The ARC3 represents a new "science-into-action" model for integrating climate change into highly complex urban areas that is of great interest to both academic researchers and urban decision-makers as they seek to bridge theory and practice. The first ARC3 provides an in-depth review of research on climate science, mitigation, and adaptation addressed from an urban perspective for key city sectors, including energy and buildings, water supply and wastewater treatment, transportation, and human health as well as for land use and governance. For each of these the urban sector or system is described, specific urban climate risks are identified, adaptation strategies for both climate extremes (including disasters) and mean changes are discussed, as well as potential mitigation actions. Where information is available, the economic aspects of adaptation and mitigation are considered. Policy options are brought forward in each of the topics, and the important role of communities in cities, both as vulnerable populations and as participants in formulating responses to climate change, is also highlighted. Knowledge and applications gaps are identified.
Developing and developed cities
The ARC3 recognizes that there are both similarities and differences between developed and developing city responses to climate change. For example, there is a great deal of fundamental information on climate change projections, vulnerabilities, and risk assessment methods that has a common base in both types of cities. At the same time, there are great differences in the circumstances in developing country cities. These are discussed throughout the topics, with key points brought forward as city case studies. The city case studies, which illustrate challenges, "best practices," and available tools to facilitate actions in developing and developed cities, are presented throughout the text. The case studies cover the status and activities related to climate change on a city-by-city basis.The case studies have been developed by authors drawn from both the research and practitioner communities; such teams are helping to build a cadre of knowledge-providers to aid in implementation of climate change actions in cities around the world.
Multiple stresses and risk management
The topics characterize urban-specific issues integrating social, economic, and physical aspects. There is explicit recognition that cities face multiple stresses – including population pressure, urban poverty, and pollution – and that climate change and these multiple stresses will likely be manifested in intertwined ways.
Another topic covered is the framing of climate change as a risk-management issue. This is evolving into a new paradigm for both mitigation and adaptation (NPCC, 2010). As described in the previous section, disaster risk reduction is an important set of activities challenging many cities, especially in the developing world, and approaches to fostering the intersection of the risk reduction community with the climate change community are put forward.