By 2050, the human population is projected to reach a population size between 7.6 and 10.6 billion (United Nations, 2005). This dramatic increase in the human population will place a tremendous burden on the Earth's social and ecological systems. In 2007, more than half of the human population is expected to live in urban areas, the first time in history that more humans have lived in cities versus rural settlements (United Nations, 2004). In response to this increasing pressure, many have called for real-world approaches to achieving sustainability, particularly in urban landscapes. Monto et al. contend that the lack of consensus over the definition, operational goals, and objectives of sustainable development will make implementation of sustainability difficult. The objectives of their new book are to (a) consolidate and present concepts, principles, and perspectives regarding sustainability; (b) guide development of models for large systems such as cities and other human settlements; (c) demonstrate the use of models for policy development; and (d) encourage more research into sustainable development and decision support tools for sustainability. The authors address a critical question in this timely book: How do we assess and forecast the sustainability of human settlements?
Monto et al. provide a useful overview of the pertinent issues surrounding sustainability and human settlements in the first two chapters. There has been much debate on the definition and concept of sustainable development (Lele, 1991). The authors effectively characterize the difficulties that arise from the various perceptions of sustainable development. In addition, they detail the evolution of the concept from the publication of Our Common Future (World Commission on Environment and Development, 1987) to recent times and the shifting focus between economic and environmental sustainability. The clearest communication of those concepts necessary to any discussion of sustainability comes at the end of the first chapter. Here, the authors state the goals of the three pillars of sustainability (i.e., environment, economy, and society) and attempt to extract commonality from the myriad definitions of sustainable development currently in use. They assert a common goal should ally all definitions of sustainability: to maintain and support human development. In other words, Monto et al. suggest sustainability must focus on humans and their quality of life. Those in environmental sciences may disagree (as I did initially), contending that sustainability focuses on human development and the ecosystems on which humans rely. However, the authors take extra strides to explain that they are using the term development to encompass all aspects of human settlements, from culture and economics to components of the built and natural environment. It is unclear whether this broadening of the term will ultimately be useful. However, by compiling the many definitions, indicators, and principles of sustainable development, the authors provide a valuable resource for anyone making their first foray into these troubled waters. This is particularly true given that "sustainability science" is currently splintered into many "traditional" fields of inquiry. The National Academy of Sciences (USA) recently reported that articles dealing with sustainability sciences have increased 15% to 20% in the last decade, yet no single journal has arisen as a forum to unite the field (Clark, 2007). Thus, this discussion will be useful to many workers not formally schooled in the fundamentals of sustainable development and to those who are only familiar with the reigning definition of sustainability within their own specialty.
At the core of this book is the development of an integrated model for sustainable human settlements. Chapters 3 through 5 address the authors' goals of developing models for human settlements and demonstrating the use of such models for policy development. Monto et al. argue for an integrated approach to modeling; only by incorporating the environment, economics, and social factors will practical solutions arise. The general purpose of the model developed by the authors is to assess the sustainability of human settlements and to make forecasts of the future. The authors discuss model development and model simulation in separate sections of the book. This distinction is a strength of the book and an important concept for those developing models. The authors stress the need to decide what the model should be able to accomplish before launching into the actual simulation techniques (identifying variables, developing mathematical models, creating software, etc.). In discussing the model concept, the authors are careful to explain each component they believe is necessary for an integrated model. Foremost in this list is the concept of systems thinking and, relatedly, acknowledgement of the interrelatedness of human and natural systems. Few would argue against sustainability models taking a holistic approach. The challenge comes in implementation.
Heuristically, Monto et al.'s approach is based on the belief that sustainability of a settlement is determined by community attitude and living environment. The model concept can be summarized by the following equation (p. 110):
{(Existing State) + (Attitude)} = Future State
The existing state is delineated by the present status of the built and natural environment, whereas attitude represents the prevailing community mindset. Because attitude is one of the determining factors of sustainability, the authors propose using methods to incorporate qualitative or subjective variables into the model rather than relying purely on quantitative variables. However, the authors do not thoroughly address issues surrounding how to measure attitude. When dealing with environmental impacts, the authors focus on the concept of the "living environment," which comprises the built environment plus the natural environment in the area surrounding human settlements. Again, although this concept is likened to an ecological footprint, the authors do not provide any practical solutions to defining the living environment. Overall, their focus is on the role community attitudes play in shaping actions.
After the authors define the model concept, they discuss the simulation model or how to implement the concept. The proposed simulation model uses cross-impact analysis, specifically Kane's Simulation (KSIM) and Geographic Information Systems (GIS). KSIM is used to accommodate both qualitative and quantitative variables when making projections of future conditions. In a cross-impact analysis described by the authors, all important variables are identified and organized into a matrix that emphasizes the interactions between each pair of variables, expressed as a coefficient between -1 and 1. The interaction coefficients are determined either by empirical estimation (e.g., data collection or other formal methods) or by more informal approaches (e.g., using expert opinion). The analysis then involves calculating the net result of all impacts of other variables on a single variable of interest. The authors provide a brief example of how they propose using KSIM; however, for those not already familiar with KSIM or similar models, the discussion is cursory. No other techniques for incorporating qualitative data are mentioned, which leaves the reader wondering what other viable options for use in sustainability models are available and how they would compare to KSIM.
Once the KSIM model is developed, the authors discuss performing a crossimpact analysis with GIS. The authors highlight similarities between KSIM and GIS and how the two can be used together to make projections about the trajectory of a settlement in reaching sustainability. This approach is also described in Mani, Varghese, and Ganesh (2005). The authors give a brief example of how the model can be used to simulate water quality trends around a lake, but the book would be improved by a more detailed example of how to actually apply the model in the real world. The authors also fail to suggest a preferred procedure for developing and/or verifying the interaction coefficients or how to reconcile multiple coefficient estimates that arise from different approaches. How do you weigh expert opinion versus assessing stakeholder involvement? An additional drawback of the proposed simulation model is that it only projects increasing or decreasing trends over time. Such results are helpful for raising awareness and working within targeted sectors of a population. However, many decision makers and managers will almost certainly come away with the desire for the more detailed information necessary to implement practical solutions. Working from the authors' own example of water quality, it would be critical to know not only if a water quality variable is degrading, but also if the variable reaches a level that threatens environmental and/or human health and thus triggers management or policy action to promote sustainability. Monto et al. do recognize this limitation of the simulation model and propose incorporating methods to forecast the amount of change as an area for further research.
One area in which the proposed model may be useful is in identifying variables and locations, which will require more investigation. Interaction matrices and GIS have been used successfully in this way, specifically to identify areas in Surrey, England, that are susceptible to poor air quality and warrant further study (Mavroulidou, Hughes, & Hellawell, 2004).
Overall, this new book provides a convincing argument for developing integrated models that include qualitative models and identifies possible approaches and areas for future research. The authors provide one option for an integrated model rather than the integrated model of sustainability. The book suffers from a lack of detailed examples on how to