تعمق در میزان کربن سنگاپور - مقایسه انتشار گازهای گلخانه ای مستقیم و غیر مستقیم از یک سیستم اقتصادی کوچک و باز

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.

There is considerable debate about the contribution of urban areas to global anthropogenic greenhouse gas emissions. Recent estimates calculated that at least 67% of the global energy use and an even larger share of fossil fuel related greenhouse gas (GHG) emissions are emitted from urban activity (International Energy Agency, 2008; Satterthwaite, 2008). Questions therefore arise how to allocate responsibility for those emissions and how to identify effective strategies to abate this significant source of environmental impacts as continuing urbanisation is an overarching trend (United Nations, 2008). The complexities of cities include large numbers of agents, activities and processes. The functionally open character of urban settlements makes the discussion of system boundaries particularly relevant when accounting for their contribution to man made greenhouse gas emissions. Most attempts to allocate responsibility for GHG emissions at a national scale are based on administrative and therefore territorial system definitions. They are mainly focussing on the production side of the economic process. In that view it is aimed to account for emissions at the spatial point where they are released into the atmosphere. A strict focus towards “on-site emissions” nevertheless can leave out emission intensive upstream (or up-wire) processes. Already the production and transport of primary energy carriers required energy inputs, losses and emissions which are not reflected in a strict direct emissions account (Hall and Cleveland, 1981; Cleveland et al., 1984). In the case of secondary energy carriers like electric power, heat networks and petroleum based energy products, which all require conversion processes, those emissions can be considerable and often occur at locations far away from the urban centre where they are consumed. Moreover also the production of general, non fuel commodities abroad which are transported and traded internationally for consumption in other locations require energy and cause greenhouse gas emissions, referred to as indirect and embodied emissions. Especially in more regionalised accounts the contributions of such indirect emissions can be substantial and extend the volume of direct emissions. An alternative rationale towards emissions accounting is therefore to apply a life-cycle perspective in the system definitions. In such a view the system is conceptually not defined spatially but as a socioeconomic unit and emission responsibility is defined by the sum of functional processes or consequential activities in the process chain of production and consumption no matter where they are conducted. Such an approach was also requested in the Johannesburg plan of implementation of the World Summit on Sustainable Development (Commission on Sustainable Development, 2002) and is currently debated in the Marrakech Process of UNEP and UNDESA (UNEP, 2005; Cosbey, 2009; Tamiotti et al., 2009). Responsibility for embodied emissions should not be restricted to account for imported goods. In order to avoid double counting at the global level and arrive at a fair allocation of responsibility to the final consumer, it is important to also consider the indirect emissions embodied in exported goods and subtract them from the net responsibility for indirect emissions (Ahmad and Wyckoff, 2003; Peters and Hertwich, 2008a, Peters and Hertwich, 2008b and Peters and Hertwich, 2008c). This is particularly relevant to urban centres as they are typically also locations of manufacturing, industry and other production processes and provide products to other urban as well as non urban consumers. Finally also accounting for ‘downstream’ emissions arising after use, at the final stage in the life-cycle of a commodity during waste treatment or recycling is relevant when assessing the impacts of cities. If the focus is strictly towards “on-site emissions” such impacts would be effectively externalised when treatment occurs outside of the city limits. The implications of trade with energy and GHG intensive products raised particular concerns, if trading partners have different obligations towards emission reduction targets. Authors identified the potential problems of “carbon leaking” into regulated markets (Peters and Hertwich, 2008a, Peters and Hertwich, 2008b and Peters and Hertwich, 2008c; Hertwich and Peters, 2009) as major obstacle towards international GHG reduction policies and pointed at the unfair market conditions if certain producers (e.g. non participants or non-Annex 1 countries) are able to avoid emission caps, trading schemes or carbon taxes but compete on a single integrated market. This paper uses the example of Singapore, a city-state and open economy to compare results based on different allocation concepts. It is restricted to greenhouse gasses. To our knowledge it is a first attempt to account for indirect greenhouse gas emissions in a time series approach for the city-state of Singapore.

This study used the city-state of Singapore as example to illustrate technical challenges in GHG accounting for economically open urban systems. It compared results for GHG emissions under different accounting conventions: either focussing only on direct emissions from activities on the territory or including indirect emissions from upstream activities or in a third variant also considering exports of indirect emissions, to arrive at a trade corrected net account for indirect emissions. The volume of indirect emissions turned out to be important, with imports of indirect emissions exceeding direct emissions by a factor of 4–5 throughout the time series. Exports of indirect emissions were generally somehow lower but in a similar order of magnitude, between three and four times the direct emissions. These findings indicate that urban scale emission accounts might be of limited value to identify most effective climate change mitigation potentials if they focus solely on direct emissions. The concept of sustainable production and consumption asks to look at emissions over the whole supply chain and report all emissions necessary to maintain urban structure, functions and socioeconomic activity. Otherwise a city could effectively externalise GHG intensive activities upstream and waste treatment activities downstream to appear in a direct flow approach to be GHG effective while functionally still depending on emissions to take place abroad. In another context such strategies have been referred to as environmental cost shifting or ecologically unequal exchange (Muradian and Martinez-Alier, 2001). To identify comprehensive GHG mitigation strategies it is therefore important to also provide information on adjacent activities. An alternative and complimentary view to the spatially defined system definition was presented in this paper. When looking at urban planning and management practice and its translation towards environmental performance indicators, Singapore presents a paradoxical picture: the compact settlement structure, together with well planned and regulated transport systems give rise to expectations of relatively low per capita energy use and emissions. The actual direct emission data on the other side varies widely between different sources and is in general still quite high. In a detailed analysis which reports different industrial sectors, the particular role of export oriented petrochemical industry in Singapore and the significance of bunker fuel is pointed out to explain this performance. This study added a city specific life-cycle view to improve our understanding of the role of urban areas in the global network of trade and resource consumption. More site specific data particularly also of environmental impacts of services and final products would improve such analysis. Also comparative studies on embodied emissions applying different methodologies would be helpful to further develop this field of analysis.