Painting Your Roof White Doesn't Work

That's just one of the myths debunked in a new paper on the climate.

Painting roofs white has been--like changing lightbulbs--one of the well-cited easy ways out of climate change. By reflecting more light and heat back to the atmosphere, a white roof should act like a natural anti-warming device, while also reducing your energy costs by keeping your house cool in the summer. Turns out, painting your roof white would be simply a massive waste of white paint.

As it is, Mark Jacobson, a professor of civil and environmental engineering at Stanford and his colleague, research student John Ten Hoeve, found in a new paper in the Journal of Climate that while white surfaces cooled houses, they also reduced cloudiness, allowing more sunlight to reach the ground. That conclusion complements a recent study by the National Center for Atmospheric Research that found that the positive effect of white roofs in the summer would be offset by a negative effect in the winter. 

"There does not seem to be a benefit from investing in white roofs," says Jacobson. "The most important thing is to reduce emissions of the pollutants that contribute to global warming."

Solar panels are a better idea than white paint, he says. “The better thing to do is to put a solar panel on the roof because that not only cools the house by absorbing the sunlight to make electricity. It also offsets fossil fuel generation at power plants.”

Jacobson is similarly against other geo-engineering approaches, such as the idea of pumping tons of sulphur particles into the atmosphere to reflect light back into space. 

“With all geo-engineering approaches, you are not solving the problem but masking it. There are all kinds of consequences people are not aware of, and it doesn't solve the problem. You are still going to have all these greenhouse gases going into the air.”

Among other debunkings in the report: the finding that “urban heat islands”--the heating effect of covering vegetation with buildings and roads--may have as much impact on the climate as greenhouse gasses.

Heat islands are an attractive explanation for two reasons. One, nobody disputes that cities produce more heat than rural areas. Roofs and sidewalks absorb more sunlight than greenery, and reduce evaporation, lessening the natural cooling effect. Cities also see more human activity, producing heat from transport, air conditioning, and the like. 

Moreover, the effect of heat islands on climate change has been under-studied. Jacobson says until recently nobody had ever done research covering the global impact, including the impact of “feedbacks” between urban surfaces and the atmosphere.

But it turns out that since the Industrial Revolution only 2 to 4 percent of "gross" global warming has been caused by heat islands, while 79 percent can put down to greenhouse gasses, and 18 percent is due to "black carbon" (soot in the air that absorbs sunlight). 

“Two to 4 percent is small relative to other contributors. But people who are contrarian to global warming suggest that heat islands are responsible for a large part of global warming. This and sunspots are the main arguments of climate skeptics,” says Jacobson.

[Image: Walmart's Flickr stream]

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15 Comments

  • GeneralRoofing Canada Grs

    Newer research is available that shows in the southern states a reflective roof is a benefit and as you get closer to Canada a black roof is more net positive. Black vs. white depends on where you live.

  • Damursocute

    So Ben Schiller, what do you suggest will make a difference. I could afford a bucket of paint but I have no chance of paying for solar power. Can you also debunk the reality of how screwed we are? What in reality is going to change anything? Maybe if everyone did paint their roof white, symbolism or not.. we could effect collectively some change. Can you add to your article the scientific facts of what humanity is doing to our oceans, the effect of out populations growth rates... what do you suggest other than solar panels?

  • Jeffrey Stephens

    Okay, so as far as global warming is concerned, white roofs aren't that big of a deal. But what about for personal use? In Texas, I can EASILY see the benefit of a white roof. Lost cause because of the reverse effect in winter? AAAHAHAHAHAAA! WTF is winter? Too bad for HOAs, that won't let you do the right thing!

  • Says what

    I'm with you. Here in Texas I'm sure it would more than cover the costs. I'm sure at some latitude you could draw a line for its effectiveness, but surely the southern states could benefit.

  • Dave

    Can I just say you are wrong and short-sighted?  White roofs reduce heat in buildings and reduce air conditioning hours which reduces electricity load which reduces electricity production requirements which reduces the burning of gas or coal which polutes the atmosphere.

