UCAR: Roof white out helps UHI

I find it humorous thatUCAR had to resort to modeling to prove something that can be measured empirically. But then again this is UCAR, and they have a big computer at their NCAR office. Painting roofs white would probably help cool NOAA weather stations that are positioned on rooftops, like this one on the roof of the Santa Ana fire station in southern California, with surroundings that look a lot like the photo provided with the press release shown below. – Anthony

Santa Ana Station looking North.  Click for a larger image

Computer model demonstrates that white roofs may successfully cool cities

January 28, 2010

BOULDER—Painting the roofs of buildings white has the potential to significantly cool cities and mitigate some impacts of global warming, a new study indicates. The new NCAR-led research suggests there may be merit to an idea advanced by U.S. Energy Secretary Steven Chu that white roofs can be an important tool to help society adjust to climate change.

But the study team, led by scientists at the National Center for Atmospheric Research (NCAR), cautions that there are still many hurdles between the concept and actual use of white roofs to counteract rising temperatures.

painting white roofs

A construction crew works on a white roof in Washington, D.C. (©American Geophysical Union, photo by Maria-José Viñas. Reproduction permitted with credit.)

“Our research demonstrates that white roofs, at least in theory, can be an effective method for reducing urban heat,” says NCAR scientist Keith Oleson, the lead author of the study. “It remains to be seen if it’s actually feasible for cities to paint their roofs white, but the idea certainly warrants further investigation.”

The study is slated for publication later this winter in Geophysical Research Letters. It was funded by the National Science Foundation, NCAR’s sponsor.

Cities are particularly vulnerable to climate change because they are warmer than outlying rural areas. Asphalt roads, tar roofs, and other artificial surfaces absorb heat from the Sun, creating an urban heat island effect that can raise temperatures on average by 2-5 degrees Fahrenheit (about 1-3 degrees Celsius) or more compared to rural areas. White roofs would reflect some of that heat back into space and cool temperatures, much as wearing a white shirt on a sunny day can be cooler than wearing a dark shirt.

The study team used a newly developed computer model to simulate the amount of solar radiation that is absorbed or reflected by urban surfaces. The model simulations, which provide scientists with an idealized view of different types of cities around the world, indicate that, if every roof were entirely painted white, the urban heat island effect could be reduced by 33 percent. This would cool the world’s cities by an average of about 0.7 degrees F, with the cooling influence particularly pronounced during the day, especially in summer.

The authors emphasize that their research should be viewed as a hypothetical look at typical city landscapes rather than the actual rooftops of any one city. In the real world, the cooling impact might be somewhat less because dust and weathering would cause the white paint to darken over time and parts of roofs would remain unpainted because of openings such as heating and cooling vents.

Keith Oleson

Keith Oleson. (©UCAR, photo by David Hosansky.)

In addition, white roofs would have the effect of cooling temperatures within buildings. As a result, depending on the local climate, the amount of energy used for space heating and air conditioning could change, which could affect both outside air temperatures and the consumption of fossil fuels such as oil and coal that are associated with global warming. Depending on whether air conditioning or heating is affected more, this could either magnify or partially offset the impact of the roofs.

“It’s not as simple as just painting roofs white and cooling off a city,” Oleson says.

More cooling for certain cities

The research indicated that some cities would benefit more than others from white roofs, depending on such factors as:

  • Roof density. Cities where roofs make up more of the urban surface area would cool more.
  • Construction. Roofs that allow large amounts of heat from the Sun to penetrate the interior of a building (as can happen with metal roofs and little insulation) are less effective in cooling outside temperatures when painted white.
  • Location. White roofs tend to have a larger impact in relatively warm climates that receive strong, year-round sunlight.

While the model did not have enough detail to capture individual cities, it did show the change in temperatures in larger metropolitan regions. The New York area, for example, would cool in summer afternoons by almost 2 degrees Fahrenheit.

A new technique

The study team used a new computer model, developed by Oleson and colleagues, that is designed to assess the impacts of a changing climate on urban populations and explore options for countering rising temperatures. This urban canyon model simulates temperature changes in city landscapes, capturing such factors as the influence of roofs, walls, streets, and green spaces on local temperatures. Oleson has successfully linked it to a computer simulation of worldwide climate, the NCAR-based Community Climate System Model, thereby enabling researchers to study the interactions between global climate change and urban areas.

The new model does not yet have the power to replicate the architecture and design of specific cities. Instead, the research team created abstractions of cities in the model, using classes of population density, urban design, and building construction. Oleson and his colleagues plan to continue refining the model to provide more information for policymakers concerned about protecting urban populations from the risks associated with heat waves and other changes in climate.

