Comment by Qem
2 days ago
> The United Nations (UN) believes there are 4B buildings on Earth. This week, a dataset called "GlobalBuildingAtlas" (GBA) was published by researchers at the Technical University of Munich (TUM) that attempts to estimate this number at being closer to 2.75B.
If we painted the roofs on all of them white, by how much would the temperature of the planet drop?
Probably not as much as if we “painted” them black with solar panels and used the resulting electricity to displace fossil fuel burning.
There was a good study on this a few years ago that ran the numbers on this and landed on white paint for residential homes as the best option, for a few reasons, if I remember correctly:
- Installation, maintenance and transmission costs are lower when solar is aggregated on farms - Solar offsets air conditioning, but that moves the heat outside. White roofs reduce the need for AC, which helps significantly with urban heat scenarios
A quick search yields a UCL study, which supports the lower claim: https://phys.org/news/2024-07-roofs-white-city.html
A good percentage of Pakistan did this recently and removed 35% of demand off of their grid https://www.ted.com/talks/jenny_chase_solar_energy_is_even_c...
I would love to have an air conditioning / cooling solution that is directly linked to solar panels with no batteries involved. Like the sun shines, we get electricity, we do the work. My main goal for this thought experiment is to come up with uses of solar electricity that is resilient to the unpredictable and unreliable energy generation from solar. Thoughts?
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I'm now wondering if painting a roof white is better than covering the same roof with solar panels and using that to drive air conditioning (in the house). My intuition is that painting it white must be vastly more environmentally friendly, although it probably doesn't reduce the temperature very much compared to aircon.
There are certain materials that aren't just white but also specifically radiate heavily in IR bands that the atmosphere is particularly transparent to and so can actually stay sub-ambient temperature while in sunlight. See, for example, https://onlinelibrary.wiley.com/doi/full/10.1002/eom2.12284
But adding conventional AC is never going to cool down the world.
AC doesn't make it cool it merely transfers the heat to the outside in an energy efficient manor. The emerging tech is special coatings that convert heat to an infrared frequency that easily escapes the Earth's atmosphere.
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It's worth factoring in that solar panels also provide solar insulation to the roof by effectively shading it, ie the sun shines on the panels and there is an air gap between the panels and your roof.
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Does the house already have AC or not? And are you talking about indoor temperature or outdoor temperature? Also many places are cold. Running AC would make it worse.
there is a cool project that explores this topic: https://coolcolors.lbl.gov/
I think we should do more albedo engineering. like white roads and car roofs.
Back-of-the-envelope - Road area. World road length ≈ 60–70 million km. Using an average paved width of ~8–10 m ⇒ area ≈ (0.9–1.3)×10¹² m². Earth’s surface is 5.1×10¹⁴ m², so roads cover ~0.09–0.13% of the planet.
- Albedo change. Dark asphalt is ~0.05–0.10. “White” coatings can push toward ~0.4–0.6 (fresh), but weathering quickly dulls them. So a plausible Δalbedo for roads is +0.2 to +0.5.
- Global albedo change. Δα_global ≈ (road fraction) × (Δalbedo_road) ≈ (0.001)×(0.2–0.5) ≈ +0.0002 to +0.0005.
- Radiative forcing. Globally averaged incoming sunlight ≈ S₀/4 ≈ 340 W m⁻². Forcing from an albedo change is ΔF ≈ −Δα_global × 340 ≈ −0.07 to −0.17 W m⁻².
- Temperature response. Using a standard sensitivity ~0.8 °C per W m⁻² (≈3 °C per CO₂ doubling): ΔT ≈ −0.05 to −0.14 °C at equilibrium.
White roads could potentially be blinding, but yeah something lighter than what we do currently could be very worthwhile. It'd have much higher nighttime visibility too.
I'm thinking about light colored roads that seem to be made of concrete. See them here and there. Seemed to be more of them when I was a kid.
Wonder if that would make a substantial difference? Much brighter than asphalt but not bright enough to bother drivers.
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> White roads could potentially be blinding
Hell I was just walking down the street a minute ago and thinking the same! It's October ffs! (It IS October right?)
Teslas will start crashing like there’s no tomorrow.
So nothing much will change?
Painting roofs (or even all man-made surfaces) white wouldn't do much globally at all, but it might reduce the urban heat island effect. But probably (speculating a bit here) not quite so much as creating more green spaces (or green roofs, for that matter).
I would guess not that much - certainly fractions of a degree - because the proportion of the planet's surface is still relatively low, and as much as 60% of that reflected light would be scattered and absorbed by the atmosphere.
It'd have a much bigger impact if all those roofs had solar panels, and the resulting electricity was used to replace carbon-emitting energy sources.
Paris and other climate accords have much ado about fractions of a degree, leading me to believe that that's highly consequential.