Street Grids May Make Cities Hotter

In 1995, an unbearable heatwave in Chicago, with temperatures reaching above 100 degrees, killed an estimated 739 people. The extreme heat was in part a consequence of the urban heat island effect, which makes downtown areas ostensibly warmer than their surrounding suburban and rural areas. The difference is even starker at night: even as the temperature cools, the release of heat absorbed during the day by asphalt and densely packed buildings can make the downtown area some 20 degrees warmer in some cities.

By now, scientists know that the density of buildings, the absorption of light by those buildings, and the relative lack of vegetation in cities are major contributors to the urban heat island effect. It’s why cities like Chicago are hoping to find relief through green roofs and reflective construction materials, or through planting more trees and banning cars. In a more radical move, Los Angeles even began painting their roads white as part of Mayor Eric Garcetti’s effort to bring down the city’s temperature by just under 2 degrees over the next 20 years.