Cities as nuclei of sustainability?

TL;DR

This paper analyzes urban CO2 emissions and their relation to city size, revealing development-dependent scaling behaviors and suggesting urbanization's differing climate impacts in developed versus developing countries.

Contribution

It introduces a comprehensive analysis of urban GHG emissions scaling with population and proposes density as a key factor influencing emissions.

Findings

Emission scaling varies with development level.

Urbanization benefits in developed countries.

Largest city size influences national emissions.

Abstract

We have assembled CO2 emission figures from collections of urban GHG emission estimates published in peer reviewed journals or reports from research institutes and non-governmental organizations. Analyzing the scaling with population size we find that the exponent is development dependent with a transition from super- to sub-linear scaling. From the climate change mitigation point of view, the results suggest that urbanization is desirable in developed countries and should be avoided in developing ones. Further, we compare this analysis with a second scaling relation, namely the fundamental allometry between city population and area, and propose that density might be the decisive quantity. Last, we derive the theoretical country-wide urban emissions by integration and obtain a dependence on the size of the largest city.