The evolution of city-scale GHG emissions inventory methods: A systematic review

Abstract

The capacity of cities to act on climate change mitigation is essential to fulfil the Paris Agreement target. In order to do so, cities should establish an effective climate policy which requires, as a first step, a complete greenhouse gas (GHG) emissions inventory. The accurate city-scale GHG inventory enables cities to develop, implement and track climate solution measures, mainly those related to transportation. The compilation of a city-scale GHG inventory requires a standardized method and up-to-date activity data. This systematic review critically examines 40 articles over the past 20 years to (1) identify city-scale GHG inventory methods being applied worldwide, (2) evaluate how these methods are evolving, (3) elaborate how emissions from transport sector are being estimated, and (4) determine what data types and sources of transport-related data are being used. The review was limited to articles that addressed the process of compilation of a GHG inventory. The results demonstrate that city-scale GHG inventory methods evolved from the Intergovernmental Panel on Climate Change (IPCC) Guidelines to a variety of GHG accounting methods that offer levels of complexity to estimate city-scale emissions. Although GHG inventory methods for city-scale have advanced over the years, almost one third of the articles reviewed were focused on the proposal of a GHG inventory framework, adjusting current methods to each city's reality or proposing new ones. The majority of the cities analysed lack local transport-related data to measure GHG emissions based on the bottom-up approach. Yet, more than 40% of the articles managed to deliver the bottom-up inventory using a diversity of data types and sources. This review shows that there is still a path to achieve a globally compatible method. This would require a joint effort between researchers and city authorities to make international protocols more compliant to each city's data availability along with the improvement of cities data collection.