July 19, 2010
Higher Albedo Roofs Could Cool Planets
Raising the albedo (reflectivity) of roofs and pavement with lighter colored and more reflective material could delay the effects of higher atmospheric CO2 by about 2 years.
In the latest study, the Berkeley Lab researchers and their collaborators used a detailed global land surface model from NASA Goddard Space Flight Center, which contained regional information on surface variables, such as topography, evaporation, radiation and temperature, as well as on cloud cover. For the northern hemisphere summer, they found that increasing the reflectivity of roof and pavement materials in cities with a population greater than 1 million would achieve a one-time offset of 57 gigatons (1gigaton equals 1 billion metric tons) of CO2 emissions (31 Gt from roofs and 26 Gt from pavements). That’s double the worldwide CO2 emissions in 2006 of 28 gigatons. Their results were published online in the journal Environmental Research Letters.
“These offsets help delay warming that would otherwise take place if actual CO2 emissions are not reduced,” says Surabi Menon, staff scientist at Berkeley Lab and lead author of the paper.
The benefits of this idea go beyond global warming. Another advantage would be cooler cities in the summer. Don't you just hate hot black pavement in the summer? The dark color of the pavement does less to warm up cold winters because there's less sun in the winter. So dark colors in building materials and pavement tend to intensify the difference between summer and winter weather.
1) the 57 GT of CO2 would have any net global warming effect
2) the model used to calculate the offset etc is accurate [plus or minus 4,000% or what ?]
3) the inherent CO2 production used in the production of 'reflective' materials would have relatively little CO2 'cost'
Like the result of all models of chaotic systems, the information could be useful for identifying relative magnitude of constituent parameters but not so useful as a predictive tool.
Your readers should understand that such exercises are only slightly better than WAGs or thought experiments.
Might a building in say, northern Minnesota benefit more from a dark roof to absorb heat in the non-summer months (to mitigate heating costs), whereas a house in Texas would benefit from a more reflective roof (to mitigate A/C costs)? Any studies on this sort of thing?
Does angle of incidence have much affect, or is it more of a black body radiation problem? You could have corrugated metal roofing that basically takes the other two sides of the right triangle with the roof being the hypotenuse. The flat side facing up would be white, and the vertical side facing south would be black. Perhaps a slight overhang to insure that the southern exposure only gets direct sunlight in the winter months when the sun's track is lower.
Someone should develop roofs with adjustable albedo. Summer? White. Winter? Black.
Absorbing heat on the outside won't help as much if the building is well insulated. The heat won't get thru. During winter the light will shine only a small number of hours each day too. So I do not see a big benefit from sunlight heating up the outside surfaces of a building during short winter days.
Dowland, there is a world of info available concerning "Passive Solar" building design. Sometimes buildings are DESIGNED to absorb heat in winter and avoid heat gain in summer. In reality, Tom, every well insulated building in northern Minnesota will have a WHITE roof for most of the winter --- it's called SNOW - rofl
Well, I for one see a problem with light-colored and more reflective highway pavement! People crashing and dying all over the roadways as they are blinded or dazzled by light reflecting from the pavement! If this isn't just nutty.
Doug, concrete is far more reflective than asphalt, but doesn't seem to blind drivers.
In Phoenix, the summer days are scorching but the nights are pleasant. Well, they used to be: So much of the desert has been paved that the city has become a big heat sink, absorbing heat in the day and radiating it in the night. There are days in the depth of summer where the thermometer barely dips below 100F even in the middle of the night.
I wonder if higher albedo roofs and roads could make Phoenix summer nights bearable once more.
Regards adjustable albedo: That's at least doable with windows. Think of the sunglasses that adjust their tinting based on the amount of light hitting them. What's really needed: tinting that adjusted based on temperature.
But I do not see as much value in making the house's outer surface black. A house ought to have enough insulation that it does not lose much heat (or let in much heat) anyway. The main variability ought to be in how much of the light from outside gets inside. That's controllable in a variety of ways such as with awnings and shades.
Doug, 2 things:
1. They use whitish concrete all over L.A. and that's not an issue mainly because drivers usually wear sunglasses, and their eyes get less total light to overwhelm them because they are in an otherwise darker car interior. (White reflections all over the place overwhelming my vision is a big issue for me in Las Vegas on foot, however; I need sunglasses more here than anywhere else I've lived.)
2. That white pavement doesn't stay white for long anyhow, as the steady accumulation of oil and tire rubber takes care of that right quick.
uhmmm gentlemen? is there any concepts of the global phenomenon solver that has been develop and available now for temporary usage?