Can we afford eco-cities?

Durban, South Africa (CNN) -- Making cities greener "actually makes a lot of sense" in spite of the economic crisis, says former Irish President, Mary Robinson.

"You save money," she said, adding that the real challenge is greening cities in poorer nations, like Bangladesh, where people live in "almost impossible conditions."

Robinson was one of four leading climate change thinkers discussing how viable it is to invest in sustainable cities in a debate hosted by CNN's Robyn Curnow during the 2011 U.N. Conference on Climate Change last week in Durban.