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Scientists shed light on how the sustainability of cities can be measured

By on September 18, 2018
  • Researchers at the Chair propose the inclusion of social and economic aspects in Life Cycle Assessment (LCA) of cities.
  • Published in the journal Science of the Total Environment, this study goes beyond the state of the art by connecting the three dimensions of sustainable development.
  • Understanding the performance of city LCAs with sustainability perspective paves the way to the standardisation of Environmental City Declarations.

Cities are widely recognised by multilateral bodies and the scientific community as relevant actors in the generation of impacts and as an opportunity for reducing environmental burdens worldwide. At the same time, Life Cycle Assessment (LCA) has been demonstrated to be a good tool for the diagnosis of potential environmental impacts. However, there have not been any developments in the LCA methodology yet to adapt it to contribute to assess and improve the environmental sustainability of cities and help city-level decision makers to achieve the Sustainable Development Goals (SDGs). A study by researchers at the UNESCO Chair in Life Cycle and Climate Change ESCI-UPF (Spain) and the École des Mines de Saint-Étienne (France), published in the journal Science of the Total Environment, goes beyond the state of the art by providing a sustainability performance indicator, with a life cycle perspective and environmental, social and economic information, aiming at facilitating the comparison and benchmarking of results among cities. The impact of a list of 18 cities have been analysed showing how the use of different normalization factors changes its relative impact and, thus, the position of each city on the list.

A literature review of the available tools for assessing cities’ sustainability was previously performed by researchers at the Chair, highlighting the need for working on the City LCA with a sustainability perspective. “City LCA is essential to tackle the big numbers of environmental impacts, as, for instance, cities account for 80% of global greenhouse gas emissions,” explains Jaume Albertí, first author of the study and leader of the Sustainable Construction and Energy Research Line at the Chair. “Currently, in the case of city sustainability assessments, there is a lack of at least one of the following aspects: holistic point of view, multicriterial assessment, LCA perspective and the possibility to compare results among different cities worldwide,” he adds. “Probably, the complexities of both the assessment method and the system under study have been an obstacle for carrying out city LCAs,” points out the researcher.

Monitoring the performance of cites

In order to define LCA items for a complex system such as a city, researchers have determined the goal, and part of the scope in a city LCA: the city Function, the Functional Unit to allow the comparison among cities, and the Reference Flow to quantify impacts. “The function of a city has been defined as ‘providing a proper environment to human beings, allowing them to live with a certain level of prosperity,’ is consistent with the relating values to city development made by Aristotle (384–322 BC) who declared that a city should provide both security and happiness to its inhabitants,” explains Pere Fullana i Palmer, co-author of the study and director at the Chair.

“LCA is precise in assessing environmental aspects of sustainability but lacks social and economic inputs,” points out Fullana i Palmer. To obtain a feasible city LCA, the authors propose to “introduce the social and economic aspects through the use of the UN-Habitat’s City Prosperity Index (CPI), an internationally accepted index which already has been applied to over 400 cities across the world,” he adds. CPI is a composite index used to measure the overall achievements in a city in six dimensions of prosperity that are related to how cities are governed or how they create and distribute socio-economic benefits or prosperity.

“The CPI combined with the number of inhabitants is the normalization factor which is found to be more suitable to avoid problem shifting among sustainability dimensions, avoiding that improvement in one dimension is not achieved at the expense of another dimension, and to avoid the interference of the number of inhabitants when comparing two different cities, such as Addis Ababa and New York,” explains Albertí. Thus, “in order to boost LCA as a proper tool not only for a specific region or cultural group of cities but for any urban region around the world, we consider the number of people who live in the city and the way how they live,” he adds. “This ensures benchmarking sustainability in cities, fostering continuous improvement by transferring the best solutions to other cities.”

This work also includes the analysis of the impact of 18 cities showing how the use of different normalization factors changes the relative impact of each city on the list. “The sustainability reputation of some cities can be increased or decreased not only depending on their number of inhabitants, but also on how cities perform in social and economic terms. For example, the comparison of Barcelona and Zurich’s Global Warming Potential (GWP) shows that, even though Barcelona has a higher GWP than Zurich, if population and prosperity are considered as normalization factors, the modified GWP of Barcelona is lower than that of Zurich,” explains Albertí. “The sample includes cities from different continents and levels of development and, therefore, it can be useful to see how the suggested method is affecting cities’ position,” he adds.

Researchers highlight that the information in this article is a first step to the performance of city LCAs with sustainability perspective which could, in the long run, result in the standardisation of Environmental City Declarations (ECD). Forthcoming research works should state the remaining items of the scope definition in LCA (System boundary definition, and Allocation procedures) in order to set the basis for performing comparative pilot city LCAs. Considering the global consequences of climate change that largely impact urban life, “the results of this study address the need for helping regional, national and local level governance for boosting sustainable development and for policy-makers to have a deeper knowledge of the city alignment with the Sustainable Development Goals,” concludes Fullana i Palmer.

This article is part of Jaume Albertí’s PhD Thesis, within the tyLCA Project of the Sustainable Construction and Energy Research line at the Chair. For more information about the tyLCA Project at the Chair please contact jaume.alberti@esci.upf.edu.

Reference article

Albertí, J., Brodhag, C., & Fullana-i-Palmer, P. (2019). First steps in life cycle assessments of cities with a sustainability perspective: A proposal for goal, function, functional unit, and reference flow. Science of The Total Environment, 646, 1516-1527.

DOI: 10.1016/j.scitotenv.2018.07.377

Download the article for free until September 21, 2018 via Elsevier

Post available in SPANISH