Energy Secretary Chu: Paint roofs white to fight global warming

I have been pushing white or reflecting roofs as the lowest cost climate strategy (see “Geoengineering, adaptation and mitigation, Part 2: White roofs are the trillion-dollar solution“).  Indeed, it is almost certainly the single cheapest of the 12 to 14 wedges needed to stabilize near 2°C total warming — the equivalent to taking the world’s approximately 600 million cars off the road for 18 years, while quickly paying for itself in direct energy savings!


[100 m2 (~1000 ft2) of a white roof, replacing a dark roof, offsets the emission of 10 tonnes of CO2.]

So I was delighted when a reader sent me this amazing Agence France-Presse story from Tuesday:

US Energy Secretary Steven Chu said Tuesday the Obama administration wanted to paint roofs an energy-reflecting white, as he took part in a climate change symposium in London.

The Nobel laureate in physics called for a “new revolution” in energy generation to cut greenhouse gas emissions.

But he warned there was no silver bullet for tackling climate change, and said a range of measures should be introduced, including painting flat roofs white.

Making roads and roofs a paler colour could have the equivalent effect of taking every car in the world off the road for 11 years, Chu said.

It was a geo-engineering scheme that was “completely benign” and would keep buildings cooler and reduce energy use from air conditioning, as well as reflecting sunlight back away from the Earth.

I would add that by reducing the urban heat island effect (along with shade tree planting), white roofs are also the lowest cost “adaptation” strategy, directly cooling a city.  So it is perhaps the one true triple play in climate — mitigation, geo-engineering, and adaptation — that is also both low-cost and scalable.

For people who found white hard on the eye, scientists had also developed “cool colours” which looked to the human eye like normal ones, but reflect heat like pale colours even if they are darker shades.

And painting cars in cool or light colours could deliver considerable savings on energy use for air conditioning units, he said.

Speaking at the start of a symposium on climate change hosted by the Prince of Wales and attended by more than 20 Nobel laureates, Chu said fresh thinking was required to cut the amount of carbon created by power generation.

He said: “The industrial revolution was a revolution in the use of energy. It offloaded from human and animal power into using fossil fuels.

“We have to go to a different new revolution that can severely decrease the amount of carbon emissions in the generation of energy.”

Since I have been writing about white roofs and urban heat island mitigation (UHIM) for a long time, the readers who sent me this clip wrote:

Chu and Obama are listening to you on this!

While I suppose that’s possible — I’m told people at DOE and the White House do read this blog — in fact there is a far more plausible explanation.  The person who introduced me to white roofs and UHIM more than a decade and a half ago, the person with whom I co-authored numerous articles on this subject — including this 1997 Technology Review overview article, “Paint the Town White-and Green” — is California Energy Commissioner Art Rosenfeld.

Rosenfeld co-developed this whole new geo-engineering analysis with Lawrence Berkeley National Laboratory’s Hashem Akbari.  You can read their non-technical summary, “White Roofs Cool the World, Directly Offset CO2 and Delay Global Warming.”  And Rosenfeld is a friend of Chu’s, which is no surprise since they are both (brilliant) physicists and former LBNL scientists who focus on energy energy issues.

But provenance aside, if the U.S. Energy Secretary is publicly advancing white/reflective roofs at an international meeting, that means you can expect serious national and even international action on this important climate strategy.

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31 Responses to Energy Secretary Chu: Paint roofs white to fight global warming

  1. Modesty says:

    OK, whoa!

    Back in January, you thought using the word “offsets” here was “dumb” (or at least that the the word was dumb, in this context).

    So, since the word is even more loaded now: offsets in what respect, Joe?

    The roofs may be qualified for a one-time radiative forcing offset, but they could never take the place of actual CO2 cuts.

    [JR: I don’t follow you. This isn’t an “offset” — it is a direct, measurable impact. It is a “temporary” wedge, as I explained, that might last 4 decades, but no different than, say, a wedge of wind or efficiency, which also must be replaced when the technology reaches the end of its lifetime.]

