You can observe this effect today in Spain already.
The region around Almeria is covered by greenhouses that use white plastic sheets to protect their crops. The region has effectively cooled by 0.3 degrees whereas other areas have increased 0.5.
These surfaces at scale will be a game changer for fighting climate change. They seem like magic. Here’s a key quote from Wikipedia:
> Some estimates propose that if 1–2% of the Earth's surface area were dedicated to PDRC that warming would cease and temperature increases would be rebalanced to survivable levels.
Solar near people and PDRCs away from people (where solar is impractical) along with a reduction in Carbon is a feasible plan today.
Cover 1-2% of the Earth's surface with solar panels and you have so much spare energy that you can do all kinds of crazy stuff, like sucking carbon dioxide out of the air and turning it to diamonds for fun.
Solar panels are limited by cost. If this cooling ceramic is a better version of the barium sulfate thing (i.e. just an extremely cheap-to-produce material that's very white) then this is viable because it doesn't cost hundreds of dollars per square metre to manufacture.
Its main limitation would likely be construction costs, which is a problem solar panels are already starting to run into. Although construction of solar requires setting up cables and not e.g. accidentally snapping hundred-dollar solar panels in half (which would be a non-issue for barium sulfate, since it's dirt-cheap and basically just white paint anyway).
A quick calculation on Wolfram Alpha: to cover 2% of the world's surface at 50EUR/m2 would cost roughly 540 trillion euros, or 5.5 years of current world GDP.
Where I live solar panels are limited by regulations. They pay for themselves after a couple of years so people would plaster them literally everywhere the sun shines if they were allowed to. White paint otoh probably has worse ROI.
The "white paint" parent is referring to can passively cool the surface a few degrees below ambient temperature 24/7 (yes, even at night). I could imagine worse investments.
A negative ROI (return on investment) suggests it won't pay for itself ever, be that in cash or carbon.
If you're actively trying to cool the building then painting it in something that lowers the energy needed to cool it. And as were just talking about paint, carbon and cash cost is likely to be low relative to savings.
So no, painting all houses in this stuff might not reverse global warming, but that wasn't what we were talking about.
Yup. We have more than enough harnessable solar power to allow every single person a clean energy budget higher than a typical American, offset all other industrial carbon production, and start to unwind the last century of humanity's carbon impact.
But instead of working towards that end-state, a lot of people (even people on this site) seem to be more interested in shaming others into using less energy, and attacking others for "immoral" uses of energy.
But currently we aren't on a course to actually unwind that carbon production in time.
It's like saying there's an oasis 2 days walk from here, so don't worry about having a shower and possibly using all your drinkable water. You still need to save enough water to actually get to the oasis, and at the moment, we're kinda sorta having a conversation about whose job it is to actually make the trek, so in reality it's going to be at least another day before everyone decides that they need to start marching, and as we only currently have 2.5 days of drinking water. That shower is really irresponsible.
To put that in perspective, in 2014 the estimate was artificial structures covered 0.6% of the Earth's surface. It might take a while to double the amount of buildings, roads etc. and cover it all with PDRCs
Quoting https://science-atlas.com/faq/how-much-of-the-earth-is-inhab...: "According to the FAO Global Land Cover SHARE database, produced in 2022, 0.6% of Earth’s land surface is defined as ‘Artificial surfaces’. Artificial surfaces include any areas that have an artificial cover as a result of human activities such as construction (cities, towns, transportation), extraction (open mines and quarries) or waste disposal. This figure gives us an estimate of roughly 900,000 km2 of human-covered land worldwide."
Iron fertilization of equatorial oceans would make for very high albedo algae blooms. The ocean absorbs the vast majority of absorbed solar radiation. It has been pointed out that at low angles it reflects almost all light, but that is when the energy has gone through the most atmosphere and the water or land would absorb much less anyway. Napkin math scaling up previous fertilization experiments indicates about 1.5 billion USD per however long the blooms last, to trigger a snowball earth. We'd stop when it got cold enough.
Easily verified from ice core data. The UN Convention on Biological Diversity banned large-scale iron fertilization experiments in 2008. Cynically, I don’t think anyone’s figured out how to make money on it either.
If the 1.5 billion USD per event estimate is correct, it has to be banned because it's cheap enough that people don't need to make money on it — it's about what Oxfam raises every 18 months.
