Scientists Develop "Paint" To Help Cool the Planet 145
AaronW writes Engineers at Stanford University have developed an ultrathin, multilayered, nanophotonic material that not only reflects heat away from buildings but also directs internal heat away using a system called "photonic radiative cooling." The coating is capable of reflecting away 97% of incoming sunlight and when combined with the photonic radiative cooling system it becomes cooler than the surrounding air by around 9F (5C). The material is designed to radiate heat into space at a precise frequency that allows it to pass through the atmosphere without warming it.
What about for cars? (Score:2, Interesting)
Cars being greenhouse ovens is a terrible issue. Not just because it's uncomfortable getting into the car on a hot day, but because people accidentally kill pets and children by leaving them in a hot car every year (and others not so accidentally). Surely there's better tech than what we use today to prevent our automobiles from becoming lethal ovens.
Oven Tech (Score:5, Funny)
Certainly there is. You can just cook your kids and pets at home, no need to waste the gas going out at all. Home ovens have been large enough to do this for decades now. People are so wasteful!
--Hannibal
Vegetarian Stew Recipe (Score:5, Funny)
Vegetarian Stew
Serves 20
Peel, core, and slice one vegetarian.
Place in trunk of black car for two days.
Season to taste.
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Now, see!?
That is the kind of straightforward and direct, logical, practical, problem-solving engineer-style thinking /. *used* to be known for right there, something that seems to have almost disappeared from /.!
Bravo Sir, bravo!
Strat
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Srsly. Any other colour (OK, I'll exclude pastel whites ; say anything with an albedo of less than 90% or so) would absorb more light/ heat than this tailored IR radiator can emit to space.
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You need to read Gene Weingarten's Pulitzer-prize winning article on this before you hurt someone: Fatal Distraction [washingtonpost.com]
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Yes... (Score:5, Insightful)
Scientists Develop "Paint" To Help Cool the Planet
They're calling it "White".
Seriously, though, it's a mirrored silver paint with some nanoparticles mixed in to make it even cooler (pun intended). But if people aren't painting their roofs white and silver today, do they really think their paint will change that?
On the other hand, a radiator that reflects sunlight sounds promising for other applications, like heatsinks for space probes.
Re:Yes... (Score:5, Insightful)
Would people paint their roofs to save money, you bet they will but how cheap is the paint, how clean does the roof need to be, how cheap is it to apply and how long will it last. I would have no qualms about painting my roof white, as long as I can get it done cost effectively enough. Of course one other thing, how well does it perform after it is no longer pristine, how self cleaning is it with rainfall or do I have to get up there and clean it every once a month to maintain performance. When it comes to using white as default for roofs, it is easy enough for many countries to legislate that for all new structures that is mandatory and provide subsidise for existing structures.
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White steel roofs last 20 years without problems. Dont use this junk paint, get a standard white powdercoated steel roof and call it done. Plus you end up with a roof that will last over 2 decades and eliminate leaks, Ice buildup, etc....
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Is it ok if I keep my slate roof instead which has lasted about 100 years?
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Only if it's white. Problem is American homes are not built strong enough and will crush instantly under the weight of a Slate roof.
We build complete crap here in the USA.
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I assume the governments would then assume liability for all the car accidents caused by drivers blinded by the glare. There are many reasons white roofs haven't really caught on, and a simple efficiency boost won't fix things.
If you're looking to paint your roof, I'd recommend modern coatings which are IR-reflective but absorb visible light. Some reflect UV as well.
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White roofs are very common where I live in sunny Brisbane Australia. My own is white with the beautiful name of "Sea Spray". Though lots of people opt for dark coloured tiles, it seems to be the norm for tin roofs to be light.
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Why paint? Presumably we're talking about houses here (unless we own apartment complexes). Instead of white paint, buy light colored shingles or ceramics.
I would imagine the first couple on the block will be eye sores, but as more people get into it, they'll look more in place.
