Los Angeles Times
September 10, 2008
To slow global warming, install white roofs
By Margot Roosevelt – Los Angeles Times Staff Writer
Builders have known for decades that white roofs reflect the sun’s
rays and lower the cost of air conditioning. But now scientists say
they have quantified a new benefit: slowing global warming.
If the 100 biggest cities in the world installed white roofs and
changed their pavement to more reflective materials — say, concrete
instead of asphalt-based material — the global cooling effect would
be massive, according to data released Tuesday at California’s annual
Climate Change Research Conference in Sacramento.
Since 2005, the Golden State has required that flat commercial
structures have white roofs. Next year, new and retrofitted
residential and commercial buildings, with both flat and sloped
roofs, will have to install heat-reflecting roofing, as part of an
energy-efficient building code.
But the state has yet to pass any rules to encourage cooler pavement
on its roads, which are largely coated with heat-absorbing asphalt, a
cheap byproduct of oil refining.
According to Hashem Akbari, a physicist with the Lawrence Berkeley
National Laboratory, a 1,000-square-foot roof — the average size on
an American home — offsets 10 metric tons of planet-heating carbon
dioxide emissions in the atmosphere if dark-colored shingles or
coatings are replaced with white material.
Globally, roofs account for 25% of the surface of most cities, and
pavement accounts for about 35%. If all were switched to reflective
material in 100 major urban areas, it would offset 44 metric gigatons
of greenhouse gases, which have been trapping heat in the atmosphere
and altering the climate on a potentially dangerous scale.
That is more than all the countries on Earth emit in a single year.
And, with global climate negotiators focused on limiting a rapid
increase in emissions, installing cool roofs and pavements would
offset more than 10 years of emissions growth, even without slashing
Akbari’s paper, “Global Cooling: Increasing Worldwide Urban Albedos
to Offset CO2,” to be published in the journal Climatic Change, was
written with his colleague Surabi Menon and UC Berkeley physicist
Arthur Rosenfeld, a member of the California Energy Commission. All
three have been associated with the laboratory’s Heat Island Group,
which has published extensive research on how roofs and pavement
raise urban temperatures.
Akbari and Rosenfeld said they will mount an effort to persuade the
United Nations to organize major cities to alter their roofing and
“I call it win-win-win,” Akbari said. “First, a cooler environment
not only saves energy but improves comfort. Second, cooling a city by
a few degrees dramatically reduces smog. And the third win is
offsetting global warming.”