  2. K L Reddington says:

    Actually the coatings industry is loaded with VOC’s Volatile organic compounds are the solvent vehicle that carries the colorant in paint. We are going to water based coatings and have a long way to go. No the roof is a consumer of CO2. The labor, shipping, application and equipment applied to the new paint job explain why the bid was probably in the millions mus the helicopter shot to take pictures.
    I only ordered one boat in my life with a non white deck. It is too hot to walk on a gelcoat surface barefoot other than white. The other advantage iswhite coatings require less UV inhibitors.

    Polyester degradation is affected by solar radiation, photocatalytic admixtures, water and moisture, chemicals, oxygen, ozone, temperature, abrasion, internal and external stress, and pigment fading.3 Out of all these, the following factors, all present in outdoor weathering, are the most important to coating degradation: moisture, elevated or lowered temperatures, oxidation and UV radiation.

    Hydroxyphenylbenzotriazole and the hydroxybenzophenone are 2 common UV inhibitors the diminish UV degradation.

  3. Merrick says:

    Whilst having white roofs seems like an obvious and simple strategy in hot climes (where you’re not having passive solar on the roof, that is), we need to loudly divorce this from the idea that it should be part of a package of albedo enhancement measures that take the place of carbon cuts.

    Those wacky geo-engineering advocates think if we only reflect enough sun (plant shinier crops! cover deserts in plastic!) then we don’t need the cuts. Even if they were right about temperature, it would mean increasing atmospheric CO2 content. That would acidify oceans, making shelled animals unable to form shells, and thus take big sections out of the food chain.

  4. Sasparilla says:

    It’d be great to see some national/international action on this as well. Every little step will help and the earlier the better.

    Great news to see this is being talked about at the highest levels, thanks for putting this up Joe.

  5. paulm says:

    Had to chuckle at the juxtaposition of these two articles in the

    China puts its faith in solar power with huge renewable energy investment
    By 2020, Chinese government is committed to raising the share of ­renewable energy ­in the energy mix to 6%

    White roofs and ‘cool’ cars – Obama’s US energy secretary gives Prince Charles tips on tackling climate change
    Reflecting sunlight on buildings and cars among dozens of ideas considered by Steven Chu and the US energy department

  6. Gail says:

    In the context of this disturbing analysis from the Guardian,, the white roof scheme smacks of desperation. It’s a sensible thing to doubt, but in the grand scheme of things not exactly where I would prefer to see our top energy czar lavishing his attention.

  7. Gail says:

    I meant “no” doubt.

  8. White roofs in conjunction with solar panels on top do cool the solar panels so boosting their efficiency by up to 15%, but white roofs OR solar panels?

    Solar panels will do far far more to lower CO2 which is the real prize, heat islands are just part of it.

  9. Zammy says:

    Sheep are white, so they should get a carbon credit for that.

    Why don’t we pour white paint into the oceans to make them white instead of blue?

    I mean, when it comes to climate change, “anything goes”, right?

    [JR: When it comes to avoiding catastrophic climate change, anything which measurably reduces emissions or warming at reasonable cost without causing more harm than good must be considered.]

  10. Rick Covert says:

    I remember when I lived in the Bahamas in the early to mid 1970’s that our first house had a white roof. Almost all of the houses had white roofs or Mediterranean style clay roofs. In Houston it’s the exact opposite. We changed from cedar roofs which were a fire hazard to tar shingle roofs. Fortunately our Mayor Bill White is aware of the problem but I’m wondering what it will take to get a city ordinance to change to white roofs. I know it would help my electric bill in the summer.

  11. JohnV says:

    I’m curious about the use of white roofs in a cooler climate. In many parts of Canada, air conditioners are rare so energy usage for summer cooling is minimal. Winter heating is where we use our energy, particularly since A/C is way more efficient than a gas-burning furnace.

    It seems to me that cities in cold climates should stick with black roofs to stay warm. Does that make sense?

    [JR: White roofs make sense in Chicago. Any place where there is a significant AC. Other places are relatively indifferent. You should have a huge amount of insulation in your attic in Canada, so the roof color should be secondary.]