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Cost efficiency is the driver, by the way cost efficiency does not mean cheap it means how much performance you get for your investment, where sometimes paying more is more cost efficient. Why paint, because replacing say roof tiles is very expensive. Not that this is new, a 30+ year old industrial sub-division created by the South Australian government had already mandated all buildings have white roofs, so nothing new (for the crazies, no it did not cause planes or cars to crash, especially considering t
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and you nailed it. This "paint" is raging BS. simple latex white paint is exactly as effective as this paint is. so buy a $6.95 gallon of bright white latex and ignore this snake oil.
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You're missing the point - if you read the article the reflectivity is actually a bonus feature, the primary feature is that it radiates heat at a frequency to which the atmosphere is transparent, meaning that you can potentially use radiative cooling during the day in normal conditions almost effectively as you can at night in the desert (or in space). And if you've ever been in a non-tropical desert at night you know it can get cold *fast* once the sun goes down, even in the summer.
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If you bothered to read TFS you would see that they are claiming that, unlike normal white paint, their coating reflects the heat in a way that prevents it heating the atmosphere so much. So they are saying that removes more heat from the planet than normal white paint does.
They are not claiming it is significantly better than white paint at cooling your house, they are claiming it is significantly better at cooling the planet and reducing air temperature in urban areas.
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and if you understood simple math you would know that if every building on Earth were painted with this stuff it would have a negligible effect on the temperature because the area isn't that great.
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If you bothered to read the article, you would see they talk about using Titanium Dioxide. the WHITE COMPONENT IN WHITE PAINT.
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and you nailed it. This "paint" is raging BS. simple latex white paint is exactly as effective as this paint is. so buy a $6.95 gallon of bright white latex and ignore this snake oil.
Outside the scope of "does the article's material do what it says", this comment is still potentially false. Around half of the sun's energy that reaches the surface of the earth is not in the visible spectrum. "Bright white latex" paint is designed to be highly reflective in the visible spectrum, but makes no guarantees outside of that. You are much better off purchasing paint specifically designed to be highly reflective across a much broader spectrum.
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a radiator that reflects sunlight sounds promising for other applications, like heatsinks for space probes.
Sounds more like an oxymoron: radiation and reflection are two related but different processes. A perfect radiator reflects nothing, and a perfect reflector radiates nothing.
Parts of spacecraft that need to be cold (like infrared telescopes) are cooled by radiators that are kept pointed at dark space, with reflective shrouds that keep sunlight off them.
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I don't mind when people state clearly that they don't really understand the absorption & radiation equations, but it does kinda piss me off when these same people pontificate as though they did.
Here's how this new microlayer thing works:
First, it's highly reflective in the visible. That keeps a lot of energy from every entering (and being absorbed in) the building.
Second, it's highly absorptive in the IR. Due to the reciprocity laws, this means it's also highly emissive in the IR (and btw it's also N
A minor correction (Score:2)
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Thanks for the correction. I agree that the term "IR" is used for rather a wide range of wavelengths.
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I don't mind when people state clearly that they don't really understand the absorption & radiation equations, but it does kinda piss me off when these same people pontificate as though they did.
We definitely share that hot button. Good analysis.
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If people aren't painting their roofs white and silver today, do they really think their paint will change that?
I would if the Home owner's association police would allow it.
Yes: not all infra-red is the same (Score:2)
The actual article is a bit shallow on detail, but here's my interpolation...
Infra-red is quite a broad bit of the spectrum. It starts at about 800nm as light we can't quite see, and security cameras use this band with an infra-red illuminant. If we go down to about 2000nm, we are into the mid-band where some IR cameras operate. These can see hot objects but cannot people by their radiated body heat. There is a gap at about 3500nm where water vapour absorbs and emits, and cameras do not work well. Then t
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Hafnium in short supply? (Score:3)
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Reserves are defined as the quantity of metal that has been proven to be economically mineable. Generally speaking, if the price of an element goes up, the amount of reserves will also go up, because more more mineralized rock will become ore (ore being rock from which minerals can be extracted at a profit). Another factor that affects reserves and ore are metallurgical processes; a new process which allows for economic seprataion at lower concentrations will have the effect of increasing reserves. So, you
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So, as the price goes up economically viable reserves go up.
Yes. Of course, at some point you'll start getting the material from asteroid mines, because at a few million dollars per kg it's actually worth doing that. Generally, the demand slows as the price increases too though. A roof paint that costs a few thousand times the value of the house probably isn't going to be that popular...
