White roofs in Bermuda. The roofs are made from limestone and are built specifically to catch rainwater which is then used for drinking water. (NEWSCOM)
Study: white rooftops could curb climate change
By Eoin O'Carroll | 09.10.08
If the world’s 100 biggest cities were to whiten the roofs of all of their buildings and use more reflective pavement, the global cooling effect would be huge, a new study has concluded.
Speaking at the Fifth Annual California Climate Change Research Conference in Sacramento, Hashem Akbari, a physicist with the Lawrence Berkeley National Laboratory, said that he has created a formula to determine how much heat-trapping carbon dioxide would be offset by reflecting the solar radiation back into space. In his presentation [PDF], he said that replacing the dark shingles on a 1,000-square-foot roof – the average size of an American home – with white material would offset 10 metric tons of greenhouse gases.
His paper, “Global Cooling: Increasing Worldwide Urban Albedos to Offset CO2,” will be published in the journal Climatic Change.
While this may sound like greenwashing (but with whitewash), the potential savings here are huge. The LA Times walks us through the numbers:
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 industrial pollution.
The benefits of white roofs and reflective pavement extend beyond climate change. White roofs can cut air conditioning costs by 20 percent, according to California’s Energy Commissioner. And reflective surfaces would reduce what’s known as the urban heat island effect, that is, the capacity of metropolitan areas to absorb more heat than their surrounding areas. According to Mr. Akbari’s study, cooler temperatures would slow the rates of chemical reactions that produce smog.
It sounds like a foolproof plan, but Keith Johnson, the Wall Street Journal’s eco-blogger, is skeptical that we could pull it off:
[L]ike with most grand plans, the devil is in the details. In many places, local zoning regulations strictly dictate architectural styles, including roof colors. Where white roofs are allowed or even required, progress comes piecemeal. Since 2005, California’s had a building code that mandated white roofs for commercial buildings, and is currently beefing that code up to include other kind of roofs.
But even the Golden State’s environmental enthusiasm has limits—it can’t make black-topped roads white overnight. The scale and cost of any program that would re-top all the roofs and paved surfaces in cities the size of Los Angeles, Mexico City, New Delhi, and Tokyo simultaneously makes Al Gore’s plan to power America with 100% renewable energy in ten years seem cheap and doable by comparison.
Still, this doesn’t have to be an all-or-nothing proposition. If Akbari’s numbers are right, then converting 10 percent of the roads and rooftops of the world’s 100 largest cities would offset one year of emissions growth. Not too shabby.
That said, I’m not thrilled about the prospect of driving – or crossing a busy street – on a reflective surface. And not all of us get to live in sunny California. Sure, a white rooftop may cut my air-conditioning costs in the summer, but when winter comes, what will it do to my heating bill?
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2. Amanda | 09.11.08
“Sure, a white rooftop may cut my air-conditioning costs in the summer, but when winter comes, what will it do to my heating bill?”
I bet it will stay the same, after all, snow is white!
3. Alan Russell | 09.11.08
I think white roofs is very doable. The biggest problem is keeping them white.
I think white roads would be a real problem for most folks though, keeping them white would be nigh impossible and the blinding glare would probably cause some horrible accidents. But even making the roads 10% or 20% whiter would help. If you have ever walked along a grey road (vs a blacktop road) you know the difference.
4. Jul-Mar | 09.11.08
White Rooftops — the positive eco effect sounds good. Are there any “White Roof” Builders in North Carolina: Greensboro, High Point or Winston-Salem?
6. Andrew Gronosky | 09.11.08
Sherry Blair asks, “How would white roofs work with solar energy on the roof?” That’s an insightful question.
The solar collectors would have to be black, so that portion of the roof wouldn’t be reflective. However, using solar energy is an even better way to offset carbon emissions than having a white roof!
The best solution would be to use solar collectors to the extent possible, and white roofing material everywhere else. Most solar collectors only cover a portion of the roof’s surface.
7. Ronanki gopalakrishna | 09.12.08
The refleting roofs are established over number of years, many types of reflctive paints on commercial names as Heat Shield are availble when painted last for long years. They also avoid the water leaks and work as insulators during the winter. This is well estblised to avoid entry of heat in the top floor
Best Wishes
ronanki
8. Jordan Woods | 09.12.08
“And not all of us get to live in sunny California. Sure, a white rooftop may cut my air-conditioning costs in the summer, but when winter comes, what will it do to my heating bill?” Probably still save you money, actually. It’s a common misconception that white loses heat quicker than black. If you look into thermodynamics, black absorbs and radiates heat the quicker, while white absorbs and radiates the slowest. So, while your roof may be absorbing less heat from the sun, you’ll also be losing less to the surrounding environment.
10. Karen Anne | 09.13.08
If you have a nearly new dark roof of regular shingles, is there any way to make it whiter without replacing it? Such as a durable coating?
11. Judy | 09.14.08
What’s the difference in the environmental impact of white roofs (assuming there’s a way to keep them white) and green roofs, which are growing things?
12. Samer | 09.19.08
Do you know of any address that supplies plastic and fiber made white roof tops?
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1. Richard | 09.11.08
You asked, “a white rooftop may cut my air-conditioning costs in the summer, but when winter comes, what will it do to my heating bill?” Absolutely nothing. Attic spaces are ventilated and the sun is low in winter. You won’t notice any increase in heating costs in winter from a white roof. Mostly, it will make your roof last longer and drop summertime bills. There is no downside. Roofing material should be taxed based on albedo. The more reflective, the lower the tax.