Eighty percent of New York City's pollutants come from buildings and 20 percent from transportation. This is a reversal from most cities, which see pollution from transportation rather than high density buildings, explains New York's Mayor Bloomberg. The mayor is in Sao Paolo, Brazil for a meeting on climate change. "There's an awful lot that has to be done on a national and an international level, says mayor Bloomberg. "But at the same time, mayors are held accountable to deliver services and are trying to do things at a local level."