Painting The World's Roofs White Could Slow Climate Change

Hugh Pickens writes "Dr. Steven Chu, the Nobel prize-winning physicist appointed by President Obama as Energy Secretary, wants to paint the world white. Chu said at the opening of the St James's Palace Nobel Laureate Symposium that by lightening paved surfaces and roofs to the color of cement, it would be possible to cut carbon emissions by as much as taking all the world's cars off the roads for 11 years. Pale surfaces reflect up to 80 percent of the sunlight that falls on them, compared with about 20 percent for dark ones, which is why roofs and walls in hot countries are often whitewashed." (Continues, below.)

"An increase in pale surfaces would help to contain climate change both by reflecting more solar radiation into space and by reducing the amount of energy needed to keep buildings cool by air-conditioning. Since 2005 California has required all flat roofs on commercial buildings to be white and Georgia and Florida give incentives to owners who install white or light-colored roofs. Put another way, boosting how much urban rooftops reflect would be a one-time carbon-offset equivalent to preventing 44 billion tons of CO2 from entering the atmosphere. 'For the first time, we're equating the value of reflective roof surfaces and CO2 reduction,' says Dr. Hashem Akbari. 'This does not make the problem of global warming go away. But we can buy ourselves some time.'"

Pavement

[jasonhamilton]

Makes me wonder why roofs and not pavement. There's a lot of roads and parking lots around the world. Seems like there's more surface area of those than roofs.

Re:Pavement

[Chabo]

From TFS:

that by lightening paved surfaces and roofs to the color of cement

Personally, I wouldn't want to drive on a surface that bright; I'd be squinting even with my sunglasses on!

Also, as a current resident of California, I can see the value in having a light-colored car or house, but as a former resident of New Hampshire, I can tell you that having a black car and black roof on a cold but sunny winter's day is very helpful! Snow slides off my car roof with ease, and it means I didn't have to turn the heat up quite so much!

Re:Pavement

[Jah-Wren Ryel]

Personally, I wouldn't want to drive on a surface that bright; I'd be squinting even with my sunglasses on!

If you've driven on an interstate in the mid-west, chances are you've driven on cement. It really isn't any worse than asphalt.

Re:Pavement

[conteXXt]

Asphalt has it's issues in cold climates.

Up here in Toronto, highways are concrete (yes concrete) with an asphalt layer on top.

Every summer the asphalt has to be repaired, leading to our two seasons.

Winter, and Road Repair.

Things may be similar in the midwest but I am only speculating.

Re:Pavement

[Chabo]

In New England, we have four seasons:

Almost Winter, Winter, Still Winter, and Construction.

Re:Pavement

[pcolaman]

In Florida, we have only one season:

#RandomWeatherPattern

Re:Pavement

[changa]

In California we have 3 seasons: Spring, Rain and Fire.

Re:Pavement

[Sparky McGruff]

I think you've misnamed a couple seasons.

I believe the seasons are Allergy, Mudslide, and Fire.

Re:Pavement

[JWSmythe]

    That's a blatant lie. The weatherman was joking about it a few nights ago, but it's true.

    Season 1 - Hot: February 15 through December 15

    Highs from the high 80's to low triple digits.
    Lows in the mid 70's to high 80's.
    50% chance of afternoon and evening showers and thunderstorms.

    Season 2 - Cold: December 16 through February 14

    Highs in the mid 60's to low 80's,
    Lows from the high 20's to mid 70's.
    50% chance of afternoon and evening showers and thunderstorms.

    I've lived here for 30 years. That's always an accurate prediction. The only variation is when a tropical storm or hurricane blows through, and they only increase the chance of rain from 50% to 100%.

Re:Pavement

[hubert.lepicki]

We must have even worse climate here in Poland as they seem to be repairing roads for last 20 years with little success...

Re:Pavement

[ceoyoyo]

In Canada we have two seasons: winter and what they call winter in New England.

