The limited availability of low entropy energy is the ultimate constraint on urban systems and their long-term well-being. Local air pollution and global climate change is the most topical 'high-entropy expression' of burning fossil fuels to power the highly organised urban lifestyles. The energy use by building type was analysed for millions of existing and new buildings, accounting for differences such as climate and building design was studied by the World Business Council for Sustainable Development (WBCSD). The Internet underpins global communications as never before networks of internet users generate virtual cities. The resource use of modern cities requires a fundamental revision, which in turn, requires new approaches to economic theory. The work of ecological economists Herman Daly and Robert Costanza is an important intellectual resource in this context. Electronic wastes are the ultimate example of twenty-first century entropy, and here the problem of downcycling is particularly pronounced.