Abstract
Urban material resource requirements are significant at the global level and these are expected to expand with future urban population growth. However, there are no global scale studies on the future material consumption of urban areas. This paper provides estimates of global urban domestic material consumption (DMC) in 2050 using three approaches based on: current gross statistics; a regression model; and a transition theoretic logistic model. All methods use UN urban population projections and assume a simple ‘business-as-usual’ scenario wherein historical aggregate trends in income and material flow continue into the future. A collation of data for 152 cities provided a year 2000 world average DMC/capita estimate, 12 tons/person/year (±22%), which we combined with UN population projections to produce a first-order estimation of urban DMC at 2050 of ~73 billion tons/year (±22%). Urban DMC/capita was found to be significantly correlated (R2 > 0.9) to urban GDP/capita and area per person through a power law relation used to obtain a second estimate of 106 billion tons (±33%) in 2050. The inelastic exponent of the power law indicates a global tendency for relative decoupling of direct urban material consumption with increasing income. These estimates are global and influenced by the current proportion of developed-world cities in the global population of cities (and in our sample data). A third method employed a logistic model of transitions in urban DMC/capita with regional resolution. This method estimated global urban DMC to rise from approximately 40 billion tons/year in 2010 to ~90 billion tons/year in 2050 (modelled range: 66–111 billion tons/year). DMC/capita across different regions was estimated to converge from a range of 5–27 tons/person/year in the year 2000 to around 8–17 tons/person/year in 2050. The urban population does not increase proportionally during this period and thus the global average DMC/capita increases from ~12 to ~14 tons/person/year, challenging resource decoupling targets.
Highlights
Humankind has become so urbanised that we may refer to the majority of the population and into the foreseeable future, as living in cities
Gross statistical estimation of current urban material consumption We aggregate our sample of 152 cities to produce gross statistics about these major global regions: Africa, Europe, Northern America, EECCA, Latin America, the Caribbean and Western Asia –see table 1
Estimates of urban domestic material consumption (DMC)/capita in table 1 have considerable uncertainty but are bounded within national totals and consistent with development phase and level of urbanisation: Europe, North America and the transition economies of EECCA show the highest DMC/capita; Latin America and the Caribbean is the most urbanised region in the developing world, with 77% of its population living in urban centres and its DMC/capita is significantly greater than Africa and Asia and Pacific
Summary
Humankind has become so urbanised that we may refer to the majority of the population and into the foreseeable future, as living in cities. As cities are the location of much of society’s final consumption, major infrastructure and economic activity, it is valid to ask: ‘what are the material resource requirements of cities in the future?’. National-level, globally consistent accounts of energy [3, 4] and materials flow [5,6,7,8,9] have been developed and standardised to monitor the status and change in resource use. There are far fewer global accounts of urban energy use [10] and none regarding urban materials. Transport, transformation, use and disposal are intrinsically coupled with the energy and greenhouse gas emissions of concern to the international community [11]. Municipal waste material flows continue to be a particular concern at the local government level [12, 13]
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