By 2100, the UN estimates that the world's population will grow to just over 11 billion people. Architect Vishaan Chakrabarti wants us to start thinking about how we'll house all these people -- and how new construction can fight climate change rather than make it worse. In this visionary talk, Chakrabarti proposes a "Goldilocks" solution to sustainable housing that exists in the sweet spot between single-family homes and towering skyscrapers.