Re:Pavement

[MichaelSmith]

Here in Victoria, Australia 90% of road work happens in the last month of the financial year, which is now. I used to work for the state road authority. One year, on the last day of june:

• Boss: (pointing to a bit of gear) whats that?
• Me: An HP pen plotter
• Boss: How much did it cost?
• Me: Seven thousand dollars
• Boss: Buy another one. today

Re:Pavement

[iroll]

Same here in Arizona; freeways are built from concrete, and then a layer of rubberized asphalt is paved over it. Until a few years ago, most of the freeways were bare concrete; IIRC one of the major reasons for the asphalt was to reduce traffic noise.

Re:Pavement

[Hognoxious]

two seasons. Winter, and Road Repair. Things may be similar in the midwest but I am only speculating.

The only part of the midwest I can speak for is southern Michigan (in particular the I75 to Rhubarb Custard airport) and you are totally wrong.

They don't repair the roads there ever.

Re:

[vonart]

Living in Western Mass, I assure you that they never pave asphault "in a day". We have areas they've been working on for months... and down in CT, one highway that was undergoing repaving was that way for well over a year. Lane closures and so on.

Re:Pavement

[lorax]

If all you are doing is laying down asphalt maybe it will go that quickly. After you have a few layers on a main road it takes longer because

1) you can't shut the road down completely
2) you can only work at night
3) you have to mill off the old layers first
4) you have to clean off the pavement right before laying asphalt
5) you have to put some sort of black goo down so the new asphalt sticks to the old
6) Whoever is doing the contracting seems to wait for random amounts of time between stages.
7) you do it in 5 mile chunks.

Near where I live there is a major interstate and it can take a month to re-pave, driving over the grooved pavement makes a lot of noise and the transitions from the grooved to old asphalt mean your car goes up a couple of inches.

I suspect 6 and 7 have more to do with bureaucracy/lowest bidder/political considerations than to technical reasons.

Re:

[Anonymous Coward]

Ok, I'll toss a chunk of cement at your eye and a chunk of asphalt at the other eye and you tell me which is REALLY easier on your eyes..

Re:Pavement

[sexconker]

Then I'll dab your eye with wet cement and then dab your other eye with molten asphalt and you tell me which is REALLY easier ON your eyes.

Re:Pavement

[tsalmark]

I love all these Concrete examples.

Re:Pavement

[danbert8]

Not just quick dry... All cement is an exothermic reaction. And would people SERIOUSLY stop calling concrete cement. Roads are made of concrete, which is a mixture of cement, aggregate, and water. Cement is only the binder of the mix.

Re:Lisa.

[ZackSchil]

How could I ever forget good old Lias?

Re:Pavement

[GrayCalx]

I'd like to introduce you to my unmarried sister Maude.

Re:

[tiedyejeremy]

Does she have... uh... big uh... eyes? ;)

Re:Pavement

[JWSmythe]

    It's a little of this, or a little of that.

    I've noticed, new asphalt in the Florida summer (say 90F to 110F) roads turn into mirages, Entire cars can disappear in the at less than 1/10 mile. You can see the heat rising from them.

    In older asphalt roads, where they're sun bleached and worn, the heat isn't as much of a problem.

    And I've never seen it on concrete roads.

    I've wondered about roads and roofs being a contributing factor to global warming. There's a lot of square miles of roofs and roads that have increased relation to the population. It's always been notable that cities are hotter than the countryside surrounding them.

    I've wondered about the heat put off by internal combustion engines. We're taking massive amounts of stored energy (oils, etc) and turning them into heat and motion. How many BTU per hour does an average car put off? In passenger vehicles, even in the winter, a small fraction of that heat is redirected into the passenger compartment, and can turn it into a freakin' oven. Look at the size of the heater core versus the radiator.

  In the summer, that's increased, as the load on the cooling system is added onto by running the A/C in the car (more load on the engine). The amount of heat moved from the passenger compartment to the outside should be a wash, as should the heat transfer from a building.

Re:

[geekprime]

And far LESS expensive in the long term.

