Reducing energy and material flows in cities

In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: In the decades to come, the majority of humans will live in urban settings. Consequently, the role of cities in reducing socioeconomic material and energy flows is increasingly recognized. We examine the recent literature on urban energy and material use, and their reduction potential, focusing on three aspects: the urban form, the urban building stock, and urban consumption patterns. Although there is clear evidence of the huge saving potential resulting from better urban form and better building design, implementation remains an open issue. Regarding urban consumption patterns, we point out that there is increasing evidence that household income strongly correlates with embodied energy and material use. This has implications regarding how urban specific energy and material flows should be measured, but might also lead to the insight that technical fixes will eventually be offset by the income effect. Although not the focus of this review, social inequalities in using or having access to resources in cities are stressed as a largely neglected dimension of the debate. Introduction Globally, in the past hundred years, human population increased fourfold while material and energy use increased tenfold. At present humanity uses 500 Exa-Joules of primary energy and extracts 60 billion tones of raw materials annually [1,2]. However, huge inequalities in per capita material and energy use pertain between countries and world regions. The highest consuming 10% of the world population uses 40% and 27% of the world's energy and materials respectively, and the richest 10% accounts for 39% of the world's GDP [3]. This scale as well as the ongoing dynamic of the socioeconomic material and energy throughput ('social or industrial metabolism' [4,5]) poses huge challenges for society, including exhausting the best fossil fuel and ore deposits, overuse of productive lands, extreme pressure on biodiversity, and massive emissions of climate changing gases with potentially disastrous consequences [6]. Much of the research related to reducing material and energy flows has been focusing on either the national level, targeting at a decoupling of economic growth from resource use or on the equipment (product) level, targeting at the potential for efficiency improvements. Since the mid-1990s, however, the potential role of cities in reducing societal material and …