Re:Hafnium in short supply? (Score:4, Informative)
The (paywalled) research paper states: "The use of HfO2 is, however, not essential, and can be replaced with titanium dioxide (TiO2), which is less expensive."
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Probably only about 50% of it can be used effectively...
Re:the law (Score:4, Informative)
Sorry, not possible, as per the first law of thermodynamics.
Nope, quite possible per the first law of thermodynamics, as well as the second and zeroth laws. If the atmosphere is transparent and the object is exposed to the sky, heat can radiate from the object to space (which, even accounting for solar exposure, has a mean effective temperature well below that of air temperature in many places ~ 230K). If the air is still and the object can reflect most of the incident radiation, there is no reason why the object can't cool below air temperature. It is a completely separate mechanism of heat transfer to a different heat sink.
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If the air is in contact with the painted surface (at constant pressure etc.), will the warmer air not transfer its heat, so as to produce an equilibrium of equal temperatures?
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OK. So the original question remains how the temperature of the object can be multiple degrees cooler, in the steady state, than the ambient air. Why would those two heat flows not apprx. balance?
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Re:the law (Score:5, Informative)
-457 farenheit is nothing to sneeze at. (Score:5, Insightful)
What the material is doing (or is claimed to do, anyway) is to re-radiate incident radiation at a wavelength that can pass through through the atmosphere back out to space without being absorbed (i.e. it won't heat up the atmosphere).
More importantly: If the wavelength were one that was absorbed by the atmosphere, it is also one where the atmosphere radiates heat back toward the paint.
If your frequency slot is one with "absorption", you "see" the temperature of the atmosphere - a bit cooler than the surface of the (greenhouse-effect boosted) planet, but not by enough to be exciting.
If your slot is one that is essentially fully transparent, you "see" the cosmic background (except for the tiny part of the sky that shows the sun's or moon's disk). That's about 2.7 degrees K, call it -457 Fahrenheit. Liquid helium is substantially warmer at -452.2.
The slow radiation of heat at the sky is almost completely overwhelmed by conductive and other transfers of heat into the paint, of course. Of the 530ish degrees F difference from room temperature, only nine are left.
But that's nothing to sneeze at. The inside of my well-insulated desert house gets up to about 85 in the day without air conditioning. If I could drop that by nine degrees it would be a relatively comfortable 76. (It would likely actually drop more, because the lower temperature of the surface would slow the heating and tend to even the daily cycle of temperature out further.) 85 or more is debilitating. 76, with drastically low humidity (dew point typically about 35), is actually comfy.
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In the same way that a glass of water with an ice cube in it will be at a lower temperature than the air around it. If the ice cube was essentially infinite (ie like space) then the water will always be at a lower temperature than the air. Energy will flow from the air to the water and from the water to ice cube.
Given that heat transfer is not instant there will always be a temperature differential at each stage.
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Also, this was known and exploited long before we understood thermodynamics:
http://en.wikipedia.org/wiki/R... [wikipedia.org]
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It is possible, because the environment is not in thermal equilibrium. In particular, the film 'sees' colder temperatures at some wavelengths than at others.
Did you not think before you posted that just maybe a bunch of scientists publishing in this area and the reviewers for one of the worlds top scientific journals might possibly have a better understanding of thermodynamics than you do?
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Would you care to be more specific? My explanation is pop-science simplified, but I don't see an error in it.
More detailed explanation:
In the 8-13 micron (wavelength) window, atmospheric transmittance averages about 80% (estimated from a plot in the paper.) So the energy received is about 20% of what you'd get from a black body at atmospheric temperature (plus 80% of what you'd get from space, which is negligible in comparison.) So the brightness temperature at 8-13 microns is lower than ground level atmosp
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"it becomes cooler than the surrounding air by around 9F (5C)"
Sorry, not possible, as per the first law of thermodynamics.
How in the hell do you think dew gets deposited on grass, cars, etc? Dew forms when the surface temperature drops below the dew point of the air, which cannot be any higher than the ambient air temperature.
