Urbanization is a Major Source of Environmental Degradation

An important new study has just been published in the academic journal PLoS One summarizing our knowledge of what growing urban populations mean for the environment. The authors--Karen Seto, Michail Fragkias, Burag Guneralp, and Michael Reilly--drew the following major conclusions:

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. 

The New York Times picked up on the story and noted that:

While shifting variables make predictions about future growth difficult, the authors write, a few things are clear: because two-thirds of urban areas with populations exceeding five million are in coastal zones at risk from sea-level rise, “inadequate responses to protecting coastal urban areas would be devastating to the economies and infrastructure of 13 percent of the world’s urban population.”

These are obviously important issues since the UN Population Division projects that virtually all of the world's population growth in the next few decades will be in or show up in cities, especially cities of developing nations. Furthermore, note that this refers only to the land near cities. It does not take into account the extensive ecological footprint of urban residents that extends to literally all corners of the earth.