  • Fried brain.

     ok, so im curiouse if one of you science folks can help me understand better.

    -white = reflecting most waves from the sun (like the north and south poles)... This reduces cloud production in that area.
    I get that all of the uv rays are reppelled. but how would absorbing the heat on the roof increase  cloud formation.
    I thought that was the trees job to do all that stuff.

    Oh well, you guys now more (thats for sure), but in my mind, if reflecting as much energy away from the roof reduces the surface area & temp of a house- then it cant be all bad.

  • Rick Adlam

    This article is outdated. It depends what you paint the roof with, and whether you have hot summers or cold winters. From what I have seen, US winters are much colder than UK winters, let alone Southern Australian winters, or sub tropical Brisbane winters. But the US would have Southern States that this article is wrong for in my view.
     I put the CSIRO findings [A Government body] way ahead of any Uni.The CSIRO in Australia tested white paint with new nano particles recently and found it cooled the home in summers AND warmed it in winter, compared to a dark coloured roof new, from the manufacturer. So this article's premise is wrong IMO. Its not the colour, its the insulation and reflectance that's important.My personal experience in painting roofs 20 years ago, was that unpainted galvanised roofing was hot to work on, Too hot to wear black soled shoes and without gloves you would burn your hands touching the roof or tools. But once painted [three coat process] the roof was cool [actually cold] to touch on a 30C day. The owner thought I had insulated the roof cavity as well as coating the roof. After painting I always used a cross linked clear glaze. I did this in those days to make the roof self cleaning, but apparently this is also important for reflectance.And the reverse was true in winter. Bare galvanised iron radiated heat out of the home! Same with cement roof tiles. They also made the home damper in winter because of condensation.So coating these materials, cooled the home in summer, and warmed it in winter, due to the insulating effect of the coating!This article does not address the heat retention issue. My current home has cement tiles. On a hot day in subtropical Brisbane, Australia, the cement tiles are still radiating heat several hours after the sun have gone down. So you run air conditioning long after the outside air temperature is comfortable. Its like living in a brick lined pizza oven. Please note. We can have night minimum temperatures close to day time maximum temperatures in Brisbane.The CSIRO study also claims that cities with coated roofs would be cooler to walk in summer, so again, this article is wrong. One problem in global warming is heat retention of cities. [Cities are getting hotter]. Building can't retain heat if they don't absorb it in the first place. So the solar panels argument is misplaced.Yes solar panels are a good way to convert solar radiation to electricity, but that electricity will eventually be returned as heat as its used in air conditioners, refrigerators and lights.All these are reduced by insulating roof coatings [that work] And reflectance is more important than colour. That is your fridge works less when your home is cooler, and your lights are used less if you you white paints in the home, and if you design the home to use natural light better. Most builders don't understand that most of the heat comes from the bottom of the window and most of the light comes from the top of the window. [That is the higher your windows, the more the light is thrown into the room, and the lower the window the more heat that adds to thermal mass of the home. And glass emissiveness in windows is another big area for designers to look at.All these energy users can be reduced or eliminated completely by better home design or building design.Yes, reducing fossil fuels will stop the greenhouse effect. But what's wrong with a "belts and braces" approach? You'll be less likely to be caught with your pants down.

  • Sonya

    Sound like we'd be better off working on the 18% contribution of 'black carbon' or soot. That's pollution that's doing damage to people through poor air quality.

  • Sabrina Pooler

    Interesting article.  I think there are a few points that have been misunderstood and before jumping to conclusions saying that painting a roof white is pointless, this needs to be looked at from a different angle.  First look at the basics, when you put on a white shirt in the summer your cooler, when you put on a black shirt your warmer, right.  Everyone should have some experience with this.  When you paint a roof white it reflects the solar spectrum back into the atmosphere, including thermal energy.  When a roof is a darker color it has a lower albedo, or in other words, it doesn't reflect the solar energy as much, so it is in-turn warmer from thermal energy which also makes your building warmer.  