Re:Pavement

[CanadaIsCold]

There is a tipping point to the cement argument which is why you don't see it in truly cold locations like Canada. Cement roads have a longer lifespan than asphalt and it works out to be cheaper in some locations. In other locations ,due frost, the ground moves too much to see the return on investment. In Canada where there is heavy frost every winter a cement road would still be required to be repaired every year but at a much greater cost due to the cracks caused by frost. This is why you see more cement roads in the southern states and less in the northern. Asphalt's lower cost to install and repair makes it a better fit in colder areas. Neither is a perfect solution but each serves it's purpose in it's place. The perfect solution, as always, is to give us our flying cars.

Re:Pavement

[KillerBob]

Ontario Highway 115, which runs between Peterborough, Ontario, and Hwy 401 just outside Toronto, is a test road. They put it in decades ago, and tested several different road surfaces, including several different types of cement and light-coloured road surfaces.

The cement has, on the whole, stood up better than the asphalt. And believe me, it gets cold in Pete.

Autobahn is cement? I don't think so

[heinzkunz]

I drive on the Autobahn every other day, and practically all of it is paved with asphalt.

Also, mean temperatures in Germany (13C) are much higher than in Canada (-8C).

If you want proof, take a look [almostsmart.com]:
1) It's asphalt.
2) The beer is not frozen.

Re:Autobahn is cement? I don't think so

[Froggie]

Europe is more densely populated, and concrete roads just don't stand up to the traffic levels. The old Newark bypass on the A1 and the originally-concrete M11 in the UK are testament to that.

Re:Pavement

[CheeseTroll]

They can scrape & repave large sections of a highway in a weekend if using asphalt, compared to weeks for cement. Of course, if they're doing cement it usually means they're tearing up the whole road and rebuilding it from the bottom up. Also, when the top layer of cement wears out, they often throw a layer of asphalt over it to extend the road's life a few more years.

Re:Pavement

[Avin22]

Although this would reduce the amount of energy used for cooling, heating costs would go up. For most people, it takes far more energy to heat a house than cool it. It takes 1200 KWh to cool a house in a temperate climate for a year, but it takes 12000 KWh to heat one . It is more useful to look for ways to heat a house more efficiently than cool it.

Re:Pavement

[MarcoAtWork]

uhh, in the winter your roof is covered by snow anyways, so the color your roof is not going to make any difference. And for states/countries where it doesn't snow in the winter, you probably also don't need 12000KWh to heat them up.

Huh? what are you talking about?

[ClioCJS]

There's snow on my roof perhaps 2 weeks tops during the winter. But I have to run my heat for over 6 months of the year. I topped 5000kwh on a 2500 sq ft house at a cost of $450 this december. Nice try, but...

Re:

[SatanicPuppy]

It depends on where you live. Completely.

First off, your home insulation should be good enough that you'd only see a modest benefit from the solar heating. Second, living that far north (above say, pennsylvania (39 degrees north/south for you furriners)) and the amount of daylight you get is pretty low in the winter anyway.

I live in the South, and I run the AC between 6 and 8 months of the year, and, thanks to a big tornado earlier this year, I heated my house for most of our short winter using free firewoo

Re:Pavement

[syphax]

In the winter, a dark, hot roof doesn't heat a house very effectively (heat rising and all that- plus there's less incident solar energy).

In the summer, there's a lots of solar energy hitting your roof; and a hot roof leads to a hot attic, which retards flow of heat/hot air in the house (heat rising and all that).

So, a light-colored roof has a much more profound impact on cooling than on heating.

A metal roof will help both heating and cooling- and snow slides off them- but they are not cheap!

Re:Pavement

[jandrese]

What do you mean they're not cheap? The corrugated steel roof has been the roof of choice for people who can't afford tarpaper for ages.

Re:Pavement

[drinkypoo]

The other replies have told you why you are wrong. I will tell you how to harness the principle to your benefit, but it has nothing to do with your roof. I saw it in Mother Earth News (how apparently ironic that the acronym is MEN) but the idea is old; you paint the exterior wall black, cover it with a sheet of glass or plastic, and put a vent at the top and bottom. In the summer you would prefer to cover it with white shutters to reflect unwanted solar energy. In winter, you open the shutters and the vents. Convection provides circulation.