  12. For some of California Energy Commissioner Art Rosenfeld’s presentations and papers, including those on white/cool roofs, please see:

    He has been a pioneer in energy efficiency technologies for many years.

    In 2005, Rosenfeld won the Fermi Award, “a Presidential award that honors scientists of international stature for lifetime exceptional achievement in the development, use, or production of energy.”

    The Fermi Award citation says, in part:

    “In 1985, recognizing that the solar reflectance of hot, dark roofs and pavements raised electricity demand for air conditioning by 20 percent in the summer (as well as increasing smog), he co-founded, with Dr. Hashem Akbari of Lawrence Berkeley National Laboratory, the Heat Islands Research Project at LBNL, which has since conducted groundbreaking research on the potential for shade trees and cool roofing and paving materials to reduce the urban heat islands effect.

    “The group is now working with manufacturers of roofing and paving materials to develop cool colored pigments and roofing for both cars and buildings. Since 2005, the California new buildings energy efficiency standards have required that flat roofs shall be white. Sloping roofs (a more prominent feature of the architecture) can still be colored, but starting in 2008 they must use the new cool pigments. Florida and Georgia now require cool roofs, and other states are beginning to adopt them as well.

    “Beyond technology development, Dr. Rosenfeld has been involved in formulating analyses and policies that continue to impact energy savings worldwide. He led the effort to develop “conservation supply curves.” These curves are now used worldwide, allowing straightforward comparisons of both the cost and the quantity of conservation with those of new energy supplies.”

  13. Sue Sturgis says:

    My husband and I just replaced our old black asphalt-shingle roof with a white one in hopes of staying cooler in the North Carolina summer, especially since we don’t use air conditioning. Question: Does our new roof qualify for any federal tax benefits?

  14. Bill R says:

    I want to second John V’s Question… it does seem that white roofs are a simple and relatively harmless “geoengineering” solution, but it seems that in cooler climates that get some sun in the winter that the benefit might be offset in CO2 terms by the lost absorbed energy that could offset heating costs. Of course if you are insulated well, that might not be true. Seems like there are some offsetting forces at work here potentially?

  15. John Mashey says:


    1) Why do yoiu think Chu isn’t worried about other things?

    2) Do you have some problem with him publicizing important work spearheaded by an old colleague of his at LBNL?

    This is the sort of long-hanging fruit that:

    a) Doesn’t need much, if any new technology.

    b) Doesn’t need big government funding.

    c) Can be done by:
    – Tweaking building codes sensibly, like we’ve already done here in CA
    – Using light paint where geographically sensible, when updating buildings

    d) Simply needs numerous people to understand there is value in doing this.

    e) Even saves money

    But you denigrate Chu for using his bully pulpit to talk about this?

    Can you explain why you do that?

  16. Gail says:

    John, did you read the article I linked to? That’s why. Basically I worry that the magnitude of the problem gets a bit lost if political ideology is allowed to dictate policy. Clearly Dr, Chu understands what needs to be done. The question is, does he possess the ability to stand up to the dark forces and do what needs to be done
    (assuming it’s even possible)?

  17. Sue, yes, reflective roofing is eligible for the 30% Federal Tax Credit just like all e3fficiency measures are now, including obviously solar and otherrenewable energy to replace your home fossil fuel use like electricity – but oddly it stil has a limit – I think it is $2,000:

  18. Modesty says:


    “This isn’t an “offset”.”

    Close to the top of the page you have an image (not working currently), cool-roofs, with the caption: “[100 m2 (~1000 ft2) of a white roof, replacing a dark roof, offsets the emission of 10 tonnes of CO2.]”

    This “offsetting” is due to the albedo change, the difference in radiative forcing and does not–and I’m not suggesting this is news to you–take into account the energy efficiency aspects of the white roof.

