A construction crew paints a white roof in downtown Washington, D.C.
Click on image for full size
Courtesy of Maria Jose-Vinas, American Geophysical Union
White Roofs May Successfully Cool Cities
News story originally written on January 28, 2010
Cities are affected more by global warming than rural areas. Roads, dark roofs and other surfaces in cities hold onto heat from the Sun. This creates an urban heat island effect that can raise the temperature in a city as much as 5 degrees Fahrenheit (about 1-3 degrees Celsius).
Scientists say that painting roofs white can keep cities cool. White roofs would reflect some of that heat back into space and cool temperatures, much like wearing a white shirt on a sunny day can be cooler than wearing a dark shirt.
They used a computer model to look at how white rooftops affect what happens to energy from the Sun that comes to Earth. Some of that energy is absorbed by the roof, which warms things up. Some of it is reflected back out to space.
Their model shows that, if every roof were painted white, cities would be almost one degree Fahrenheit cooler on average. Some cities would have more cooling than others. New York City would be almost 2 degrees Fahrenheit cooler on summer afternoons.
But it’s hard to keep a roof looking white. Over time white paint may look darker because of dust and decay. Some parts of roofs, such as vents, can’t be painted white. So there might not be as much cooling as the model predicts.
Shop Windows to the Universe Science Store!
Our online store
on science education, classroom activities in The Earth Scientist
specimens, and educational games
You might also be interested in:
Earth’s climate is getting warmer. During the past 100 years Earth’s average temperature rose about 0.6° Celsius (1.0° F). Things that people are doing like burning fossil fuels, changing the way land...more
It often feels a bit warmer in a city than it does in a nearby rural area. This is called the urban heat island effect. What makes cities warmer? Urban heat islands form because the buildings, roads,...more
Scientists have learned that Mount Hood, Oregon's tallest mountain, has erupted in the past due to the mixing of two different types of magma. Adam Kent, a geologist at Oregon State University, says this...more
The Earth's mantle is a rocky, solid shell that is between the Earth's crust and the outer core. The mantle is made up of many different reservoirs that have different chemical compositions. Scientists...more
Some faults look strong and like they wouldn’t cause an earthquake. But it turns out that they can slip and slide like weak faults causing earthquakes. Scientists have been looking at one of these faults...more
The sun goes through cycles that last approximately 11 years. These solar cycle include phases with more magnetic activity, sunspots, and solar flares. They also include phases with less activity. The...more
Studying tree rings doesn't only tell us the age of that tree. Tree rings also show what climate was like while the tree was alive. This means that tree rings can tell us about climates of the past. Two...more