Buildings and other engineered structures that form cities are responsible for a significant portion of the global and local impacts of climate change Consequently, the incorporation of building design strategies and materials such as the use of reflective roof materials, or 'cool' roofs, are being widely investigated. However, although their benefits for individual buildings have been studied, as yet there is little understanding of the potential benefits of urban scale implementation of such systems Here we report the development of a new methodology for assessing the potential capacity and benefits of installing reflective roofs in an urbanized area. The new methodology combines remote sensing image data with a building energy computer simulation to quantify the current rooftop reflectivity and predict the potential benefits of albedo improvement. In addition to the direct electricity savings, cool roof systems reduce peak electrical demand in the month of August when the peak demand is at its highest in the case study area. Environmental benefits associated with lowering greenhouse-gas emissions are also substantial The new methodology allows the calculation of payback periods to assist planners to evaluate the potential economic benefits of the widespread installation of cool roof systems. (C) 2010 Elsevier Ltd. All rights reserved.