Convention on Climate Change (UNFCCC), suggest increases in atmospheric CO2 to 495 and 435 parts per million by volume (ppmv), respectively, by the mid-twenty-first century The net release or uptake of carbon on land involving phytomass and soil organic carbon depends strongly on patterns of land use. In particular, significant, continuous deforestation of tropical and Russian forests, along with continuous increase in global mean temperature, could lead to a weakening of the hypothesized terrestrial sink for the 1990s during the twenty-first century. Furthermore, an increase in atmospheric CO2 leads to a lower supersaturation state of coastal ocean water with respect to calcite and aragonite, which may result in lower rates of carbonate storage in shallow oceanic areas. Weakening of the oceanic thermohaline circulation (“the conveyor belt”) may result in a greater transport of atmospheric CO2 to coastal ocean waters, at the expense of its reduced transport to the surface open ocean.