Or a winter day at high latitudes. I'm convinced the Illuminati (it's in the name, no?) arranged the roads so you're always driving into the sun wherever and whenever you're going.
To save people a bunch of time: no, you can't. The best he comes up with is something incredibly fragile that is damaged if you so much as look at it wrong, and any sort of protective covering or coating dramatically alters its effectiveness.
Nobody has come up with a DIY "paint" or coating that is durable.
> This is why it feels colder on a cloudless day or night.
This is not entirely true. It's not because your thermal energy is radiated to something colder, but rather because clouds contain and reflect the thermal energy that would otherwise be lost to space.
I’m just waiting for a version of a vacuum thermos that keeps my drink hotter, longer. Put this on the inner side of the outside surface and paint the inner side of the inside surface with the blackest black available. Almost like a thermal diode. Reverse the sides and you have a cold-cup instead…
This would not work in your thermos! This material is reflective in the visible but emissive in the infrared. The only thing that matters in the thermos is being reflective in the infrared.
Thermodynamics does not permit a thermal diode to exist.
I think it's even simpler than that. Any black body that is colder than its surroundings heats up. Any black body warmer than its surroundings will cool down.
This thermos would only keep your coffee hot if you dropped it into a furnace.
You could make a colored flask which absorbs visible light (from the sun) but reflects thermal wavelengths (from the drink). But due to infrared leakage and thermal conduction, I don't know if it would keep drinks above 100 degrees F for anywhere near as long as a standard vacuum flask.
The neat thing about wearing white in the desert is that it keeps you cool during the day and warm at night. Wearing black does the opposite.
A perfect black surface on a spacecraft can do more than charcoal black paint, but only by a matter of degrees. If memory serves its less than a 2x multiplier between off the shelf and exotic materials. But when ounces cost thousands of dollars, you’re going to go exotic.
My "solution" is a $5 mug heating pad that pulls 16W. It only heats when there's a weight placed on. Probably accounts to 10kWh for the whole year to keep a warm cup of coffee ready for the whole day.
The material is apparently hydrophilic, so it can absorb a lot of water. That means things like algae and gunk will fill the material, rendering it less effective.
From reading through the supplementary materials for the paper [0], it seems that the authors are aware of this flaw and they found a way to make it hydrophobic. The approach they tested involved soaking the ceramic in a bath with a commercially available fluorosilane [1] that is used to make things superhydrophobic. Fig. S20 in the supplementary materials has a chart that shows the treated ceramic being very good ("solar reflectivity...remains at ~99.0%") but not quite as stellar as the untreated ceramic.
Most of these clever optical solutions for all of our problems have an "it gets covered in dust eventually" problem. You can also get the opposite effect -- heat absorption with little radiative heat loss -- using a very thin layer of silver, but again, dust.
How much maintenance does this take to keep its reflectivity? Does it get colonised by algae? If it needs to be scrubbed with bleach once a year, I can see that being an issue.
Aluminium plate painted with this paint is cooler when exposed to the sun not only than unpainted plate but also ambient air which feels really magical for me.
> If I can see it, that means that it's radiating in all directions, not just into space
That depends on what you mean by "see". If you paint a square on a white paper with a magical paint that absorb 100% of the light, you can still see that there's a black square, because it's sitting on a contrasting background.
Even if the material is perfectly radiating everything to space, i.e., the roof sends no light to your eyes, it's still just a patch of blackness among normal things, and you can see the shape of it, just like a puddle on the road at night, as you walk with your back to the moon.
It's about the angle of reflection. When light reflects off a surface, it leaves at an angle equal to the angle it comes in at.
Most of the light hitting the roof will be reflected back up into space. Some small percentage of it will scatter and disperse into all other directions.
If you were in a plane at exactly the right angle between the roof and the sun, you'd see a glare much stronger than you'd see at street level.
Google "diffuse reflection" and "specular reflection" if you're interested to understand why.
Things do not radiate uniformly, neither behave like mirrors (specular). The truth for most objects is somewhere in between.
You can see it with a plastic object as well, when it is positioned so that the angle to the normal vector (a vector perpendicular to the surface) of the light source and to your eye are the same (as in, you would be able to see the light source if it were a mirror), you see much more light than when you are simply looking at it "from the side".
