One little fact. There are roughly 100,000 square miles of asphalt road, parking lot and roof in the US.
The average albedo(reflectance)of the earth is 34%.
The average albedo of asphalt is 5%!
95% of the Solar radiation falling on asphalt gets absorbed or re-radiated in wavelengths that are trapped by greenhouse gases.
5% gets reflected back into space.
When Sunlight falls on to snow or a WHITE reflective surface 15% or less is absorbed,
85% or more gets reflected back into space at the same wavelengths that came in and is NOT absorbed to heat the atmosphere.
The whole phenomena behind the effect of greenhouse gases is that visible and ultraviolet light are not absorbed by the atmosphere on the way in. The impinging energy is reflected and absorbed at the earth's surface, The energy that is reflected leaves into space. The absorbed energy is re-radiated as longer wavelength infrared that is then absorbed by greenhouse gases such as CO2 and Methane and it is this absorbed heat that contributes to global warming.
Now you can see there are two pieces to this puzzle the reflection/absorption ratio part and the infrared absorbing greenhouse gas part. The ugly thing about asphalt is that it increases the energy re-radiated at wavelengths absorbed by greenhouse gases by 50%.
A given CO2 concentration is roughly 5 times more effective in heating the planet in the presence of black asphalt than white concrete. Considering the 100,000 square miles of asphalt and asphalt roof in this country this is a huge heat load increase and one that has a relatively simple solution. Coat the asphalt with a white reflective coating.
White roofs would offset warming, researchers say
According to Hashem Akbari, a physicist with the Lawrence Berkeley National Laboratory, a 1,000-square-foot roof - the average size on an American home - offsets 10 metric tons of planet-heating carbon dioxide emissions in the atmosphere if dark-colored shingles or coatings are replaced with white material.
Globally, roofs account for 25 percent of the surface of most cities, and pavement accounts for about 35 percent. If all were switched to reflective material in 100 major urban areas, it would offset 44 metric gigatons of greenhouse gases, which have been trapping heat in the atmosphere and altering the climate on a potentially dangerous scale.
That is more than all the countries on Earth emit in a single year. And, with global climate negotiators focused on how to offset a rapid growth in emissions, installing cool roofs and pavements would account for more than 10 years of emissions growth, even without slashing industrial pollution.
I had been a little leery of the area and insolation numbers,
in light of this guy's paper,
but the guys below working out of Japan and the UK independently came to a similar conclusion to that of the Berkley paper, involving roughly the same area.
Fix For Global Warming? Scientists Propose Covering Deserts With Reflective Sheeting
It can work, but if reflective surfaces are to work, we have to also control particulate pollution such as soot which increases the absorbance of surfaces.
Reflective paint, with the little glass beads as in road marking paint is expensive. But since it can demonstratably reduce the heat island effect,(put a couple of sheet of black paper on the snow and watch it sink if you don't believe me) then getting rid of the black would be a good expenditure to include in the the coming infrastructure projects.
This does not mean that we should continue to spew carbon monoxide into the atmosphere willy nilly, but this means that we are not helpless. That there IS a short term solution that can be implemented within a year will reduce the heat load and at least give us time to get emissions under control before the polar bears become extinct, the Seychelles drown and Olrando becomes beach front property.
The question here is: if the math makes sense, we can do it, then what the F8$K are we waiting for?
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