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The original goal of the research presented here was to quantify by world region, the contribution of urbanized areas to global greenhouse gas (GHG) emissions (EDGAR, 2011). Regressions on population density and growth rate, GDP, and heating/cooling degree days, as well as a row of other non-significant variables, show that the contribution of urban extents is between 38% and 49% of total emissions (Marcotullio et al., 2012). In spite of using very liberal definitions of urban extents (GRUMP, 2011) this is at the low end of academic estimates (Satterthwaite, 2008; WEO, 2008; Dhakal, 2010). It is no surprise that the relative weight of individual variables varies by world region and economic development. We were, however, very surprised to find that around the world, the highest levels of GHG emissions are in a belt 20-40 km around urban centres. This result is consistent using both traditional fixed-effects and spatial regression techniques, which will be discussed in detail in this paper. There are variations (e.g. the role of African suburbs is smaller than that of their Asian and European counterparts) but the signature prevails. We suggest that this has consequences for both planning and geography theory as well as for policy. In spite of globalization, we have very few local indicators that are so consistently the same across cultures, economic and physical regimes. On a practical level, our results are an urgent reminder that cities by and large are rather efficient constructs while the biggest impacts on minimizing GHG emissions can be achieved by optimizing suburban energy use and transport.



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