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
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.
“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.
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
Title:
The Effects of White Roofs on Urban Temperature in a Global Climate Model
Authors:
Keith Olson, Gordon Bonan, Johannes Feddema
Publication:
I’ve see that mirrors are even better at reflecting light.
Jack Hughes (14:44:59) :
“Can’t we just wear tin-foil hats again ?”
I took mine off three years ago, and look at what’s happened! I’m with you.
“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.”
How does this square with the various adjustments made for UHI in surface temperature measurements?
KeithGuy (13:43:13)
Painting coal…
The answer.
You paint it to make sure that no one nick’s it. If you paint it white, and it is disturbed then there is this huge black hole, visible to all.
They you check all the local coal holes for someone with white paint on their coal. then it is time for the plod.
Charles Barnard (13:32:48) : collect rainwater to store in tanks
Thief! That sort of anti-social eco-corrupting behavior can get you thrown in the dungeon in some of our states in the USA. Washington, Colorado, and Utah are examples. There may be others.
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On topic: On multi-story buildings the overall effect internally will be small and as roof tops are of little extent on Earth the world wide increase in albedo will be small. In most cities the area covered by streets and parking lots is large but the same issue as above applies. Regardless, this scheme, if paint is used, will have undesired side effects. Solar collecting paint or panels may find some use.
My own suggestion is to spray the roof tops with ocean water and as the water evaporates it will take up energy and cool the surroundings. The collected minerals could be processed and used, especially the salt as it will be needed to clear the streets and highways of ice as the climate cools.
Ocean Water and Its Wonderful Potential
http://www.terrapub.co.jp/e-library/dow/pdf/chap2.pdf
I seem to recall the Obamastration talk earlier about forcing white roofs.
I doubt that they considered what that would do to snow loads and retarded melting time on our high altitude Colorado homes.
Reversible panels? A bit labour-intensive but might do the trick.
jorgekafkazar (15:23:26) : wrote
Stacey (13:32:00) : “Sorry the point is already made. I should have read more carefully.”
The point was easily missed, since they seem to be underplaying the problem of lower solar heating in winter. I was looking for that specifically, and it still took a while to find.
I studied this sort of thing about 50 years ago. You need a coating that is white in summer and black in winter. Any ideas?
Brown roofs.
The full article “The Effects of White Roofs on Urban Temperature in a Global Climate Model” is behind a paywall.
The scientists involved are tooting their own horn in public, but are publishing in semi-private. So, I would have to pay to check if they have published their data, methods, and computer models. I don’t trust scientists who tout their results and claims, before a second and third group has given the paper a scientific review and it has been open to criticism for quite a while.
Peer Review is not Scientific Review. Published suggestions and claims are common, and usually wrong, inconsequential, or impractical. Or all three.
This proposition (without the reference to UHI effects — pertaining only to emissions) was the subject of a hilarious piece in the Winnipeg Free Press some time ago. My reply, at the top of the comments was mainly a link to some very well-formed rebuttals of the idea, my favourite being to member of an industrial company in whose economic interest it would have been to promote the roof-painting business, who points out that in a cool climate like Winnipeg’s, the proposition is nonsense, and would likely lead to greater emissions, not less. He said that this must be considered on a city-by-city basis as there are a number of factors to consider and the result is not at all clear. Any bets that this computer model neglects to take a majority of the relevant factors into account?
In hot climates, cooling the city makes sense, but in cool climates, killing the UHI effect will simply increase the winter heating bill for everyone, and increase consumption of energy resources. UHI is not always a bad thing. One-size-fits-all solutions are sure to be the wrong solution some of the time.
In any case if you just paint roofs and parking lots white around all Stevenson Screens in the world, we would see within a couple of years a sudden, pronounced, statistically significant cooling of the globe. But it would be as meaningless as the current data set that indicates warming, and for the essentially the same reasons.
In the late 19th century the only rust preventative paint available was red lead, in South Africa this was widely used and the heat absorbtion made an alternative essential. The paint didn’t change, the Boers found the solution. It was a double roof.
The house was given a roof as normal but a foot or so above that roof another roof was built. The eaves were sealed off to prevent the ingress of wild-life but wire-protected apertures were left to allow the air through. At the apex of the roof stood a louvered and roofed tower. When the air between the roofs heated it rose, and escaped via the vent on the top of the building. Cool air was drawn in from the verandah which surrounds all of the houses of that era.
Result? The house stayed cool.
White paint? Wrong choice.
Hey! I’ve got it! Use a fleet of crop dusters to paint the entire city white! That’ll save lots of time. Dang, time to write to AlGore!
jorgekafkazar said: I studied this sort of thing about 50 years ago. You need a coating that is white in summer and black in winter. Any ideas?
Thermochromic paint.
“I studied this sort of thing about 50 years ago. You need a coating that is white in summer and black in winter. Any ideas?”
Sounds like the perfect “shovel ready” green job program. During the spring, people dressed in white painters uniforms will be painting your roof white, then in fall people in black painters uniforms will be painting your roof black. Just hope they don’t run afoul of the “Green Police”.
kwik (15:13:53) : the gray-scale based on lattitude
I will suggest the cosine function. Send my consulting fee to . . .
