Hour 2: Cities and the buildings that inhabit them are a major source of greenhouse gas emissions. But some architects believe that fixes can be made to existing structures that will actually turn them into solutions to climate change and energy problems. We’ll talk about sustainable architecture this hour with Ed Mazria of architecture2030 and Thom Powell of Good, Fulton & Farrell. AIA Dallas hosts a discussion of sustainable architecture tonight at the headquarters of HKS Architects.