by Carl Pierer
In a time of rapid urbanisation, cities distil contemporary issues. By 2050, more than two thirds of the world's population will live in an urban environment (DESA, 2012). Social questions, political problems, and environmental concerns are increasingly raised in an urban context. In particular, due to the concentration of people and consequently economic activity, cities are large contributors to the global greenhouse gas (GHG) emissions and responsible for 40% of GHG emissions from transport (I.E. Agency, 2008). This suggests that a greener organisation of cities can make a substantial contribution to mitigating climate change. The argument here is twofold. First, we present the argument for mitigating by changing the urban form, in particular to a dense and circular city. Secondly, we present the case of Curitiba, illustrating that urban form can significantly reduce GHG emissions from transport, even if the city does not conform to the ideal of high density and circularity.
The theoretical framework for modelling the city is relatively simply. The standard, classical economic model of the (monocentric) city supposes that there is a central business district (CBD) in which all economic activity occurs. City-dwellers commute to the CBD in the morning and back to their residences in the evening. Since this is an economic model, people try to maximise their utility given their income. The utility depends only on the size of living space and the length of the commute. Because a longer commute incurs higher costs to the commuter, the closer a place is to the CBD, the higher the demand from people wanting to live there. This in turn means higher rent prices, and so less living space for the same amount. The model is simplified by allowing a linear trajectory from each point of the city to the CBD. Consequently, the city according to this model is radially symmetric. If we look at the density of the city according to distance from the CBD, we see an exponential decay. That is, near the CBD the city is densely populated (meaning, in particular, high rising buildings), but further away the density is falling (bigger houses, fewer people, the classical suburb scenario).
Of course, this model is rather simplistic and many cities are not in line with the predictions. Some points along which this model has been developed include to allow for multiple centres of economic activity or for other desirable amenities such as distance to green spaces. However limited the model may be, it does illustrate nicely that the urban form is a major factor influencing certain sustainability issues (something that has been confirmed by empirical studies).