    The misunderstanding that I think is happening here is that if you paint urban cities roofs white, the reduction of the temperature of the heat island will have an impact on climate change.  This isn't going to have much of a significant change on climate in that aspect.  It is the reduction of energy uses specifically for climate control (AC) in buildings that will have an impact (reduction of about 20%).  Considering that we have a high density of population using energy in urban areas this also adds to the significance. But painting roofs white everywhere is not the idea for this white roof concept.  Only in areas that experience warmer climates and only on roofs that are flat or have a low surface slope will this have a significant impact on energy uses.  So yes, paint the roofs white in LA but don't paint them white in Montreal.  Some statistics say that up to 50% of natural disaster deaths happen due to urban heat waves, this for a human health standard, should be another reason to paint urban surfaces light colors to reflect heat back into the atmosphere, along with planting vegetation, but thats another story.  

    As far as a decrease of clouds due to white roofs, I am really not sure how this would happen.  Clouds occur when warm moist air reaches cool dry air and/or is pushed upward to its dew-point condensation level.  Perhaps that subject goes beyond my compression. I do not know what Jacobson's computer modeling system was either, and modeling is finicky at time.  Jacobson's modeling results said there would be a increase of temperature due to the increase of net solar energy reaching the earths surface.  Yup, that will happen if there are no clouds.  But compared to the heat that dark surfaces produce (up to 180 degrees F on dark rooftops) I strongly disagree that this will create a warmer atmosphere then if rooftops are about 100 degrees F (white roods).  And also if you consider if at night there is a continuum of no clouds, thermal radiation will leave the surfaces and go right back up into the atmosphere, it will not get trapped due to clouds and therefor the nights would be cooler.  

    I live in Spain where houses have been painted white for their reflective cooling properties for hundreds of years, and yeah, it works, no computer science behind it.  Twenty percent savings on energy compaired to 15% efficiency of a solar pannel?  I don't know...   

  • art

    we've been dumping greenhouse gases into the atmosphere for thousands of years
    and tons of it in the last century. we could be causing climate change,
    accelerating it, or just witnessing the earth's natural progression. the point
    is we can do something about it. whether it's "pumping tons of sulphur
    particles into the atmosphere or water vapor we must do something. we can
    not sit idle while thousands die and trillions of dollars of property is
    destroyed.

  • Blain Rempel

    Regardless of who is right or wrong on this specific topic, it's instructive that we can't even conclusively agree on the benefits (or not) of something as simple as this. Yet we're supposed to wholeheartedly embrace much more encompassing and impactful actions to prevent "global warming". Can't say as I have any faith we know what we're doing in either case.

    Heck, we can't even conclusively agree on more basic and easy to study / understand things such as if eggs or coffee are good or bad for a person.

  • Wize Adz

    White roofs, CFLs, and more efficient vehicles are low-hanging fruit when it comes to saving energy.  No, they're not enough to change the course of climate change, but they are cost effective (provided you stick to the established replacement cycle) and they are a good way to save both energy and money.

    We've got to start somewhere, and these are as good a place as any.

    Anyone who thinks that recycling a few aluminum cans or replacing a few light bulbs is going to change the course of history clearly doesn't understand how big the problem is.  And the people who stick their heads in the sand and pretend there isn't a problem are even worse.  Alas, as someone who has a handle on the problem, I don't have a handle on the solution -- sustainability is very difficult when you consider the energy, climate, environmental, ecological, financial, and social aspects of it.  But, despite being daunting, the whole picture is very interesting.

  • Tim

    This conflicts with LBL's study on cool roofs "Potential benefits of cool roofs on commercial buildings". This study found that the winter heating penatly was more than compensated for in energy reduction during the summer.

    The other issue with this report is that it does not address energy consumption or reduction of green house gasses resulting from lower energy use. It is very limited in scope.

  • Nearsited

    Probably saved a lot of time having a Warmist priest describe the rationale of the heretics. Quite professional.