“It’s critical to understand how climate change will affect vulnerable urban areas, which are home to most of the world’s population,” says NCAR scientist Gordon Bonan, a co-author of the study.

About the article


The Effects of White Roofs on Urban Temperature in a Global Climate Model


Keith Olson, Gordon Bonan, Johannes Feddema


Geophysical Research Letters


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Save the paint, the snow we are getting is turning the roofs white for free.

Al Gore's Holy Ghost

It will help global warming by reducing temperature by 0.0005C over a century whereas natural cooling cycles will do much more, as well as bring misery as cold always does.

Richard deSousa

Being a former construction inspector I can tell you working on white roofs is difficult for the eyes. It’s like walking in a snowfield and the effect is blinding and extremely hot as the sun and roof reflection can make life miserable.


Okay…I’ll state the obvious….what is a NOAA weather station doing on top of a black tar roof. And they wonder what is causing the global warming.

Dodgy Geezer

It could probably be very helpful and cost-effective. So it probably will not be done.
I am reminded of Civil Defence studies in the UK during the 1950s. If a nuclear bomb were to airburst directly over a point there isn’t much you can do for the people beneath. But many miles out the flash can set fire to combustible objects like curtains and furniture. Brick houses and tiles, as are common in the UK are quite resistant to this, but the windows will let the light and heat in.
Running studies and simulations (not computer – real!) it was discovered that the most practical and cost-effective civil defence action was to paint your windows white. Most Britons have an old pot of white paint in their sheds, so it would be effectively free, and this would save many thousands of deaths in house fires around the periphery of a nuclear attack. So that advice was put in 1950s civil defence pamphlets.
CND joyfully made a major attack on the ‘stupidity’ of defending yourself against nuclear attack with a pot of white paint, and set the pamphlets up as a national joke. If I recall aright, they were withdrawn and never released.
I was very young at the time, but wondered why people should actively reject advice which made a lot of sense to me. I was obviously too young to understand politics…


What is wrong with these people they keep reinventing the wheel. It is well known fact that white or light coloured roofs prevent heat gain in buildings. Fine when its hot the building uses less air conditioning however in the winter the reflection of the heat will require more central heating.


Sorry the point is already made. I should have read more carefully.

Charles Barnard

Have a look at pictures of Bermuda, most of our roofs are made of stone, we keep the roof’s clean and white washed as they are used to collect rainwater to store in tanks under our houses. The 12,000 gallon tank under our house is considered small!

p.g.sharrow "PG"

“Man made Warming” ???????????????????????????????????/


This is so sad. There are certain aspects of the natural world which cannot be readily measuded so we attempt to produce mathematical models to explore them hypothetically. However this would have to be one of the easiest things to set up and experiment to test but they haven’t yet gatherd ANY data. Must really like the inside of thier offices.


Better “Hot tin roofs” (without the cat of “A cat on a hot tine roof”), they reflect more sun rays.
Seriously, these global warming scientists have their heads too warm, they need high albedo hats.


Now i understand climate science. It’s a sequel of Monthy Python’s flying circus. Our computer model shows that it could help. But we gotta do some more research to see whether it’s feasible. It’s not as simple as painting the roofs white. No, sure not, otherwise you wouldn’t need that honkin big computer, would ya? Oh, and you gotta do even more complicated models? My, my. Ministry Of Silly Walks.

John Luft

And what would the cost be? And how much CO2 would be produced in the manufacture and distribution of the paint? And how do you paint over asphalt and gravel roofs, etc., etc.?
What is obvious is that there is far too much money going to research and these guys are just looking for ways to spend it. Time to cut back on research money and let the scientists fight it out by prioritizing their research.


Here’s what Lord Monckton thought about Steven Chu’s idea last June.

James Sexton

Sigh, will their drivel never cease? They used a computer model to come up with “white paint will have a cooling effect”?? Really? Wow!!! One has to wonder what they’ll come up with tomorrow. Maybe something along the lines of “Computer models show that it is typically cooler at night than during the day!!!!”

Don Shaw

It seems as though these folks are obsessed with cooling which only applies in some climates. Do they have a clue as to how much heating energy (fossil fuels) is saved during the winter in other climates when the sun beating on the structure reduces the load on the heating system?
I agree that this may be effective in warm climates, but how about the rest of the planet. I realize the model is not so simple since the roof emmits energy to the atmosphere during the night that varies according to the color and texture of the roof.
I have the best of both worlds with my house since it is virtually surrounded by trees. In the summer, the trees keep the house cool, in the winter the leaves are gone and the sun heats the house.
Of course by studying this there is an admission that CO2 is not the only important factor. If this would get them off our back, I love the idea.
Of course it is stupid to collect temperature data on a hot black roof anytime of the year.