In theory, you could do the same thing on your roof, but you'd need some sort of forced air system to bring the air down where you can use it; all you need in your home is a ceiling fan.

Re:Pavement

[Stevecrox]

A house built to with heat conservation in mind should almost heat itself. I've moved into a new flat building in the UK, between all the insulation and double glazing its actually hard for me to get the flat cooler than 21 degrees.

During the winter when it reached -8 degrees outside, my flat without any heating was at 16 degrees. My neighbours have the same issue, we only have the one small flat below us so the heat isn't coming from downstairs.

I can think of several other new buildings which suffer from this problem. If your going to argue about the color of a building mandating improved heat conservation should remove most of the heating costs.

Re:Pavement

[Dare nMc]

In physics, a black body is a perfect absorber of light, but by a rule derived by Einstein it is also, when heated, the best emitter. [wikipedia.org]
so if your house/car/etc is heated, then yes it emits more heat from the body if black. Thus it is a worse insulator and (as you observed) heats the snow on the outside of your car faster. So yes if your goal is to heat the outside of your car in winter, black is best. If keeping the stuff on the inside warmer than the outside, is your goal, it may not be best in black (definitely not assuming a lack of radiated light, like at night.)

Re:Pavement

[Dutchy Wutchy]

If the roads are painted white with the standard white road paint, the coefficient of friction will be reduced (much more so when wet).

Also, where is all this paint coming from? What are the environmental and economic impacts of making all of this paint?

Re:Pavement

[oldhack]

We'll squeeze the white color out of white baby seal's fur, top that off with the white pigments from dirty hippies' soy milk stash.

Re:Pavement

[cdub1900]

Believe it or not, there is a lot of research going into creating lighter colored surfaces for roads. One of the advantages is that it takes less light (and thus energy) to light up the surface at night. This also decreases the amount of "light pollution" you would have around town. There are other advantages to improving water quality and decreasing noise.

http://www.eoearth.org/article/Cool_paving [eoearth.org]

However, one of the current hangups is how to keep them light? Unless we can also change the rubber in the tires to be lighter color as well, the road surfaces just end up black again in high traffic areas like California.

Re:

[Chabo]

Unless we can also change the rubber in the tires to be lighter color as well

A comeback for white-wall tires? Awesome!

Re:Pavement

[CarpetShark]

Makes me wonder why roofs and not pavement. There's a lot of roads and parking lots around the world. Seems like there's more surface area of those than roofs.

What you have to understand is that there's climate change, and the movement to save the environment. Then, there's "global warming" and the movement to sell you yet more products that can "save the environment!!" (despite the fact that selling unnecessary products and not living simply enough is the main cause of damage)

Re:

[Mike_K]

While others have pointed out that the article DOES talk about pavement, there is an additional reason to paint roofs before roads: roofs overheat our houses and we use more a/c to cool them off. Roads to not need cooling (though cars on them do, but that is a secondary effect).

m

Re:Pavement

[Altus]

not only that, the pain they use on roads is terrible for traction. Even just stop lines can be brutal for motorcycles.

You would have to add the pigment to the actual road material for it to be at all practical.

Re:Pavement

[flyingsquid]

Just use white minerals in the asphalt. Quartz and limestone, either as gravel-sized or sand-sized grains, would provide good traction and significantly increase the reflectiveness of the surface. Limestone does tend to dissolve in weak acids, but it's slow enough that it shouldn't decrease the lifespan of the road that much more than standard wear and tear, particularly in drier climates.

Re:Pavement

[hplus]

The idea has some merit, but Chu is yapping his face off about Global Warming in order to make sure his buddies get more dumptruckfulls of money to further "study" and "quantify" exactly how much this might help.

So the idea has merit, but anybody that tries to study it is just in it for the money?

Paint the bears, too

[snsh]

Let's also paint all the Grizzly bears white. That will address the problem of disappearing polar bears.

Re:Paint the bears, too

[InterGuru]

Let's also paint all the Grizzly bears white. That will address the problem of disappearing polar bears.

