Reducing the Carbon and Sulfur Load of the Atmosphere. Assessing Global Decarbonization and Desulfurization and the Future of a Low-Carbon World

For more than a century human activities have been affecting two key biogeochemical cycles, carbon and sulfur. Substantial declines in average carbon intensity (carbon per gigajoule), especially in Western countries, have not been translated into an absolute decline of global emissions, largely due to large emissions increases in Latin America, Africa and, above all, in Asia. In contrast, global desulfurization has taken place not only in relative but also in absolute terms: we have seen not only lower sulfur intensities per unit of liberated energy but substantial decline in total sulfur emissions. We have accomplished this despite a massive increase in global combustion of coal thanks largely to an effective technical fix (flue gas desulfurization). There are no imminent prospects for any major reductions in absolute emissions of carbon dioxide. In view of climate change, this seems critical because the atmospheric behavior and the future levels of absorbed outgoing radiation are indeed determined by the absolute atmospheric levels of the gas, not by reductions of relative burdens per unit of product or service. The next two decades will prove to be crucial.