White Roofs to Fight Global Warming
by Michael Graham Richard, Gatineau, Canada on 12.16.05
We have covered green roofs extensively (see the many links at the bottom of this post), but we haven't given quite as much coverage to white roofs, which is unfortunate because it's one of these simple things that could make a big difference. New Scientist has a little piece on the subject: "Would it be possible to reduce the impact of the greenhouse effect by painting roofs of buildings white to reflect sunlight in the same way the polar icecaps do?" To answer that question, the the Earth Institute at Columbia University (New York) has undertaken the Global Rural Urban Mapping Project (GRUMP). Its results show that roughly 3 per cent of the Earth's land surface is covered with buildings.
The Earth has an albedo of 0.29, meaning that it reflects 29 per cent of the sunlight that falls upon it. With an albedo of 0.1, towns absorb more sunlight than the global average. Painting all roofs white could nudge the Earth's albedo from 0.29 towards 0.30. According to a very simple "zero-dimensional" model of the Earth, this would lead to a drop in global temperature of up to 1 °C, almost exactly cancelling out the global warming that has taken place since the start of the industrial revolution. A zero-dimensional model, however, excludes the atmosphere and, crucially, the role of clouds. [But!] It would be interesting to see if more sophisticated models predict a similar magnitude of cooling.
Of course, doing that would only be a way to gain a bit of time. On its own, it is no cure for our pollution and greenhouse gas problems.
A better use of roofs would be to use them as mini power stations by installing photovoltaic tiles. This would displace a significant proportion of the fossil carbon that we emit without relying on perturbing the Earth's delicate and complex climate system. Sure prevention is much better than uncertain cure.
So next time you replace the tiles on your roof or buy a new house, you know what to do (if you can't/won't get solar panels, white tiles or a green roof, at least try to get a light color).
::New Scientist, ::Cool Roofs, ::Green Roofs: A primer, ::Inhabitat on Green Roofs, ::First-ever analysis of green roofs’ ability to keep buildings warm in winter, ::Yet more on Green Roofs, ::Green Roofs by Earth Pledge Foundation
Wouldn't a green roof or solar panels also have the same heat-nullifying effect? Only instead of bouncing that energy back out they change its form?
All automobiles should be white as well ;-)
Nessie,
Toward the end of the post solar panels are mentioned.
As for Green roofs, they have many benefits, though not quite the same as white roofs. They help with water run-offs, isolate buildings from heat, filter some of the pollution in the air and such.. But they are not as reflective as white roofs.
But either a white or green roof (with solar panels, in the best case) would much better than the dark roofs most buildings and houses have.
This is true where cooling houses is an issue. In colder climates the effect is at worst adverse at best horribly unpleasing for the eye. Might I have the multi colored corrugated iron roofs of Reykjavík any day before painting them white.
The study also neglects the secondary effects of such a plan. Where's the greatest concentration of rooftops? Cities. Where do we burn the most electricity for mechanical cooling? Same place. Painting the rooftops white instead of tar black or dark shingle, not only would the air around the city see a cooling change, it would also reduce the energy needed to cool the house itself.
I've speculated on this riding the elevated mass transit system here in Philly, looking at all the tar-covered rooftops. Instead of a more 'global' study on this topic, I'd like to see one that just considers an individual major city.
I grew up hearing that roofs in colder climates were traditionally dark to absorb heat to lessen the amount of fuel needed to heat the building. If the additional added energy needed to heat the house to the same degree is not from a green source wouldn't painting the roof white contribute to global warming more than detract from it. White roofs in and buildings are very sensible for hot climates and they are also beautiful.
Are copper and zinc roofs also highly reflective? If so, they might be an attractive alternative to white roofs, especially on older houses on which they are historically appropriate.
Even though solar panels convert some of the energy to electricity, they still get quite hot - around 30 degrees C above ambient temperature if memory serves correctly. However, you could take advantage of this through coupling solar panels with a solar hot water system by simply running pipes underneath the solar panels, for example. This puts the heat to good use while reducing the temperature of the solar panels (which is an added bonus since solar panel efficiency is negatively affected by higher temperatures) and the building's cooling load.
But if you don't have the $$$, white (or green) roofs are certainly a nice path ;)
How do you model global warming without modeling the atmosphere? Answer: You can't.
Energy that's reflected by roofs passes through two different air masses. How's that going to decrease global warming exactly?
People who want to decrease the impact of humans on Earth need to understand science.
"How do you model global warming without modeling the atmosphere? Answer: You can't.
Energy that's reflected by roofs passes through two different air masses. How's that going to decrease global warming exactly?"
I think you're under the impression that these scientists claimed things that they haven't (yet) claimed;
Their model was for how much light is reflected off the planet, and how white roofs could increase that amount. In turn, they suspect that more light reflected could have an impact on global warming. They never claimed to have incorporated their white roof variable into a global warming model (but they are working on it).