This will disturb the bears to the point that they become bipolar bears.

Bookwormhole.net [bookwormhole.net] -- over 11,000 published book reviews.

Moon

[SnarfQuest]

Everyone should hang their bare white bottoms out the window, in order to reverse the global warming trend.

Re:Moon

[tool462]

I don't know that it will be enough to counter the increased methane emissions...

and make all

[markringen]

and make all the birds blind. we had a man in the neighborhood who had a white roof and it was filled with dead birds. birds fly towards white objects for some reason as if it's the sky, and splatter to death.

Re:and make all

[oneirophrenos]

Or give all the birds laxatives...

Re:

[wonderboss]

I have two large buildings with white metal roofs. Birds don't fly into either of them.

Re:and make all

[whiledo]

They do not fly into them, either.

Re:and make all

[scubamage]

That's also why roofs are painted that way in tropical regions. No birds on the roof means you can gather a clean water supply from rainfall. Bermuda does this with excellent success.

Time out

[XanC]

Wasn't there a study a year or two ago, which was loudly trumpeted by NPR, CNN, MSNBC, etc, that concluded that manmade global warming (or "climate change") was already a sure thing, and it was way past too late for us to do anything about it now.

So, uh... What happened to that? Was that fake, or is this guy ignorant? Or do climate-change types believe stuff whenever it's convenient for them?

Re:Time out

[Tenek]

Maybe there's some legitimate debate over how reversible it is, independently of whether or not it's happening.

Re:Time out

[SnarfQuest]

Is it likely to be reversble if it isn't happening?

Re:Time out

[MrMista_B]

No, that was accurate - the climate is changing all the time, and humans have caused various changes to accelerate in ways that are detrimental to the survival of our species (growth of deserts, loss of farmland, etc.)

What this is proposing, is a way to mitigate some of the detrimental changes.

That aside, why the snark? I understand that people of course have personal investment in their enviroment (it's where we live, after all), but for someone proposing a simple change like this that could have multiple beneficial results for our species, I'm not sure why you feel so threatened.

Re:

[SnarfQuest]

Or do climate-change types believe stuff whenever it's convenient for them?

yes

Re:Time out

[stpere]

Well, even if we can't reverse the process, there are other good reasons to lower our energy consumption.

Energy isn't free; by polluting less, you often spend less in the long run... It's not only good for the planet, it's good for the economy in general.

Both shouldn't be seen as incompatible things.

Re:

[Mashiki]

Don't you know? The wind blows one way, than the other. We're doomed, then not doomed. Followed by we're so guilty we're already screwed that we should just wipe out humanity for the next apex species.

Yeah, seriously this stuff gets old pretty quick. Half the reason why you can't take stalk in most of it.

Re:

[pcolaman]

The fact that it was reported by NPR, CNN, and MSNBC tells me all I need to know about the likeliness of it being a legit claim. My only question is which analyst on which of those networks pulled the claim out of their ass and allow the other networks to co opt that info.

Re:

[An Onerous Coward]

Oh, and the whole thing with the world going through a cooling period now probably has something to do with it.

Great Cthulhu's corpse, do we have to go through this again?

Let's go over the chart [wikimedia.org]. 1998 (the big uppy spiky thing near the end of the graph) was a huge warm year, because of El Nino, not because of global warming per se. 2008 (the downy liney thing at the end of the graph) was an exceptionally cool year, because of La Nina, and not because of any long-term cooling trend.

Get rid of those two p

Comment removed

[account_deleted]

Comment removed based on user account deletion

Re:

[hankwang]

Unfortunately, producing the massive amounts of white paint needed to paint all these surfaces and maintain them produces about as much CO2 as was saved by starting this excellent project.

You need about 100 g of paint to cover a square meter. Suppose that the paint costs 1 kg worth of fuel to manufacture. The amount of sunlight it reflects over 10 years in a sunny climate is on the order of 50 gigajoules, or about 1000 kg of fuel to burn. Even if only 10% of the heat has to be cooled away by airconditioning

Re:

[pcolaman]

Who wants to bet he just invested in a roofing supply company?