    As per the original article:
    “Changing albedo of urban surfaces and changing atmospheric CO2 concentrations both result in a change in radiative forcing. In these calculations, using the existing data, we will first estimate the increase in radiative forcing from increasing the atmospheric CO2 by 1 tonne (Section 5). Then through a simple model, we estimate the decrease in radiative forcing by increasing the albedo of roofs and paved surfaces in the urban areas (Section 6). A simple comparison of these two radiative forcings
    allows us to relate the changes in the solar reflectance of urban surfaces to the changes in the atmospheric CO2 content.”

    I’m not (at all) saying the effect is not measurable, and while I haven’t looked in detail at the assumptions in the radiative forcing calculations, I’ll be happy to grant the validity of those for the sake of argument.

    My point is that talking about this negative radiative forcing “offsetting” a certain amount of CO2 is not a good idea. For instance, as a commenter pointed out in January, this aspect of the white roofs does nothing to stop the acidification of the oceans (although the energy efficiency part of course does).

    “Installing cool roofs and cool pavements in cities worldwide does not require delicate international negotiations about capping CO2
    emission rates.”

    Keep on saying that the roofs “offset” CO2 emissions, and let’s see how long it takes until these roofs show up in delicate international negotiations about capping CO2 emission rates.

    [JR: Let’s hope they do show up in international negotiations — this is an important strategy. Look, I put up with you even though you don’t use your real name or email in violation of general policy here. But this ain’t an offset — and nobody here has proposed it as the solution to global warming, gimme a break. This ain’t the website to attack straw men.]

  19. AVE_fan says:

    The Chu recommendations for whiter roofs are most applicable in larger southern urban areas where there is a significant “heat island effect”. Here, the cumulative effect of solar radiation absorption throughout the day and season, increases the local temperature significantly beyond that which would occur in a small town at the same latitude under similar climactic conditions. The increased heat load in buildings causes demand for A/C to increase, creating even more (outside) heat which remains trapped by buildings and greenhouse gases.

    A number of options occur here to either mitigate or otherwise deal with the problem:

    1) Keep roofs as they are and cause the heat to be carried via air currents to converge at the base of Atmospheric Vortex Engines, distributed evenly throughout the urban area. Using this device, approximately 20% of the “excess heat” can be recovered as electricity to power A/C systems. The influx of cooler air from the countryside would also reduce the total A/C load slightly. The earth’s energy budget would be improved by allowing the heat to radiate to space from above the cloud level and above the greenhouse blanket (

    2) Instead of modifying the roofs themselves, install lightweight structures on top of them to either reflect the radiation or convert it to electricity. I could envision a series of slowly rotating parallel panels that reflect radiation at certain hours of the day, absorb it (as PV) during other hours, and allow gaps for radiation directly to space from the roofs during other periods.

    3) Train yourself to survive in a living hell for the day when the electricity and water stop arriving to your block in the city.

  20. David B. Benson says:

    Zammy — Are you going to slaughter all the black sheep then?


  21. Gail says:

    Anyone who has the technological background and clever ideas should go here:

    Is it exciting or terrifying that it has come the the National Academies soliciting geoengineering solutions to 1. reduce CO2 once it is emitted and 2. limit or offset the effects of greenhouse gasses??

  22. MarkB says:

    John V / Bill R

    I was curious about this too. Wikipedia has a fairly good well-sourced entry on this.

    I think the heat loss from reflective roofs isn’t that substantial in colder climates largely because the sun is lower in the sky during the winter months to begin with (for the same reason, solar panels generate more electricity in the summer), heating demand is highest in the evening (where the roof feature wouldn’t make a difference), and cool roofs help retain snow in areas of moderate snowfall, which provides some insulation.

  23. Omega Centauri says:

    It is silly to be concerned that short wave negative forcings (albedo enhancements) will cause ocean acidification. If we had sufficient albedo anhancements available to tolerate say 500ppm CO2, that would be a concern. But the albedo enhancements suggested so far would only shift the global temp versus CO2 concentration curves by a few ppm. They may be a cost effective BB, but no-one serious would consider them as a silver bullet. But, as most energy/climate experts think we need a whole stack of BB’s, we got to collect as many of them as we can.