FWIW, a problem from my engineering heat transfer course indicated that frost can form when the air temp is 9F/5C above freezing.
Too bad ... (Score:2)
According to the report The State of the Global Coatings Industry, the world produced 34 billion liters of paints and coatings in 2012. ...
If we assume paint production has, in recent decades, followed the economy and grown at about 3% per year, that means the total amount of paint produced equals the current yearly production times 34.[6]\((1+\tfrac{1}{0.03})\) That comes out to a little over a trillion liters of paint. At 30 square meters per gallon, "Square meters per gallon" is a pretty obnoxious unit, but I think it's not quite as bad as acre-foot (a foot by a chain by a furlong), which is an actual unit used in technical papers I was trying to read this week. that's enough to cover 9 trillion square meters—about the area of the United States.
So the answer is no; there's not enough paint to cover the Earth's land, and—at this rate—probably won't be enough until the year 2100.
In this house we obey the laws of thermodynamics! (Score:3)
Passively cooling an object below ambient temperature seems... counterintuitive. I think I understand what's going on here, but I'd like to see some more thorough discussion. Particularly, I'd like to know how you can find any passband in which an object at ambient temperature radiates more heat than it takes in from direct solar exposure, except the bands blocked by the atmosphere.
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Direct solar exposure is reflected, then the reflected light and internal heat radiation is modulated to a frequency that passes easily through the atmosphere. I'd have to question the efficiency of modulation, which seems to be where their breakthrough occurred.
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This "modulation" happens all the time, few things in this universe are true blackbodies, most prefer to radiate in specific bands. They're apparently using a material that tends to radiate only on one narrow band at regular earth temperatures.
Not sure how much benefit this provides to the building owner, to the point that they'd be willing to cover their building in hafnium-and-silver coated panels, rather than just white paint...
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White paint only reflects light, and inhibits radiative cooling since radiation follows the same curve as absorption. This surface might actually be *less* effective than a good roof-white* paint at reflecting incoming sunlight. But if you've ever been in the desert and noticed how rapidly it cools at night you've gotten a little taste of what a dramatic effect radiating into the near absolute zero blackness of space can have. There they accomplish it by having extremely low water levels in the local atm
Re:In this house we obey the laws of thermodynamic (Score:5, Informative)
"Ambient" is important to define here. The temperature of the air is not actually playing much of a role in the black body equation. If the sky was made of more buildings at ambient temperature, then the story would be different, but other than the sun it's mostly an open pit into which anything radiated never returns. Also keep in mind that that figure may be referencing the temperature of the air near the whole building including the lower floors; it is cooler up high on tall buildings.
The idea is that the heat provided from within the building and the heat from the 3% of sunlight that gets through the mirror all pools and the mirror material then converts it to a specific passband. So you have more heat pooling than what comes in on that passband.
How effective this system remains when contaminated with a coat of dust is a question. Also comparative advantage to absorbing the heat/light and using it to power AC.
if you can see the color of the paint... (Score:1)
A light covering of dust tha
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It's not the ambient temperature of air that's key here, it's the ambient temperature of space, which is about 2,7K.
All objects are constantly radiating energy and receiving energy back from other things that are radiating. When two objects in radiative exchange are roughly the same temperature, this balances out. But when one is hotter than the other, the hotter one loses more energy than it takes in, and vice versa. And it's not just a little difference - radiative heat loss is proportional to the absolut
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Refect instead of radiate (Score:2)
This painting reflects infrared instead of radiating it, but does it change anything to global warming? If there is too much CO2 in the atmosphere, the heat is trapped, does reflecting instead of radiating changes the game?
Or is it just about making sure visible light is not turned into infrared by radiation?
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Actually the primary greenhouse gas is water, but water only absorbs a certain frequency-band of infrared radiation. CO2 then absorbs another adjacent frequency band, and between them they cover most of the frequency band at which things at earth-normal temperatures generally radiate thermal energy, thus trapping the heat by re-radiating (it's not really reflection) a large portion of the absorbed heat back down to the surface.
This surface though gets tricky - it has apparently been designed to radiate hea
I saw this movie. (Score:1)
It sucked. Why did they have to be on a train? That didn't make any sense at all.
