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Buildings white roof global warming

Published on October 21st, 2011 | by Zachary Shahan


White Roofs May Not Be Good for Climate, May Increase Global Warming (Shocker!)

October 21st, 2011 by  

white roof global warming

White roofs have been promoted as a simple, easy, “soft geoengineering” solution to help combat global warming for awhile now. The solution has gotten the strong backing of former president Bill Clinton and current Energy Secretary Steven Chu. I thought this was a rather obvious solution we should adopt — reflect more back into space with lighter roofs. Many thought is was a good idea.

However, new research has flipped this white roofs solution into a potential global warming problem (showing that even the simplest geoengineering solutions may have side-effects we didn’t think up from the start). The study, led by Mark Z. Jacobson, a professor of civil and environmental engineering at Stanford University, found:

Jacobson’s computer modeling concluded that white roofs did indeed cool urban surfaces. However, they caused a net global warming, largely because they reduced cloudiness slightly by increasing the stability of the air, thereby reducing the vertical transport of moisture and energy to clouds. In Jacobson’s modeling, the reduction in cloudiness allowed more sunlight to reach the surface.

The increased sunlight reflected back into the atmosphere by white roofs in turn increased absorption of light by dark pollutants such as black carbon, which further increased heating of the atmosphere.

Now, one thing Jacobson’s team didn’t include in the study was how much white roofs reduced demand for electricity (and, thus, burning of fossil fuels). Of course, white roofs would also mean a house in a cold climate would need more heating in winter, but it’s not clear which way the benefit is stronger.

Summary points:

  1. Looks like we shouldn’t go painting everyone’s roof white after all (at least not until more research is done).
  2. Geoengineering (even “soft” options) will have more than the obvious or targeted effects.
  3. The best way to address global warming is still to just cut our burning of fossil fuels (vie basic energy efficiency or switching to clean energy options).

In Jacobson’s words: “There does not seem to be a benefit from investing in white roofs…. The most important thing is to reduce emissions of the pollutants that contribute to global warming.”

Solar PV Panels Help (in Multiple Ways)

Now, solar PV panels help address global warming in even more ways now, the study pointed out.

Aside from using sunlight instead of fossil fuels to create electricity, they shade one’s house (helpful in warmer climate, at least), and they don’t reflect sunlight back into the air like white roofs do.

Photo Credit: Attribution Some rights reserved by Walmart Stores

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About the Author

Zach is tryin' to help society help itself (and other species) with the power of the word. He spends most of his time here on CleanTechnica as its director and chief editor, but he's also the president of Important Media and the director/founder of EV Obsession and Solar Love. Zach is recognized globally as a solar energy, electric car, and energy storage expert. He has presented about cleantech at conferences in India, the UAE, Ukraine, Poland, Germany, the Netherlands, the USA, and Canada. Zach has long-term investments in TSLA, FSLR, SPWR, SEDG, & ABB — after years of covering solar and EVs, he simply has a lot of faith in these particular companies and feels like they are good cleantech companies to invest in. But he offers no professional investment advice and would rather not be responsible for you losing money, so don't jump to conclusions.

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  • Smenon

    The recent paper by Stanford’s Mark Jacobson and John Ten Hoeve (2011) on urban heat islands and cool roofs is a useful contribution to the literature. However, their results regarding white roofs are preliminary and uncertain. Along with our own work at the Lawrence Berkeley National Lab, other published papers have addressed the broader benefits of white roofs. In our view, these studies taken together raise important issues that need to be considered from a policy standpoint to fully understand the potential of more reflective (white or cool) surfaces.

    Jacobson and Ten Hoeve note that reflecting light from white roofs may lead to a decrease in cloud cover, thereby increasing, not decreasing, the urban heat effect. But they also note that their findings might change if they used different models. This is an ongoing research area not only for their group, but others, and ours as well. The findings should not be considered settled.

    We have found that white roofs do provide a low-cost solution that can help buildings reduce energy costs, in a wide variety of climates, as well as cool the atmosphere regionally and globally. We have also found disadvantages. The reflective roofs may cause unwanted glare, for example, and may modestly increase heating costs in winter. But answers to these issues are exactly the ones we’re working hard to find.

    Our work has shown that reflective roofs can lead to better air quality, reduce the strain on our electrical grid, improve comfort and decrease emissions from power plants. These are important considerations when evaluating all the available research.

    In our opinion, all of these arguments and studies suggest that selective use of white and other reflective roofs makes sense as part of an integrated strategy for more sustainable human existence on Earth. But the potential benefits offered by cool roofs do not diminish the need for sustained reductions in greenhouse gas emissions to control global climate, or the need for increased use of renewable energy sources.

    It’s important for the public to understand that scientific debate leads to better science. But it’s also important that the public receives—and the news media delivers—a message that properly conveys research news with all its many caveats and cautions. It’s not settled, until it’s settled.

    For more information, go to: http://heatisland.lbl.gov/news/cool-roofs-and-global-cooling-heat-island-group-responds-jacobson-ten-hoeve-2011

    Surabi Menon and Ronnen Levinson
    Berkeley Lab Heat Island Group

    • Anonymous

      Thanks for the note! Very helpful. Will updated the post a bit.

