White roofs would offset warming, researchers say

White roofs would offset warming, researchers say
By Margot Roosevelt | Los Angeles Times
http://www.latimes.com/news/local/la-me-roofs10-2008sep10,0,2976609.story
September 14, 2008
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.

Since 2005, California 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 percent of the surface of most cities,
and pavement accounts for about 35 percent. 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 how to offset a rapid
growth in emissions, installing cool roofs and pavements would account
for more than 10 years of emissions growth, even without slashing
industrial pollution.

Akbari's paper, "Global Cooling: Increasing World-wide Urban Albedos
to Offset CO2," to be published in the journal Climatic Change, was
written with his colleague Surabi Menon and University of California,
Berkeley physicist Arthur Rosenfeld, a California energy commissioner.
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
pavement. "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."