White asphalt?

[idontgno]

Now, you smile, but he's done a calculation, and if you take all the buildings and make their roofs white and if you make the pavement more of a concrete type of colour rather than a black type of colour, and you do this uniformly . . . it's the equivalent of reducing the carbon emissions due to all the cars on the road for 11 years.

Now all we need is white tar...

Re:White tar?

[13bPower]

You can get that in Afghanistan.

Re:White asphalt?

[JSBiff]

There might be some safety issues with making road surfaces reflect more light. . .things that come to mind:

* Increased road glare on sunny days - good sun glasses could largely deal with this, but if you don't happen to have a pair of sunglasses, you might be having a pretty hard time seeing on very bright days.

* Night driving: harder to see the painted lines and reflectors embedded in the concrete (I'm not sure if this would really be much of a problem or not, but maybe could be)

* Winter driving - In the winter, I'm sure that black pavement absorbing sunlight has some beneficial effect in the form of melting ice off the road sooner than light-colored pavement would. Lighter colored road surfaces might lead to ice lasting longer, or requiring more salt to be put on the roads by road crews.

Other Pollution

[ironicsky]

I wonder if he calculated the amount of green house gas and other pollution would be created by manufacturing all this new paint. If they were you make roofing tiles and shingles white, what would the pollution cost from people throwing out their old roofs to bring in new white ones? Same with roads. My favorite roof solution, and something I plan on working on this summer or next summer is to turn my garage roof in to a natural garden by placing a protective tar paper over the shingles, a couple of inches of dirt and then grass or moss seeds. I'll let nature reclaim my man-made structure. Inch for inch, it would be just like grass growing on the ground, except not.

White roofs

[Geoffrey.landis]

Not really new: Knight science journalism tracker link [mit.edu], Christian Science Monitor Blog: [csmonitor.com]

and, the original source: Powerpoint presentation from LBL: "Global Cooling: Increasing World-wideUrban Albedos to Offset CO2," Hashem Akbari PDF file [mit.edu]

Double benefit

[EvilToiletPaper]

Whitewash also absorbs CO2 from the atmosphere and turns into Calcium carbonate to get that milky white look, so in addition to reflecting sunlight, we also remove some CO2 from the air. On the downside, whitewashed walls look butt ugly.

Anyone know what the environment/economic cost of making all that whitewash is?

Nice to have a Sec of Energy actually Read the Lit

[sampson7]

There are very free lunches in the world of energy production and consumption. Lightening the color of pavement and roofing materials about as close as we get. From a DOE study [osti.gov]:

As an example, computer simulations for Los Angeles, CA show that resurfacing about two-third of the pavements and rooftops with reflective surfaces and planting three trees per house can cool down LA by an average of 2-3K. This reduction in air temperature will reduce urban smog exposure in the LA basin by roughly the same amount as removing the basin entire onroad vehicle exhaust. Heat island mitigation is an effective air pollution control strategy, more than paying for itself in cooling energy cost savings. We estimate that the cooling energy savings in U.S. from cool surfaces and shade trees, when fully implemented, is about $5 billion per year (about $100 per air-conditioned house).

Amazing, isn't it? Two to three degrees in temperature reduction in a major city just by resurfacing, repainting, and planting trees. Yeah, sure, it's not sexy. But the cost savings ... staggering. Add in the health benefits of reducing smog, plus the reduction of human misery from over-heated citys, and you wonder why we haven't done this years ago.

I know this is going to sound like a self-serving political statement from a hardcore Democrat -- but well done, President Obama. You picked a scientist to run an agency. You gave him a mission to better humanity through reducing carbon emissions and energy consumption. You gave him a platform where he would be heard. Well done indeed.

Re:

[Jah-Wren Ryel]

well done, President Obama. You picked a scientist to run an agency. You gave him a mission to better humanity through reducing carbon emissions and energy consumption. You gave him a platform where he would be heard.

Heard, but will he be heeded?
Cynic says no.

