Our world is facing an unprecedented growth in population, from seven to nine billion people by 2050, of whom 75 percent will live in cities. Mass urbanization, with expanding cities in China, India, the United States, and sub-Saharan Africa, is leading to much greater energy demand, air pollution problems, and climate change.

There is no better backdrop to discuss these challenges than Rotterdam, Europe’s largest harbor city, one of the “dirtiest” cities in the world when it comes to emissions of carbon dioxide and methane, and one of many Dutch cities facing the consequences of global climate change because of its position below sea level. (See related photos: “Nine Surprisingly Gassy Cities.”)

But Rotterdam is also a resilient city, as Mayor