the c emissions increased even less indicating a pervasive historical trend towards decarbonization of the global economy at about per cent per year the share of fossil energy sources taken together increased from to per cent between and now as did the emissions of c as an unavoidable byproduct of combustion consequently energyrelated emissions of c increased fold to about billion tons of carbon gtc in nevertheless their increase has remained at a substantially slower pace than that of energy requirements indicating a strong historical trend towards decarbonization of societies