Ecological planning of cities is now assumed by many regulators to be a win-win proposition and numerous initiatives on the "greening of cities" are taking shape across the world. No longer are Curitiba in Brazil or Chatanooga in Tennessee the outlier case studies that frequented so many conference presentations. Cities are greening through multiple pathways and Matthew Kahn's new book Green Cities, attempts to understand this trajectory through the lens of economic analysis. The book's theoretical core revolves around the concept of the Environmental Kuznets Curve (EKC) - an economic hypothesis that gained much currency in the nineteen nineties by suggesting that economic prosperity initially leads to environmental decline but that eventually a self-correction mechanism then leads to environmental controls. Kahn notes that he was led to write this book after reading the Danish statistician Bjorn Lomborg's bestseller The Skeptical Environmentalist in which data that indirectly supported the EKC hypothesis was presented.



The author is, however, quite nuanced in his analysis and does not blithely support the Cornucopian view that self-correction will take place in all circumstances. He first delineates the key attributes of environmental quality in urban areas, based on a review of environmental economics literature. In particular, air quality, gasoline consumption and use of public transit are given prominence. The data suggests a compelling case for the EKC hypothesis for air and noise pollution. Cities that have passed a certain threshold of income tend to have more clean and less noisy surroundings per capita.



Kahn also acknowledges that the EKC analysis has its limitations since the spatial quality of growth of cities and migration demographics are not adequately captured in this analysis. While acknowledging this limitation, Kahn also misses some of the most salient attributes of "Green Planning," in terms of parks and pedestrian space or ecosystem-based water and drainage infrastructure that have been known to planners, at least since Ian McHarg's Design with Nature (1967).



As an economist, Kahn is perhaps too preoccupied with the aggregate trends and less concerned with understanding what has worked in the greening process itself in terms of community acceptance. This is where, Kahn would have been better served by venturing beyond urban economics and also exploring the vast literature on environmental planning and consumer psychology. Indeed, the true mark of sustainability in cities is that the well-intentioned efforts at pollution reduction and green design can in fact be sustained through changes in political office.



Some of the chapters in the book hint at this integrative analysis by providing some data on consumer preferences and voting behavior such as the analysis of Proposition 185 ( a tax increase on gasoline) as a function residential distance form the business center. However, the confluence of political factors, social pathologies, and planning constraints that can lead to such behavior are not adequately considered. The literature on Green Urbanist movements would also have been important to consider in this regard (Beatley, 2000).



There is also a significant temporal disconnect between greening efforts that follow the path of economic development and the planning process itself. Plans for greening are often developed several years in advance of implementation and whether or not economic development is synchronous with that planning horizon is not clearly presented in the book.

Referring to the planning literature, Kahn would find that even some of the indicators for sustainability have been studied in great detail by planners as well and might be quite useful for his own quantitative analyses (Berke and Conroy, 2000). Furthermore, the quiet success stories in the developing world can often get missed in macro analysis of this kind. For example, what would explain the relatively green policies in Bogota, Colombia that also defy the conventional EKC trajectory.



Despite these shortcomings, Kahn has provided an important contribution to the analytical discourse on the greening of cities. He has successfully managed to present relatively esoteric economic methods for an informed policy audience within the span of a short paperback book, which is itself an achievement.