    Incidentally, I’ve tried highly diluted outdoor paint (less than one part per hundred of paint), as a concrete cleaner. It makes older concrete look newer -by raising the albedo several percent. I suspect this technique could very cheaply make some modest difference, and you could probably use a street sweeper to apply it at very low cost.

  24. Thank you Gail. I made 2 suggestions so far.

  25. Gail says:

    Well, I concede. If Sara Palin is against it, it must be an absolutely brilliant idea!

  26. Modesty says:

    Omega Centauri:

    Who is talking about (anyone talking about) this being a silver bullet? Just cause Joe says:

    nobody here has proposed this as the solution to global warming…don’t attack strawmen…

    doesn’t mean that anyone WAS SUGGESTING that anyone (here) HAD proposed this as the “the solution to global warming” (= silver bullet). I certainly did not suggest that anyone here, least of all Joe, had proposed this as “the” solution.

    Where did THAT idea come from? Probably from my silly attempt to shoehorn my point into a paraphrase of a Prince song (may be qualified…never take the place…). So much for trying to be funny. Sorry about the confusion this caused. (But I certainly did NOT mean that anyone here had said that it COULD take the place of ALL or most CO2 reductions.)

    For the record:

    I think the white materials stuff is great, a no-brainer. Not that it matters, but I did say this in January.

    Geoengineering approaches that focus on the radiative balance obviously need to be considered, to stave off some warming (and this one carries benefits in two additional dimensions, hence the win-win-win), but I see no reason to talk about the albedo effect in terms of “offsetting” CO2 (no matter the potential size of these effects).

    Unless I misunderstood Joe in January, he seemed to agree that the pervasive use of the word “offsets” (as a verb) in the original article was unfortunate ( I believe he said it was a “dumb word”).

    Therefore, I was surprised to see the figure caption in the current post use this word.

    That’s all.

  27. Do you have any information about the impact of a white roof on the cooling bill of the building? If this can be quantified, could the carbon savings be quantified and sold as a carbon credit?

  28. The preferred alternative should always be green, i.e., vegetated roofs, wherever they are feasible. Green roofs provide greater cooling benefits, reduce building energy use, provide significant stormwater management benefits, and actively clean and filter the air and water. Although the up-front costs are higher than conventional roofs–and here is where tax incentives, tax credits, or public/private financing partnerships need to kick in–they more than pay for themselves over time through building energy savings and significantly longer lifespan. The data we have collected on our (American Society of Landscape Architects’) green roof shows how effective green roofs are at addressing multiple environmental issues. You can check it out on our website: Click on the “tour our green roof” link in the right column. All that being said, if a green roof is not feasible because of roof construction, the lighter colored roof is absolutely the right way to go.

  29. Lewis Perelman says:

    There seems to be chronic misunderstanding of the thermodynamics of roof color in cold/northern settings. Roof color affects not only how much radiation is absorbed but also how much is emitted. A dark surface will just as efficiently radiate heat energy in the dark, at night, as it absorbs radiation from light during the day. (At least in general; particular materials may radiate or reflect specific wavelengths differently.)

    Given that in high latitude locations there are more dark hours than light hours in the winter, a dark roof is prone to radiate as more heat energy out of a structure at night than it absorbs from sunlight during the day.

    This is so regardless of the amount of attic insulation. A well insulated attic obviously will reduce conductive heat loss. It also will equally reduce the amount of heat conveyed to living space from any energy absorbed by the roof during daylight hours. Any heat absorbed from the sun during the day still will be radiated away at night.

    Overall, the benefits of reflective roofs are the same in both hot and cold weather: they reduce the flow of heat energy across the envelope of a building. This is the same reason that a thermos bottle is useful both to keep a cold drink cold and to keep a hot beverage warm.

  30. Re my last, on further consideration, I have that wrong.

  31. Roger Capettini says:

    Is there any product that can be used at a reasonable cost — and which will produce the desired results — for changing the color of your shingle roof?

    [JR: “Energy Star” white reflective paint.]