The historian William Cronon among others has noted that, for many environmentalists, the city has traditionally been viewed as the ultimate human environment, and therefore evil: "The boundary between natural and unnatural shades almost imperceptibly into the boundary between nonhuman and human, with wilderness and the city seeming to lie at opposite poles -- the one pristine and un-fallen, the other corrupt and unredeemed." (from Nature's Metropolis) This perception has transitioned into much of the sustainability literature, leading to a widespread impression that cities are clearly "unsustainable," an interesting conclusion given that cities are perhaps the most sustainable artifact that humans have developed.

The failure to understand cities as evolving complex adaptive systems, rather than static processors of materials and energy and producers of waste, is problematic in that it limits the usefulness of the dialog between sustainability advocates and urban systems just at a time when urban systems are about to experience a major leap in complexity. Whether environmental and sustainability considerations can help shape the path along which this accelerating evolution of urban systems will occur is not clear, but certainly the opportunity for such contributions will be substantially limited by a failure to accurately perceive and understand the nature of cities as evolving "systems of systems." Moreover, at least some of the drivers of accelerating change in urban systems can be identified, a necessary step in informing a rational and ethical understanding of the "sustainability" of cities, a task which has yet to be undertaken with any seriousness.

As one example, consider two separate trends that, taken together, will profoundly redefine the nature of urban systems. The first is that cities, like virtually every other complicated human technology, are rapidly incorporating quite sophisticated information systems -- including sensors, information processors and filters, networked computational capabilities, and the like - at a number of different scales. Increasingly, we are designing and building materials, components and subassemblies, buildings, city regions, infrastructures, and other urban subsystems to be “smart,” with significant new information content and capability. Moreover, every major urban system is increasingly also an active node in complex regional and global information, transportation, energy, and financial networks, creating a level of information density and complexity that is entirely unprecedented.

At the same time, the structure and dynamics of information and communication technology (“ICT”) systems are changing fundamentally. Rather than the relatively passive, deterministic, and human-controlled technology that characterized the past, new ICT systems are being designed to be self-defining, self-managing, self-configuring, self-healing, self-optimizing, and self-protecting. This so-called “autonomic” architecture and capability is currently being deployed by ICT firms at all scales, from chips, to computers to computer networks, to communication networks, to the Internet taken as a whole. Such capabilities mark a major leap in device and network functionality. Perhaps more importantly, however, learning capabilities are being built directly into these systems. Thus, for example, an intelligent network will “learn” its own characteristics, and thus be able to identify perturbations beyond normal operating fluctuations, and respond in order to maintain operational functionality (e.g., respond to potential viruses as an immune system would, rather than waiting for human intervention).

Consider now how these two trends intersect and integrate in urban systems. Not only does the city become much more complex in terms of information density and networks, but so do the ICT structures supporting this complexity -- exponentially so. The predictable result is not just an immensely more competent and functional city, but emergent behaviors and characteristics that are both unpredictable and potentially quite powerful -- and ones that occur without passing through human institutions or filters. The potential implications of this change in structure are illustrated by the example of “Black Monday,” Oct. 19, 1987, when, without warning, the US stock market crashed (the Dow Jones dropped 22% in one day). The main reason had nothing to do with economic fundamentals. Rather, it was the poorly understood information structure itself; computer systems that increasingly carried out trades interacted in an unanticipated and unintended way.

As autonomous information system structure becomes ubiquitous at all scales, and as urban systems continue to become increasingly information dense within and among different levels, it will be impossible to determine what the city “knows” or how it will choose to react to changing conditions or threat. Understanding the nature of these “cognitive cities” is a profound challenge, but one that must be met if the discourse on the sustainability of cities is to have any meaningful content at all.

--------
Brad Allenby is professor of civil and environmental engineering at Arizona State University, a fellow at the University of Virginia's Darden Graduate School of Business, and previously was AT&T's vice president of environment, health, and safety.