I'd imagine it's (total amount of sunlight hitting the visible portion of that roof) * (… the solid angle the window occupies, relative to the roof?)
The first portion of that equation is hot: roofs have a lot of sq. ft.'age, and a fair bit of sunlight strikes them. But the second part is well the other direction: the window probably doesn't occupy a whole lot of the field of view of the roof: i.e., mostly, any ray emitted randomly from any point on the roof is likely going to be skyward, so assuming it emits the heat/light out equally in all directions, your window only gets a small fraction.
The portion coming in your window doesn't go back out to space but I don't think that's a big deal?
It doesn't need to go back into space. If you don't want the scattered sunlight to heat your house, you can always add the same ceramic to your house...
I'm pretty sure that doesn't work. The surface works because it's emitting a band of radiation that the atmosphere is mostly transparent to. If it sees radiation in that same band it's going to absorb it, not emit. Point enough of these at each other and you'll approach zero.
The material works by having very low emissivity / absorptivity at sunlight wavelength so that sunlight is scattered back out, and by having high emissivity at typical earth temperature blackbody peak wavelength, so it radiates out heat effectively.
Sunlight that is scattered off the roof can scatter back off other roofs before heading into space. Likewise radiation that is emitted by the roof can be absorbed and then re-emitted by other roofs before heading off into space. Neither of these preclude the roof from doing its job.
At the end of the day, the roof will effectively reflect back sunlight from the high temperature sun, while radiating infrared radiation into the low temperature sky, and have a neutral energy balance with the surrounding earth / houses / trees / objects which are at a similar temperature to it.
> Sunlight that is scattered off the roof can scatter back off other roofs before heading into space.
… but that's not what they're asking about?
Imagine you're standing in a second story window, looking out. Out the window, you're seeing your neighbor's roof, coated with this stuff. A lot of sun is hitting that roof — How much heat is coming in through that window, off that roof?
There have been stories in the past of reflective surfaces cooking nearby apartments, so I get the concern. I think in this case it boils down to it not being reflective, mostly, so it's fine.
You’re missing the point here. Almost willfully so.
Two pieces of this material in an overlapping field of reflection are putting out exactly the wavelength the other will absorb. I can’t defend my building from being baked by yours by coating it with the same stuff. I am simply going to return the favor in the process.
Not to mention the big problem of creating a new case of the haves versus the have-nots.
Less than 70% on non-commercial structures. And on commercial structures the roof can be a negligible percentage of the total building envelope.
This is cool stuff, but it’s just stuff. It’s not a silver bullet. We here are all old enough, many of us by half, to no longer get sucked in by magic thinking.
The bulk of the roof can be assumed to be oriented to the sky, or it wouldn't get much sun and be of no concern. So it will radiate towards the sky mostly.
The infrared radiation will indeed go out in all directions. The way I understood it there will be less of it, because the roof is cooler. So if this material replaces a traditional surface, you will get more visible light scattered your way, and less infrared light.
What does it mean for a layman? It says it reflects around 99% sunlight and 96% infrared. Does it mean if placed outside in hot summer days the underside will stay at ambient temperature?
It'll likely stay a few degrees below ambient. Ordinarily, that doesn't happen because the surroundings are emitting and absorbing infrared roughly in balance with things at the same temperature, but if you can make a material that emits most of its infrared at a particular frequency that the atmosphere is nearly transparent to, its heat will leak out into space.
This could be very interesting material for surfaces in greenhouses where you want to have as much light as possible but during the summer don't want to have the heating effect.
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Edit: in case it's helpful, here are some examples of good comments you posted:
Please do not do this. Title reads: "New cooling ceramic can enhance energy efficiency for the construction sector and help combat global warming". Not sure how you leapt to the conclusion that that's all we need? And one of the people who you feel have no clue is this person: https://www.cityu.edu.hk/see/people/prof-edwin-chi-yan-tso. Are you more credible?
Just like every silver bullet solution out there, if we dedicated all of the efforts of humanity to making this stuff, and possibly keep climate change at bay. Alternatively, we could be more realistic and do more than one thing, and materials like this might be a part of the solution.
The region around Almeria is covered by greenhouses that use white plastic sheets to protect their crops. The region has effectively cooled by 0.3 degrees whereas other areas have increased 0.5.
https://www.agroberichtenbuitenland.nl/actueel/nieuws/2019/0...