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
Painting roofs white can cool cities. That’s what scientists discovered in a new study that used a computer model to examine how white roofs affect temperature.
"Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat," says scientist Keith Oleson.
Cities are affected more by global warming than rural areas. Roads, dark roofs and other surfaces in cities absorb heat from the Sun. This creates an urban heat island effect that can raise temperatures 2-5 degrees Fahrenheit (about 1-3 degrees Celsius) or more, compared to rural areas.
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.
The study team used a newly developed computer model to simulate the amount of solar radiation that is absorbed or reflected in cities. The model results indicate that, if every roof were painted white, the urban heat island effect could be reduced by a third.
This would cool the world's cities an average of about 0.7 F. There would be more cooling during the day, especially in summer. Cities in different areas of the world would have different amounts of cooling. New York City, for example, would cool in summer afternoons by almost 2 degrees Fahrenheit.
In the real world, the cooling impact might be somewhat less because it’s hard to keep a roof looking white. Over time the white paint may darken with dust and decay. Some parts of roofs, such as vents, can’t be painted white.
White roofs would also cool temperatures inside buildings. This would have an impact on the amount of energy used to heat and air condition the space. Since most of this energy usually comes from fossil fuels, which release heat-trapping greenhouse gases into the atmosphere, white roofs could affect the amount of global warming too.
Last modified February 19, 2010 by Lisa Gardiner.
Shop Windows to the Universe Science Store!
Our online store
includes issues of NESTA's quarterly journal, The Earth Scientist
, full of classroom activities on different topics in Earth and space science, ranging from seismology
, rocks and minerals
, and Earth system science
You might also be interested in:
The air in urban areas can be 2 - 5°C (3.6 - 9°F) warmer than nearby rural areas. This is known as the urban heat island effect. It’s most noticeable when there is little wind. An urban heat island can...more
Even though only a tiny amount of the gases in Earth’s atmosphere are greenhouse gases, they have a huge effect on climate. There are several different types of greenhouse gases. The major ones are carbon...more
Earth’s climate is warming. During the 20th Century Earth’s average temperature rose 0.6° Celsius (1.1°F). Scientists are finding that the change in temperature has been causing other aspects of our planet...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. "The data will help give us a better road map to what a future...more
The Earth's mantle is a rocky, solid shell that is between the Earth's crust and the outer core, and makes up about 84 percent of the Earth's volume. The mantle is made up of many distinct portions or...more
Some geologic faults that appear strong and stable, slip and slide like weak faults, causing earthquakes. Scientists have been looking at one of these faults in a new way to figure out why. In theory,...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