This is largely an urban problem. The vast majority of the planet’s natural resources are consumed by city-dwellers – by their homes, transportation, energy, food, clothes, businesses, industries, and governments. A smaller but still significant portion of our natural capital is eaten up by mines, mills, farms, and other rural industrial activities that produce products used primarily by city-dwellers.

North American cities are by far the worst offenders. If China and India’s rapidly urbanizing population of 2.5 billion consumed natural capital the way we do in Canadian and U.S. cities, we would need the equivalent of four Earths’ worth of natural resources. As we only have one Earth, it’s imperative that we imminently abandon our North American urban model of sprawl, freeways, SUVs, and general overconsumption.

Besides their considerable impact on the environment, 21st-century cities constitute a crucial front in the war against poverty. One billion poor people currently live in urban areas of developing countries, many of whom are forced to inhabit informal and mostly illegal slums. Many more will have to adopt such living conditions if we don’t develop creative, sustainable strategies for building modern cities.

The impact of cities on the world today and over the next century cannot be overstated. Thus, in an effort to build strategies for creating sustainable cities and to conceive of the tools necessary to implement them, I have invited a group of experts to discuss various aspects of the broad subject of cities: ecological footprints, climate change, demographic challenges, social welfare, and more. I hope you will join in the dialogue.