Delving into the carbon footprints of Singapore--comparing direct and indirect greenhouse gas emissions of a small and open economic system

Small and open economic systems like cities face specific challenges for greenhouse gas accounting. They typically import most of their energy requirements as secondary energy products based on conversion processes which caused emissions elsewhere. Emission estimates therefore already require attention not only to direct on-site activities. Moreover, for a comprehensive approach it is suggested to include upstream and downstream processes of connected socioeconomic systems and the indirect life-cycle related emissions of imported and exported goods. Singapore is used in this longitudinal study as an example of an urban scale economy. Accounts for direct emissions are compared with trade corrected estimates of indirect emissions. Results indicate that direct emissions account for only about 20% of the overall upstream emissions necessary to sustain the input side of the economic production process (domestic emissions plus indirect emissions embodied in imported goods). If indirect emissions embodied in exports are considered and subtracted from the previous figure, the trade corrected accounts for direct and indirect emissions still exceed direct emission accounts, although by less than 40%. Given the increasing trends in world trade and urbanisation, indirect pressures of urban systems should be included in discussions of effective and fair adaptation and mitigation strategies.