Question: Whiter roofs and paler pavements (seriously)?
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Answer #1:
Well it might help a little bit in cooling cities but on a global scale it will do nothing.Answer #2:
The results of the study are plausible. The study implies that the urban area is 1.2% of the earth surface, or about 1/2 of the US density.Click Here
The calculated radiative forcing -4.1 W/m^2 is correct.
A larger offset could probably be achieved by using crop genetically modified for increased reflectivity. The simplest mechanism: increased meso scale surface roughness would reduce photosynthetic efficiency.
Answer #3:
That's an impressive figure. Of course it's a scenario where every roof is white and bit of pavement is lighter in every large city, but still, it shows that moving in that direction is worthwhile. Painting roofs white is simple enough, and it's something new construction should take into consideration.Perhaps not coincidentally, Steven Chu has announced new initiatives to promote and install “cool roofs” on DOE and other federal buildings.
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Incidentally, the roof on my house is white!
@ gcnp - pfft, only about a third of my roof is covered with solar panels. The rest is still reflective. And as I recall, the decreased albedo is more than offset by the reduced CO2 emissions from energy production, by a long shot.
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"So you win on the solar panels."
Score!
Answer #4:
The problem is that it isn't just the total forcing, but the geographical distribution of that forcing. Since the forcing from CO2 isn't uniform globally:Click Here
so the distribution of the forcing from white roofs has to match the CO2 forcing for the two to offset. The situation becomes even more complicated if you take things like aerosols and clouds into account. See here:
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Steve Ghan, at PNNL, has discussed this issue in the context of geo-engineering solutions to climate change, which are similarly idiotic.
@Dana: Your roof isn't white, it has solar panels on it. It's actually contributing to the radiative forcing of the planet and since the conversion efficiency of the solar panels is low, it probably contributes more positive forcing from the lowered albedo than it gives in terms of carbon offsets from the electrical generation. This is why there are no practical solutions to mitigate radiative forcing that do not start from the premise we have to reduce our energy usage by probably a factor of 10. Any solution that doesn't start from that point is a joke, but since any solution starting from that point is ludicrous in its practicality in terms of getting people to voluntarily adopt it, the situation is essentially hopeless.
@Dana: I had forgotten about that. Also, it appears the lifetime of a solar panel is longer than its payback time:
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So you win on the solar panels. But I am right about the geographical distribution issue. You have to balance the total forcing and at the very least the latitudinal distribution or there will still be effects on climate.
Answer #5:
All things considered, a home is constituted as a envelope. The direct effects will never be apparent, the indirect are measurable using load calculations. If you reduce the internal heat load by ~20% that's a indirect savings on conventional energy usage(big pic). Until the liquid in solar panels obtain a constant 120 degrees F they will never have a direct payback and will always be a supplemental and limited source of energy.ed: Should have said for a cooling load, heating will be the opposite and depends on your geographical local.
Answer #6:
- the first thing to be considered is area. # of sq feet / sq miles. In that respect, roads win hands down. Roofs are good, but there's far more road.- However, the problem is that it's not easy to make a white road. And when you do, the combination of leaked oil, and tire marks, turn it black far to fast.
- Concrete roads are good, but hard to keep clean. In addition to global warming, it takes far less energy to light them because they make so much better use of light. I'd be surprised if someone hasn't gone looking for how to create white roads, and not come up with a good answer.
- Recently when i got a new roof, i asked about what options were available for a white roof. It may be that i didn't ask enough, or the right, people, but the answer i got was that there really wasn't a good option.
while i think it's a good idea, i've not heard of any good ways to accomplish it.
Answer #7:
- the first thing to be considered is area. of sq feet / sq miles. In that respect, roads win hands down. Roofs are good, but there's far more road.- However, the problem is that it's not easy to make a white road. And when you do, the combination of leaked oil, and tire marks, turn it black far to fast.
- Concrete roads are good, but hard to keep clean. In addition to global warming, it takes far less energy to light them because they make so much better use of light. I'd be surprised if someone hasn't gone looking for how to create white roads, and not come up with a good answer.
- Recently when i got a new roof, i asked about what options were available for a white roof. It may be that i didn't ask enough, or the right, people, but the answer i got was that there really wasn't a good option.
Answer #8:
<<The problem is that it isn't just the total forcing, but the geographical distribution of that forcing. Since the forcing from CO2 isn't uniform globally so the distribution of the forcing from white roofs has to match the CO2 forcing for the two to offset.>>That is not correct. Even if there were NO carbon dioxide, increased reflectivity would cool as planet.
Indeed if the white paint reflects infrared it would be more effective in regions with *less* CO2, because less of the reflected infrared would non-escape.
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