Does this mean that blondes are cooler than brunettes?
At the end of WW2 my father had the job of painting coal with whitewash. Really! There was a logical reason – nothing to do with keeping it cool.
See if you can guess what it was.
Reply: Preventing the spread of coal dust? ~ ctm


So it would be a Mirror’s Edge kind of world. I hope they paint some bits red so you know where you can duck/tumble/leap as you avoid the Green Police…

Dave Wendt

I thought the prevailing mantra from these guys was that UHI has never amounted to much.

David Gay

What will help the most, painting the roof white or covering the roof with 15 watt solar panels?

It is refreshing to learn tha UHI still exists; and, that its magnitude is still significant. Who knew!


Reflective metal surfaces are much better, both at keeping buildings cool (which is why they are very popular in Australia) and reflecting the sunlight back out to the upper atmosphere and space.

Peter of Sydney

Next, they will be painting the deserts white. How childish. haven’t they figure it out yet? Clouds are a much better alternative.


summer white paint to cool the building by reflection, winter in black paint to warm the house, help paint industry, provide more jobs, win win situation !
If steve chu is serious about the roof color, he just provided the half solution 🙂

Person of Choler

To work, this requires a paint that (1) has low emissivity (2) is resistant to weathering and (3) can withstand the frequent cleaning necessary to maintain that low emissivity.
Does NCAR recommend a coating to use?

Person of Choler

Rats! I meant HIGH emissivity. Low ABSORBTIVITY.
This is my idiot day.

Myron Mesecke

At least they actually admit UHI. But how much energy would it take to make the paint and apply it and how much pollution would be produced? I guess it would create some of those so called green jobs we keep hearing about.

Person of Choler

OK. REFLECTIVITY. I’m going home.

Climate Science:
(1) Make a graph.
(2) Connect the end points.
(3) Is it very flat? Yes -> Go to (1)
(4) The line is not too flat. Extend the line for 200 years.
It goes way up or down, yes?
(5) Publish.
(6) News Release: Computer model predicts disaster within 200 years.
(7) Threaten to smear businesses unless they show enlightened, unbiased support for your continued research.
(8) Collect grant money for further studies.
(9) Found a non-profit research institute for the good of mankind.
(10) Pay yourself $150,000+ out of the non-profits.
(11) Smile -> Go to (1)

Britannic no-see-um

Need to balance the ‘benefits’, (debatable), against the additional drain on the rather limited known economic reserves of titanium dioxide (~130 yrs at current consumption?).

Myrddin Wyn

You can also increase cooling by increasing the surface area.
Billions of tetrahedrons, p’raps made from recycled car tyre rubber and painted white, dropped on onto roofs by helicopters.
Science, it’s not difficult.


Sorry to to OT. I just spent some time browsing Obama’s new climate site. If you don’t mind feeling extremely nauseous, take a look at it at http://www.climate.gov
“WASHINGTON — US President Barack Obama’s administration announced plans Monday for a new office handling climate change, aiming to help businesses chart future plans as the nation shifts to a greener economy.
The first practical effect was the creation of a website, http://www.climate.gov, which came online Monday and brings together government resources on climate change for business, scholars and the general public.”

P. Hager

In 1987, the company I worked for had a new roof put on. It had a “Hi Tec” rubber membrane in addition to the traditional tar. The final step was to apply a WHITE urethane foam coating to reduce heat absorption.
There is nothing new under the Sun it seems.


I can see the point if it saves on aircon bills, but not if it increases heating bills.
But, the paper does not address this obvious question, as it is too diffuse and altogether at the wrong scale to be of any worth. If this computer modelling exercise was funded by the public, I’d say they have a case for a refund. Nothing personal you understand; it is just a quality thing.

carrot eater

“I find it humorous thatUCAR had to resort to modeling to prove something that can be measured empirically. ”
Without at least a little bit of modeling, would you have any idea how much effect it would have on a city? At some point, one has to do a few calculations.

Modeling with real world data after you’ve measured the effects on a few urban roofs would be the logical progression of events. There’s no mention of measurement of any kind. Measurement trumps modeling when seeking before and after effects. -A


1) “at least in theory, ”
If my aunt had testicles, she’d be my uncle … at least in theory.
2)“It remains to be seen if it’s actually feasible for cities to paint their roofs white, but the idea certainly warrants further investigation.
Translation A: Give me more grant money.
Translation B: I am retiring in 4 years. I may be able to carry this project through until 2014 after which I won’t care.
Clive the Canuck Cynic

Chris H

And city roofs constitute what proportion of a city’s surface area?…………
And what proportion of the earth’s surface?……………..

