The 21st century vision that’s emerging is “green cities” — high-efficiency leaders in renewable energy, and recycling, with gardens on the rooftops and solar power lighting up the town.

In this picture, population density is an advantage. Good thing, too. Cities consume 75 percent of the world’s energy. You can’t have a green planet without them in the lead.

This Hour, On Point: Exploring green cities.

Guests:

Joan Fitzgerald, Director of the Law, Policy and Society program at Northeastern University and author of “Emerald Cities: Urban Sustainability and Economic Development”

Jeb Brugmann, urban development consultant, founder of “ICLEI – Local Governments for Sustainability,” an association of over 1,000 local governments and government organizations worldwide that have committed to sustainable development. He’s author of “Welcome to the Urban Revolution: How Cities Are Changing the World.”