    • Anonymous

      I’m not seeing any disagreement between what your group and Jabobson’s found. Both find that white roofs can help keep individual buildings cooler. If that is the case and electricity for cooling is being generated close enough to the test area and from fossil fuels then it should be expected that air condition would be effected. Or it could be (also be) caused by the increased air stability that Jacobson found.

      The important finding by Jacobson is that white roofs are not cooling urban areas. That’s aside from the temperature of individual buildings. Perhaps you could plow through your data to see if you can collaborate.

      Mark has been concentrating on the role of soot (black carbon) in the atmosphere lately. That seems to be a factor largely overlooked by several/many researchers. He’s turned out an interesting paper on the role of atmospheric black carbon on Arctic ice melt.

      Of course, the first paper on a new finding should be considered “interesting”, but before a new finding is accepted it should be confirmed a few times.

      If your data doesn’t agree perhaps the two groups could meet at the fifty year line during The Big Game and duke it out…. ;o)

      • austin

        Thanks for this article. Got me started on a semester-long ethics paper.

  • Douglas Prince

    Damned if you do, damned if you don’t.

  • Amy Jordan

    You mean vetted-and-peer-reviewed-foot-kissy Chu couldn’t figure out that white is a reflective color??
    And that that MIGHT do something to the atmosphere in large quantity?
    Deserts full of reflective sand just wasn’t a good enough example?

    Well kids, here’s an easy comparison we can all try at home:

    Step 1) Go into a room with a bright light & turn the light on. So far so good, eh?
    Step 2) Put on a dark hat with a wide brim. Don’t fold the brim up any further than you need to see straight in front of you, a.k.a. leave some overhang in front.
    Step 3) Now, put on a white crewneck shirt and stand under the light while looking in the mirror. You should be able to see reflection of the light off of your shirt onto your neck area & the underside of the hat brim.
    Step 4) Go put on a black or otherwise dark crewneck shirt, one that’s not faded, and repeat Step 3 for comparison.

    Or, you could skip all those steps and just lay a white piece of paper or cloth on a flat surface, shine a light on it and hold your hand palm down about 6 inches over it, tilted up so you can see the light reflecting on your palm. Repeat with a dark piece of material, and you’ll see the difference.

    Rocket science, isn’t it?

    I think people would do well to recall the early motif of the “mad scientist” more often instead of the current trend of treating them like some sort of untouchable shamans. A study came out this year that showed scientists are bigger tax cheats than lawyers—what does THAT tell you?
    Many of them are competing for very lucrative grant money.
    I can’t think of much that people won’t do for money, can you?
    Especially those involved in politics.

    • Anonymous


      Did you read the article? Seems like you might have gotten no further than the title and noticing “Chu” before starting your rant….

      • Amy Jordan

        Did you read my response, or do you typically go all “reactionary” when your favored worldview gets pwned?

        • Anonymous

          Yes, I did read it.

          And my first response to you holds. Try reading the article, and concentrate. There aren’t many big words, you can look them up.

  • Anonymous

    “Of course, white roofs would also mean a house in a cold climate would need more heating in winter, but it’s not clear which way the benefit is stronger”

    If a house is gaining heat from sunlight on the roof in winter, it doesn’t begin to have enough insulation under the roof.

  • “Of course, white roofs would also mean a house in a cold climate would need more heating in winter, but it’s not clear which way the benefit is stronger”

    In the Energy Modeling training I have received I was taught that it takes more energy to cool a house than to heat a house. Simple Example: Central Air System has 2 fans- 1 on the AC Unit outside and 1 in the furnace.

    There is also the Heat Island Effect that the author did not consider…

    Does the Author work for the Fossil Fuel Industry?

    • Anonymous

      Did you read the article? It’s about Mark Jacobson’s research on urban heat islands.

      Jacobson is a Professor of Civil Engineering at Stanford and a major researcher in renewable energy and climate.

      As has been pointed out, there may be places where the lightness of the roof might aid the heating or cooling energy requirements. Your example falls flat in climates where cooling requirements are minimal. My house, for example, has nor needs no AC.

      • Anonymous

        ditto & ditto

  • Paul

    Speaking of the North, wouldn’t this just be replacing the solar reflection lost with melting arctic ice cover?

    • Anonymous

      Nope, and that’s the surprising thing about this finding.

      It also turns out that a cold air inversion over the Arctic is bad for ice formation. It traps heat being given off by the warmer water.

      Common sense can lead one astray….

  • “There does not seem to be a benefit from investing in white roofs…. The most important thing is to reduce emissions of the pollutants that contribute to global warming.” He answered his own question, by reducing cooling loads with in buildings with white roofs as this article states, which is the single largest energy consumer of the largest sector that emits carbon. So we still have a net reduced GW potential with white roofs. Right?

    • Anonymous

      I think the take-home here is that making all roofs white will not create an albedo effect and bounce light/heat back into space. Many had been counting on white roofs to be an effective and benign geoengineering tool.

      Whether an individual building might be able to cut its electricity needs via a white or dark roof is valid, but something different. It’s not geoengineering, but potential energy savings.

      We need a thousand knives to slay the beast. The better we understand which knives work and how best to use them the more effective we will be.

      • Anonymous

        Yep. It seems buildings in the north would probably benefit more from a black roof.. (but, again, that part of things still need to be studied more).

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