The first Earth Day was held 40 years ago. Back then, the big environmental fears had to with overpopulation and a vision of the future that involved city dwellers needing gas masks. You've got to admit, when today's top issues involve a green economy and geo-engineering, times sure have changed. Friday at 9, Regina Brett and guests take a look back at the last forty years of greening the planet. What can we learn today from the successes and mistakes of the past?

Guests

Paul Ehrlich, President, Center for Conservation Biology & Bing Professor of Population Studies, Stanford University

Denis Hayes, President & CEO, Bullitt Foundation & Earth Day Organizer

Andrew Watterson, Chief of Sustainability, City of Cleveland

David Beach, Director, GreenCityBlueLake Institute