Cities looking to be models of sustainability must look beyond city limits to the global flow of goods and materials into their realm, Swedish researchers say. Writing in the Royal Swedish Academy of Sciences journal Ambio, scientists say sustainable city initiatives often ignore the environmental footprint from imported goods and services such as food, water and energy. City leaders\' vision of sustainability often stops at the city limits, they say, but should take into account the impacts on non-urban regions that often provide resources to urban areas. \"Urban areas drive much of the global changes we see, whether in energy use, food supply, resource depletion or land-use change,\" says study lead author Sybil Seitzinger of the International Geosphere-Biosphere Program based in Stockholm. Sustainable cities will require adequate information on resource flows and their impacts, she said, preferably in near-real-time and on a global scale so they can be aware of how resources consumed within a city are sourced, produced and transported. A partnership between \"sustainable\" cities and between cities and non-urban regions could provide the foundations for a more sustainable approach to urbanization and urban living this century, the researchers wrote. \"The sustainability of a city can no longer be thought of in isolation from the combined resource use and impacts of cities globally.\"