Re:Nice to have a Sec of Energy actually Read the

[radtea]

I know this is going to sound like a self-serving political statement from a hardcore Democrat -- but well done, President Obama.

My cynicism knows no bounds, which gives me to think what the Democratic response to this might have been if a Bush Administration official had proposed it. I'm betting something to the tune of, "Oh those damned Republicans they want to use band-aid technological fixes so they can go on driving their SUVs over baby polar bears for another ten years!"

I think this is a good idea, and if Chu can make it happen (again, colour me cynical) it'll be a good thing, particularly because of the reduced energy demand aspect, which will help with the whole peak oil deal.

But I can't help thinking about how mindless partisans (not necessarily you) would have reacted if the Offence rather than the Defence had suggested this (both parties are ultimately on the same team, of course, representing the plutocrats united against the people.)

why roofs in hot countries are whitewashed

[Culture20]

That's nice for the hot countries. What about cold countries? Maybe we like having black roofs and roads to melt the snow faster if there's a little opening?

Re:why roofs in hot countries are whitewashed

[pz]

That's nice for the hot countries. What about cold countries? Maybe we like having black roofs and roads to melt the snow faster if there's a little opening?

Yes. Or nearly so. I just happened to be doing some research on roof treatments. There are basically two types -- for flat roofs. Angled roofs are a different story since they're angled for snow and rain shedding. The two types of flat-roof coatings are white paint and aluminum paint.

Here's the link: http://eetd.lbl.gov/coolroof/coating.htm [lbl.gov]

White paint coatings use titanium dioxide as a pigment (very, very white) and reflect 70-80 percent of incident light. That means they keep the roof cool in the summer. They are, however, reasonably transparent to IR from below, so unfortunately do nothing to hold heat in during the winter.

Aluminum paint coatings use little flakes of alumnimum and reflect about 50-60 percent of incident light. That means they also keep the roof cool in the summer. They are, however, much less transparent to IR from below, so help keep in heat during the winter by reflecting it back down.

Then again, nothing stops you from painting your flat roof white or aluminum and unrolling black sheeting during the winter to help absorb heat from the sun.

Re:

[Culture20]

How does that work? I would expect that the color of the roof would be irrelevant if it was buried under a blanket of white, insulating snow - no sunshine would hit it.

All you need is a little crack of black and you'll start melting. One of my favorite methods of asphalt-driveway shoveling when there's only 4-8 inches of snow: Drive out to the road, packing down some snow, then shovel two lines right next to the wheel-trenches. If the temperature is at least 20F, then the whole driveway melts and evaporates in one sunny afternoon. If it's 10-20F, then at least in a few days there is considerably less snow, but you'll have some ice (which is easy to scrape to the side)

According to Rush Limbaugh ...

[tiedyejeremy]

White paint CAUSES GLOBAL WARMING by reflecting light into the atmosphere! http://www.rushlimbaugh.com/home/daily/site_032609/content/01125110.guest.html [rushlimbaugh.com]

Re:According to Rush Limbaugh ...

[geekoid]

"I don't want to get too technical on this black paint versus white paint and reflection of heat and so forth because it misses the point."
He always says something like that and what it really means is "I don't want to get too technical on this [Inser topic] becasue there are no technical aspects to my argument that are true.

Fight it on the rights issue, but don't fight it on a science issue when you do not understand the science.

Re:According to Rush Limbaugh ...

[SatanicPuppy]

Wow, I think this is the first time I've ever heard him say something nice about something black.

Re:According to Rush Limbaugh ...

[el_gato_borracho]

Rush Limbaugh does sound like a doofus when he tries to talk about science, but he is no racist. He consistently agrees with Dr King's ideal of judging people by the content of their character, not the color of their skin. Rush agrees with and supports people who agree with his political viewpoint regardless of skin color, and opposes those who disagree in like kind. A man who had a problem with black people would not let Dr Walter Williams guest host his show so often, would not interview Justice Clarence Thomas on his program, etc. It saddens me that politics has become so polarized that it is considered normal for people who never listen to Rush Limbaugh to "know" that he is a racist, plus get modded funny based on that smear.

