The "urban heat island effect" is the name for the phenomenon of densely populated urban areas having significantly higher temperatures than surrounding areas, reported DiscoveryChannel.ca Aug. 28. Concrete, which holds heat, is seen as a large contributor. Cities can combat the problem with green spaces – and increasingly green roofs. In Canada's biggest city, officials have proposed the Green Roof Pilot Program, which will showcase a variety of green roof types to encourage this type of construction in Toronto. York University, one of the largest institutions in Toronto, added a green roof to its computer science building in 2003.