I would like to thank the SUN for doing a great job for me over the past 3 years.
“Over longer periods of decades to centuries, solar activity waxes and wanes with a complex rhythm that researchers are still sorting out. The most famous “beat” is the 11-year sunspot cycle, described in many texts as a regular, clockwork process. In fact, it seems to have a mind of its own.
“It’s not even 11 years,” says Guhathakurtha. “The cycle ranges in length from 9 to 12 years. Some cycles are intense, with many sunspots and solar flares; others are mild, with relatively little solar activity. In the 17th century, during a period called the ‘Maunder Minimum,’ the cycle appeared to stop altogether for about 70 years and no one knows why.”
Solar Dynamics Observatory Set For Feb 9 Launch
http://www.redorbit.com/news/space/1819249/solar_dynamics_observatory_set_for_feb_9_launch/
There is no need to go so far back in time, however, to find an example of the cycle’s unpredictability. Right now the sun is climbing out of a century-class solar minimum that almost no one anticipated.”
NOAA only wants to patch a faulty system by diverting to roof colour. On one hand they deny the UHI but say that cities have an impact on global warming. Sure it is hotter during day time but it’s only a heat capacitor that delays the discharge. It only delays the heat release but does not contribute to it. Also, as we said last week, the UHI is insignificant compared tot the rest of the land, water and snow/ice covered area.
What? the city folks feel it’s too hot during night time? That’s what happens when you live in a chicken house, stacked on each other.
I have a (nearly) white tin roof. I also have a weather station mounted 2 metres above the roof. I have another temperature monitoring point under the roof at the side of the house, which is next to a brick wall and above concrete.
The one on top of the roof routinely measures 1-2 degrees cooler than the one in the shade. True story.
I know somoene with a black tile roof. Their house is unbearably hot in summer.
New Federal Climate Change Agency: http://abcnews.go.com/Technology/wireStory?id=9777038
They never learn …. I suppose they had built the billions from a carbon tax into their plans, and just can’t let go ….
Why put a temperature measuring station in direct sunlight? No one who works outdoors, such as farmers, construction workers, you name it, would ask for a temperature reading in direct sunlight. In fact, they would consider you insane for giving a temperature reading from direct sunlight. Yes, I know the thermometer is in that little box. But that little box will heat up like the dickens. Well, that’s what you get when you leave temperature measurement to eggheads.
The World needs an entirely new regime of temperature measurement created from scratch.
John Luft (13:36:43) :
…….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.
This could not be more true. I’ve been listening to a radio ad for the last year, which plays several times each day. I was out very late one eve, and heard it at 2 am, admonishing citizens to plan for disasters. It is a government service announcement…. playing in the wee hours of the morning….. stimulating the economy….. because we’ve printed a trillion bucks and can’t think of enough ways to blow that much cash.
I read Monktons justafiably sarcastic destruction of Chu, I notice an error (please correct me if I am wrong), in working out the surface area his maths assumed it to be flat (oh the irony), I do not know what conversion factor to apply in making a flat surface into the area swept by the suns rays but I would think that we can start by halving it as half is in the dark, then as we are discussing a sphere only the equator gets 100% one pole will get 0% so we can divide again, perhaps by 2/3 this time so we have to divide 0.2 F by half and by 2/3 my abacus gives me about 0.07F The really frightening thing is this was one of the saner ideas.
John F. Hultquist (15:36:08) :
Charles Barnard (13:32:48) : collect rainwater to store in tanks
Thief! That sort of anti-social eco-corrupting behavior can get you thrown in the dungeon in some of our states in the USA. Washington, Colorado, and Utah are examples. There may be others.
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Reply:
No cause for alarm; he’s just sequestering H2O, which is undoubtedly a much more effective GHG than CO2. He should get a medal, except for the fact that 70% of the earth’s surface is contributing that nasty H2O into the atmosphere. That rather overwhelms his efforts at being “green”.
So drink more H2O, particularly that laced with CO2. But don’t you dare belch or pee.
Why does UCAR get UHI mixed up with climate change? Assessment of climate change would have the UHI of city sites eliminated. They seem to think that UHI causes climate change – it does when it is left in the data and not properly adjusted DOWNWARD.
The U. S. Navy has been doing this for decades (probably measured in fractional centuries). In the tropics, ships that are moored in port for extended periods, put up white canvas awnings to keep the tropical sun off the decks and bulk heads. With out the sun shade the metal superstructure gets so hot it will burn you during the heat of the day. They take the awnings down when they go to sea and there is air motion to cool things off.
Radical concept — shade, and a reflective shade at that — just like the pull down window shades my grandmother used 50 years ago to keep the house cool during the summer. White washed buildings are also common in the Mediterranean, I wonder how the ancients did their computer model studies to come up with that idea to keep the buildings cool?
These guys need to get out in the real world more, read a bit of history, and go find a sidewalk cafe and drink a beer and marvel at how cool it is under the collapsible umbrellas.
The U.S. Navy also uses roof construction with double roofs in the tropics as described above in South Africa.
Larry
I live in an area where snow usually remains on the majority of rooftops all winter long. Interestingly, I still see UHI every day I go into town. Of course, it may be a bit less … or not.