Carbon metrics for cities: Production and consumption implications for policies

The estimated cities' contribution to climate change varies depending on the methods chosen by a given city for compiling its greenhouse gas (GHG) emission inventory. This study provides an interpretative synthesis of existing research to explore the differences of three emerging approaches to city-level GHG emissions accounting, based on methodological dimensions: boundary-setting, the categorisation of emissions and the type of emissions. The policy relevance and implications of selecting different system boundaries are explored: each approach can reveal important information which the others fail to identify. This suggests the value of using different and complementary approaches to address as many policy questions and relevant actors possible in climate action planning. Next, key methodological considerations that arise in target-setting approaches involving bringing the emissions balance to zero are presented. An analysis of actual 'net-zero emission' concepts used by eight cities reveals that their precise meaning and applicability remain ambiguous. Finally, to improve both the transparency about such metrics and their usability for policy and decision-making, this paper synthesises all key considerations occurring from the analysis of inventorying approaches and net-zero targets into a reporting and communication framework. Policy relevance Many cities are assuming responsibility for measures to mitigate climate change, but they need greater clarity on 'climate neutral' or 'net-zero' approaches. Each city’s intended purpose needs careful alignment with a choice of methods. The diverse accounting and target-setting landscape and the associated policy implications are elucidated. This can empower more cities to select appropriate methods and set ambitious targets. Calculation of a GHG emission balance is a means to an end and not the end itself. Its purpose is to show the options for action and measure success. Non-transparent methods involve reputational and ethical risks for city governments. A framework to improve transparency is presented. Dual-accounting approaches involving both production and consumption are now the new trend. Individual actors must be able to identify their influence and potential action scope for mitigating climate change. Agreement is needed on how to approach consumption-based accounting and create more city-specific data.