Re:

[mrsquid0]

Someone needs to tell that caller about the difference between optical light and infrared light. I wonder if he has ever tried to boil coffee with a flashlight.

White paint or solar panels?

[Hankenstein]

Or we could put solar panels on roofs and convert the sunlight, that would ordinarily be
converted to heat, into electricity which I am sure we could find a use for.

Ridiculous

[jdb2]

Paint roofs white? With the efficiency increases in photo-electric technology, why not put solar panels on every roof? Not only would we reduce the amount of heat being re-radiated back into the atmosphere but, if done on a global scale, we'd eliminate one of the primary reasons for climate change in the first place : the burning of fossil fuels. And before you respond with "but it will cost too much and generate more CO2 than it eliminates" let me give you one word : Bootstrapping [wikipedia.org]. That's right -- Use the power from the existing global infrastructure for solar energy capture to build more global infrastructure for solar energy capture; That way, you would generate a minimal amount of greenhouse gases in the manufacture of new solar panels while at the same time creating a self-sustaining positive feedback loop wherein the more energy we can capture, the more energy capture infrastructure we can build, resulting in our ability to capture more energy.

I didn't RTFA but the summary sounds retarded.

jdb2

Great for Global warming....

[puppetman]

and sea levels, but not for the pH balance of the oceans, which are acidifying as they absorb additional carbon [wikipedia.org] from the atmosphere.

I remember reading about green roofs (growing plants etc on the roof of buildings) and the effect it had on temperatures when done in urban environments [wikipedia.org]:

Reduce heating (by adding mass and thermal resistance value) and cooling (by evaporative cooling) loads on a building â" especially if it is glassed in so as to act as a terrarium and passive solar heat reservoir â" a concentration of green roofs in an urban area can even reduce the city's average temperatures during the summer.

The Fairmont Hotel, here in Vancouver BC does this, growing herbs for the hotel kitchens. [uwaterloo.ca]

All the world Washinton DC

[flyingfsck]

Uhmmm, even painting the all the cities in the world mirror silver won't achieve anything. The world is much, much larger than the cities. Three quarters of the globe is covered in water. A miniscule part of the 25% that is land mass is covered in cities.

What about heat?

[IGnatius T Foobar]

This brilliant "idea" fails to take into consideration the fact that in the winter, sunlight falling on a roof does add to the heat inside the house. If the roof were a light color, that heat would have to be replaced by burning some sort of fuel. So unless you're in a location that never needs heat, the idea doesn't work.

Personally I don't believe there is such a thing as anthropomorphic climate change, but if I did, I would still keep my roof a dark color.

Or...

[Endo13]

it could be possible that the global climate change is just part of a natural cycle, and is actually a good thing. But hey, let's just ignore that possibility and try every idea no matter how stupid that we can possibly think of to "fix" it.

Seriously, if science has taught us *anything* it's that tampering with things we don't understand almost always makes them worse. Even when - actually, maybe that should be especially when - we're trying to "correct" a "mistake we've made".

Why not plant grass instead?

[phallstrom]

Wouldn't it be better to simply plant grass instead? Ignoring the problem of having to reinforce roofs that is...

I already did this ...

[Skapare]

... by painting all the solar cells on my roof white. But I'm gonna have to do this all over again because these solar cells aren't making any electricity.

Re:Run away Whitehouse

[Toonol]

We just up our deforestation, if that becomes a problem.

Re:

[Altus]

if only we could balance that out by somehow making some of those things dark. Its a shame that once you paint something white you can never paint it black again.

Re:Run away Whitehouse

[veganboyjosh]

So what you're saying is....

Once you go white, you never go back?

Re:

[ModernGeek]

Pffft, time to buy stock in companies that sell white paint.

Re:

[chrispitude]

You're worried about nighttime light pollution from white roofs reflecting more sunlight? (I doubt moonlight would be significant enough to be a factor.)

Re:Let's pave the road with solar cells.

[geekoid]

Yep. I have often speculated on using the road heat and vibrations to generate power.

I believe it is nothing more then an engineering problem at this point.