white roofs energy equivalent of taking 300 million cars off road, DOE study says

[one...two...tree 2,762]

Roofs and pavements cover 50 to 65 percent of urban areas, and most of them are energy-absorbing black or another dark color. The problem? Those roofs and roadways collectively create what is called the “urban heat island effect” — that is, when a city is measurably warmer than rural areas nearby.

Are reflective white roofs the answer?

Yes, according to a new study. Researchers at the Lawrence Berkeley National Laboratory say that implementing cool roofs and cool pavements in cities around the world can actually make enough of a difference to cool the world.

A quick science lesson: white roofs reflect more of the sun’s rays than black ones, which absorb more of the energy as heat.

The benefits:

• Buildings with white roofs stay cooler.
• Air conditioned buildings with white roofs need less (and thus less energy) to stay cool.
• The heat absorbed by a black roof heats both the building and the air around it.
• Black roofs also radiate energy directly into the atmosphere, which is absorbed by clouds nearby. Trapped by the greenhouse effect, it contributes to global warming.

Better still, white roofs could cancel the greenhouse gas effects of up to two years of worldwide carbon dioxide emissions.

That’s important because more than half of the world’s population now lives in cities — and by 2040, it’s predicted that 70 percent of the world’s population will be city slickers.

The researchers used a detailed globe land surface model from NASA’s Goddard Space Flight Center to find the answer. At their fingertips: regional information on surface variables, such as topography, evaporation, radiation, temperature and cloud cover.

The researchers estimated improvement conservatively, and increased the average albedo, or solar reflectance, of all roofs by 0.25 and of pavements by 0.15.

(In other words: they didn’t assume that a black roof, which has an albedo of 0, would be replaced by a pure white roof with an albedo of 1 — just that it would be of a cooler color.)

The scientists found that, for northern hemisphere summers, increasing the reflectivity of roof and pavement materials in cities with a population greater than 1 million would achieve a one-time offset of 57 gigatons — that’s 1 billion metric tons — of CO2 emissions.

That’s a big deal, since worldwide CO2 emissions in 2006 were 28 gigatons. (The split, by the way: Thirty-one gigatons from roofs and 26 gigatons from pavements.)

In a statement, Berkeley Lab physicist Art Rosenfeld elaborates:

If all eligible urban flat roofs in the tropics and temperate regions were gradually converted to white, and sloped roofs to cool colors, they would offset the heating effect of the emission of roughly 24 gigatons of CO2, but one-time only. However, if we assume that roofs have a service life of 20 years, we can think of an equivalent annual rate of 1.2 gigatons per year. That offsets the emissions of roughly 300 million cars for 20 years.

Still, the researchers warn that it’s not a remedy to reverse the effects of the Industrial Revolution.

“Two years worth of emissions is huge, but compared to what we need to do, it’s just a dent in the problem,” said study co-author and Concordia University professor Hashem Akbari in a statement. “We’ve been dumping CO2 into the atmosphere for the last 200 years as if there’s no future.”

This study is a follow-up to a 2008 paper (related presentation 1; related presentation 2; both .pdf) published in the journal Climate Change, which found that implementing cool roofs and pavements worldwide could offset the effects of 44 gigatons of CO2 emissions.

http://www.smartplanet.com/blog/smart-takes/cool-cities-white-roofs-energy-equivalent-of-taking-300-million-cars-off-road-doe-study-says/9249

[I AM NOT THAT GUY 5,715]

That's a fact, Jack! I am familiar with roofing materials being in the RV industry. White materials keep the units cooler, and as a big plus, the materials last longer, since they reflect, instead of absorb heat and radiation. When I re-roofed my place, I went for the whitest material I could find. Only bad news: All the nearby overlooking vegetation seems to grow faster now.

[Ban Hammer 13,352]

is this supposed to be news? i knew about lighter roofs being better at least 3 decades ago.

[one...two...tree 2,762]

is this supposed to be news? i knew about lighter roofs being better at least 3 decades ago.

You knew 30 years ago, that converting to white roofs would be equivalent of taking 300 million, modern era cars off the road? Okay, Nostradamus.

[I AM NOT THAT GUY 5,715]

You knew 30 years ago, that converting to white roofs would be equivalent of taking 300 million, modern era cars off the road? Okay, Nostradamus.

Nobody really cares about such suspect equivalencies, but sensible and observant people can figure out the difference between light and dark colors, although an "Energy Expert" that gave my mother a "free" taxpayer subsidized energy evaluation convinced her that a black roof in Southern California would be more efficient in the long run back in the Carter daze. Hippies! Jeez!

Edited July 23, 2011 by Some Old Guy

[Ban Hammer 13,352]

You knew 30 years ago, that converting to white roofs would be equivalent of taking 300 million, modern era cars off the road? Okay, Nostradamus.

didn't say that, did i?

and your 300 million autos is based on the modeling, and we know how accurate that is - just check your local forecast for what's gonna happen 2 weeks from now.

[Mr. Big Dog 10,747]

You knew 30 years ago, that converting to white roofs would be equivalent of taking 300 million, modern era cars off the road? Okay, Nostradamus.

I think my now almost five year old daughter knows that it feels better on a sunny summer day wearing a white t-shirt than wearing a black t-shirt. Which is to say, it doesn't take a scientist to figure out that lighter colors keep you cooler when exposed to sunlight.

[Karee 4,190]

Most school buses around here now have white roofs.

[Bad_Daddy 2,209]

Thank god for white roofs.

[I AM NOT THAT GUY 5,715]

Thank god for white roofs.

Unless it's two feet of snow.

[Obama 2012 1,714]

Unless it's two feet of snow.

[dalegg 143]

I think my now almost five year old daughter knows that it feels better on a sunny summer day wearing a white t-shirt than wearing a black t-shirt. Which is to say, it doesn't take a scientist to figure out that lighter colors keep you cooler when exposed to sunlight.

5 years. Wow how time flies.

[Darnell 8,478]

You knew 30 years ago, that converting to white roofs would be equivalent of taking 300 million, modern era cars off the road? Okay, Nostradamus.

Yup - painting mobile homes with white insulating paint was big business, 30 years ago. So prevalent, could actually read newspaper advertisements about it.

[Mr. Big Dog 10,747]

5 years. Wow how time flies.

Tell me about it. Pre-school starts next month.

[I AM NOT THAT GUY 5,715]

Tell me about it. Pre-school starts next month.

Almost time to start cleaning that rifle, for when she starts dating.