The conversion of Earth's land surface to urban uses is one of the most irreversible human impacts on the global biosphere. It drives the loss of farmland, affects local climate, fragments habitats, and threatens biodiversity. Here we present a meta-analysis of 326 studies that have used remotely sensed images to map urban land conversion. We report a worldwide observed increase in urban land area of 58,000 km2 from 1970 to 2000. India, China, and Africa have experienced the highest rates of urban land expansion, and the largest change in total urban extent has occurred in North America. Across all regions and for all three decades, urban land expansion rates are higher than or equal to urban population growth rates, suggesting that urban growth is becoming more expansive than compact. Annual growth in GDP per capita drives approximately half of the observed urban land expansion in China but only moderately affects urban expansion in India and Africa, where urban land expansion is driven more by urban population growth. In high income countries, rates of urban land expansion are slower and increasingly related to GDP growth. However, in North America, population growth contributes more to urban expansion than it does in Europe. Much of the observed variation in urban expansion was not captured by either population, GDP, or other variables in the model. This suggests that contemporary urban expansion is related to a variety of factors difficult to observe comprehensively at the global level, including international capital flows, the informal economy, land use policy, and generalized transport costs. Using the results from the global model, we develop forecasts for new urban land cover using SRES Scenarios. Our results show that by 2030, global urban land cover will increase between 430,000 km2 and 12,568,000 km2, with an estimate of 1,527,000 km2 more likely.

This paper introduces urban land teleconnections as a conceptual framework that explicitly links land changes to underlying urbanization dynamics. We illustrate how three key themes that are currently addressed separately in the urban sustainability and land change literatures can lead to incorrect conclusions and misleading results when they are not examined jointly: the traditional system of land classification that is based on discrete categories and reinforces the false idea of a rural-urban dichotomy; the spatial quantification of land change that is based on place-based relationships, ignoring the connections between distant places, especially between urban functions and rural land uses; and the implicit assumptions about path dependency and sequential land changes that underlie current conceptualizations of land transitions. We then examine several environmental "grand challenges" and discuss how urban land teleconnections could help research communities frame scientific inquiries. Finally, we point to existing analytical approaches that can be used to advance development and application of the concept.coupled human-natural systems | land change science U rbanization and land change are two global processes with far-reaching consequences. Although the two are tightly intertwined, their literatures and analytical frameworks were largely developed separately. We argue that these parallel but distinct conceptualizations limit progress in these fields and in sustainability science, specifically given the environmental impacts of urbanization on the land system, and associated social and political challenges. The magnitude and accelerating rate of contemporary urbanization are reshaping land use locally and globally in ways that require a reexamination of land change and urban sustainability. Worldwide, urban populations are projected to increase by almost 3 billion by 2050 (1) and the total global urban land area by more than 1.5 million square kilometers-an area three times the size of Spain-by 2030 (2). Urban economies currently generate more than 90% of global gross value added, meaning few rural systems are unaffected by urbanization (3). Given such trends, we must reconsider how we conceptualize the many connections and feedbacks between urbanization and land change processes. To date, a large body of literature has considered the proximate land changes brought about by urbanization, but the more distant land-use implications of urbanization remain underexamined.In climate science, the concept of teleconnections refers to climate anomalies that correlate over large geographic distances. During warm phases of the Atlantic multidecadal oscillation, for instance, the incidence of synchronous wildfires increases in the western United States (4). The virtual shrinking of distances between places, strengthening connectivity between distant locations, and growing separation between places of consumption and production are emerging topics in "telecoupled" human-natural systems (5-7) and tropical teleconnections ...

Contemporary urbanization differs from historical patterns of urban growth in terms of scale, rate, location, form, and function. This review discusses the characteristics of contemporary urbanization and the roles of urban planning, governance, agglomeration, and globalization forces in driving and shaping the relationship between urbanization and the environment. We highlight recent research on urbanization and global change in the context of sustainability as well as opportunities for bundling urban development efforts, climate mitigation, and adaptation strategies to create synergies to transition to sustainability. We conclude with an analysis of global greenhouse gas emissions under different scenarios of future urbanization growth and discuss their implications.

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