G. Arnold

I am a roof consultant and the subject of white roofs has been studied extensively for a number of years. California enacted Title 24 which requires new roofs have a surface with minimum reflectance and emittance values. Columbia University wrote an excellent paper for New York City on the subject. They calculated the cost of various actions including white roofs, more trees, vegetated roofs, etc. The paper is called Mitigating New York City’s Heat Island with Urban Forestry, Living Roofs, and Light Surfaces.
Chicago tried to enact a law requiring white roofs, but they’ve had problems. Oak Ridge National Laboratory wrote a computer program that calculates energy savings under different scenarios. In northern cities like Chicago, the dark roof surfaces actually save money because of the heat gain during winter months.


I guess the AGW gurus have ‘put their money where their mouths are’ and invested in white paint companies or white pigment futures…
(this can be the only logical explanation!)
OT: back in the glory days of 2007 Gore and Pachauri were best of friends – but they had a past, see:

Off Topic: Guardian still letting its guard down – well just a little…
Here anonymous IPCC wkg gp 1 writers complain about the invasion of social sciences method (of wkg gp 11) into their domain of hard science. And then we get this nice assessment of the situation:

“This is a transient and manufactured crisis and will likely go away with time,” one IPCC author said. “What the science community needs is a few huge donors to throw millions of dollars behind PR campaigns to counter the propaganda out there. We are being attacked through baseless smear campaigns and we are not PR experts.”

Steve Goddard

Boulder is cold most of the year. NCAR might save energy by painting their roofs a dark color.


“RJ (13:58:28) :
Sorry to to OT. I just spent some time browsing Obama’s new climate site. If you don’t mind feeling extremely nauseous, take a look at it at http://www.climate.gov

Love it. Now all we have to do is find mistakes and ridicule them.

Don’t know if anyone mentioned or asked this question, but the roofs of buildings is not the only part of the building warmed by the sun, is it?
What if the entire building was painted white? How about the parking lots, sidewalks, and streets?
Oh, and all vehicles should be white, too.
And, people should all wear white clothes.
And all the signs should be white.
And …


I recommend a trip to e.g. Spain, or Greece.
They must have had some excellent ancient supercomputer there that with the help of new (old?), sophisticated, state-of-the-art modelling taught them to paint their houses white.

A few groups are actually working on roofing materials that change from light to dark depending on the temperature, so it is more reflective in summer and less reflective in winter.


Right below that paper on UCAR they disclose an amazing new technique designed to replace Anthony Watts and Steve McIntyre.
Your tax money at work!

Nigel S

KeithGuy (13:43:13)
Painting coal…
No need for a reason, standard Army rules before an inspection. If it moves oil it, if it doesn’t paint it.
Also no signs of safety precautions for the people up on that white roof. Looks like a power cord dragged up the side of the building, tied round the vent and laid across the roof as a trip hazard. We try not to let the ‘elfin safety’ types bully us over here but they might have a point with that one.

I’m so sick of money being wasted in climate science. If this was publicly funded, then I hope you are all disgusted by this egregious waste of tax dollars.
Look at Michael Mann. Prior to his hockey stick, we all knew the Medieval Warm Period and Little Ice Age existed. We have a mountain of evidence across a dozen disciplines of science. But Mann had to “contain” it and get rid of it. In 1998 he published and apparently he believed that temperatures cooled for thousands of years and then shot up drastically. It took him until 2009 to “discover” the MWP.
That is 11 years of time and millions and millions in tax dollars wasted on “discovering” something we already knew!
Combine this with our current regime, err, government’s spending habits – ie, Pelosi spending hundreds of thousands on alcohol and food for entertainment – and it all starts to make sense. The government wastes our money, so they want these fraudster scientists to publish papers that make global warming look like a real threat. They can then use this fake data to get cap and trade passed which allows them to tax us more.
So they are wasting our tax dollars to do science that lets them tax us more.


“berniel (14:10:54) :
“This is a transient and manufactured crisis and will likely go away with time,” one IPCC author said. “What the science community needs is a few huge donors to throw millions of dollars behind PR campaigns to counter the propaganda out there.”
Yeah that’ll help. Look at the BBC science/enviro page today. They went into propaganda overdrive. 4 or 5 climate change articles up.

“Now i understand climate science. It’s a sequel of Monthy Python’s flying circus”
Dirk – we think alike. Have a look at the Village Idiot sketch.

Watch for the absolutely priceless lines at around 2:40
“Mr Figgis is no ordinary idiot, he is a lecturer in idiocy at the University of East Anglia”
They actually bestow mud on the new graduates!