This contribution was prompted by the article “Gross Direct and Embodied Carbon Sinks for Urban Inventories” by Mohareb and Kennedy published in this issue. The authors define two types of urban carbon sinks - direct and embodied - and discuss their relation to producer and consumer emissions (and sinks) accounting. This commentary continues that discussion by clarifying boundary considerations and definitions between producer and consumer sinks, and between direct and indirect sinks. Extending the notion of production- versus consumption-based emissions accounting, a corollary for producer and consumer sinks can be drawn. Producer sinks would include direct sequestration through industrial and private activities occurring within a defined territory. Consumer sinks would refer to direct and indirect sequestration activities associated with the consumption of goods and services within the same territory, wherever that sequestration may occur. As with emissions accounting, in carbon sinks accounting I propose that the exact categorization depends on the perspective taken. Clear boundaries and well-defined terminology - historically present in emissions accounting - are critical to this novel approach to sinks accounting.

A determination of the sustainability performance of a company ought to fulfill certain requirements. It has to take into account the direct impacts from on-site processes as well as indirect impacts embodied in the supply chains of a company. This life cycle thinking is the common theme of popular footprint analyses, such as carbon, ecological, or water footprinting. All these indicators can be incorporated into one common and consistent accounting and reporting scheme based on economic inputoutput analysis, extended with data from all three dimensions of sustainability. We introduce such a triple-bottom-line accounting framework and software tool and apply it in a case study of a small company in the United Kingdom. Results include absolute impacts and relative intensities of indicators and are put into perspective by a benchmark comparison with the economic sector to which the company belongs. Production layer decomposition and structural path analysis provide further valuable detail, identifying the amount and location of triple-bottom-line impacts in individual upstream supply chains. The concept of shared responsibility has been applied to avoid double-counting and noncomparability of results. Although in this work we employ a single-region model for the sake of illustration, we discuss how to extend our ideas to international supply chains. We discuss the limitations of the approach and the implications for corporate sustainability.

Cities are thought to be associated with most of humanity's consumption of natural resources and impacts on the environment. Cities not only constitute major centers of economic activity, knowledge, innovation, and governance -- they are also said to be linked to approximately 70% to 80% of global carbon dioxide emissions. This makes cities primary agents of change in a resource- and carbon-constraint world. In order to set meaningful targets, design successful policies, and implement effective mitigation strategies, it is important that greenhouse gas (GHG) emissions accounting for cities is accurate, comparable, comprehensive, and complete. Despite recent developments in the standardization of city GHG accounting, there is still a lack of consistent guidelines regarding out-of-boundary emissions, thus hampering efforts to identify mitigation priorities and responsibilities. We introduce a new conceptual framework -- based on environmental input-output analysis -- that allows for a consistent and complete reconciliation of direct and indirect GHG emissions from a city. The “city carbon map” shows local, regional, national, and global origins and destinations of flows of embodied emissions. We test the carbon map concept by applying it to the greater metropolitan area of Melbourne, Australia. We discuss the results and limitations of the approach in the light of possible mitigation strategies and policies by different urban stakeholders.