is, at a particular location where complexity is present and yet when small-scale phenomena can be identified and characterized, where the boundaries of the system are known and where hypotheses about the mesoscale behavior can be tested.
One of the critical tools for geoengineering will be a hierarchy of models that calculate the interactions of the various components under different policy and engineering design choices. These models will aspire to predict the behavior of the complex, interacting system components. Entirely new types of modeling that emphasize the interaction without losing fidelity in representing the components may be required. Models of dynamical systems, chaotic behavior, and emergent phenomena certainly have a role.
The essence of engineering as opposed to science is the focus on design and management. In this light, the focus of an ESE or GES initiative is the eventual production of design approaches and management paradigms that address highly interactive Earth systems where anthropogenic effects play a dominant role and where the overall objective is sustainability. ESE presents a scope and complexity that has never before been addressed by engineers. In some cases, we may be able to extrapolate and modify engineering methods of the past. However, there is no accepted—or even tried—engineering methodology for problems as complex as global change. In fact, Allenby conjectured that ESE will not even be engineering in the usual sense in that it will be less management per se and more purposeful decision making (Personal communication from Brad Allenby to the committee, September 2003). The requirement for social and economic acceptability to this purposeful decision making about Earth will be profound. Many engineering projects have faced and solved what are considered the constraints imposed by the environment and social concerns with varying success. Case studies will show a wide variety of successes and failures in this regard. However, much more