Some details from the paper (Score:5, Informative)
For those fortunate enough to have institutional access, the research paper is here [nature.com].
Quickly picking some highlights:
The atmospheric transmission window is between 8 and 13 microns. They achieved 4.9C below ambient in direct sunlight at 850 watts per square metre. Cooling power was 40.1 watts per square metre. Emissivity (equivalently absorptivity) averages about 70% in the 8-13 micron window (estimated from a plot.)
Here's a quick back-of-the-envelope calculation
90% reflective white paint: absorbs 85W/m^2
97% reflective foil: absorbs 25.5W/m^2, an improvement over white paint of ~60W/m^2
This film: emits 40W/m^2, an improvement over simple foil of ~60W/m^2.
So in this scenario, the special film gives twice the benefit compared to just going for something simple and reflective. (The 90% for white paint is guess-work. The 97% for 'foil' is just matching the special film. Perhaps someone can update the calculations with better founded values.)
The summary title is highly misleading.
It is not paint, it is a manufactured film. It cools buildings, not planets. Yes, with enough you could cool the planet, but if you wanted to take that route, it would be much more cost effective to just use aluminium foil and use a marginally larger area of it (or, indeed, white paint.) Back in the real world, the way this invention cools the planet is by reducing electricity demand for air conditioning. (I saw another article about this in which one of the authors makes exactly this point.)
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Not really - the 40Wm^2 of cooling is only useful if it is in contact with something that can move that cold to where it is needed. (Hand-wavy explanation, really we are shifting heat to the film.) It also needs to see mostly sky, which windows usually don't.
You'd put it on your roof and run water behind it to shift the heat around.
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I think the second photograph in the article is the researchers reflected in their piece of film, so the answer is it is reflective like a mirror. I imagine you could put some translucent layer over it at the cost of some efficiency.
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Emissivity and absorptivity are the same thing. One way to look at this is the time-reversibility of physics on a microscopic scale, another is that something that was really absorptive but not emissive or vice-versa would give you a really easy way to beat the 2nd law of thermodynamics. Emissivity can, however, vary with wavelength, which is the trick here.
Better to use the energy? (Score:1)
Use on Venus? (Score:1)
Could this stuff, or something related, help us reduce temperatures on Venus? http://en.wikipedia.org/wiki/Terraforming_of_Venus/ [wikipedia.org]
We drink our rain water around here (Score:1)
Ooh! (Score:2)
Hey scientists (Score:1)
...drop everything you’re doing RIGHT NOW and come here to Siberia. 32C today, 27 this weekend.
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Also, Slashdot, get real and learn not to lose Unicode.
-32 (resp. -27) degrees Centigrade.
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Reply (Score:1)
Radiative cooling substance (Score:2)
There is a cheaper alternative. Coat the surface with small crystals of oxidane. Its very good at reflecting heat. In large quantities it is very good at absorbing heat..
I have a driveway full that you can have for free, just bring your own shovel.
How much energy does the making consume? (Score:2)
That's all I've got.
The other way (Score:2)
Isn't this the story of SnowPiercer? (Score:1)
So what's better... (Score:2)
This is just silly (Score:1)
Wood stove? (Score:2)
I wonder if one could paint this on a wood stove to increase the heart output.
Re: Happy Thursday from The Golden Girls (Score:1)
The Global Warming Scare is now over! Thanks paint!
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Unfortunately, it will also kill your dog and blind your children [the wavelength is just right for killing eyeball cells as they develop].
And it tastes bad. Paste is WAY better.
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Been there, done that. [cnn.com]
Re: Sherwin Williams (Score:2)
They can use the old Sherwin Williams slogan: "Cover the World!"
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http://newsroom.melbourne.edu/... [melbourne.edu]
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I do not own enough ground to plant 10 trees per year.
Unless you are proposing cutting all the forests to get free land which can be given to people so they can plan 10 trees per year.
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Fair call :-) I have no room either, I get a non-profit to plant a few trees on reclaimed land for me every year. Surely governments can afford some seedlings to plant in place of deforested areas to absorb carbon etc. If they could coordinate to plant 10 trees per human per year, surely it would help somewhere along the line.
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This is non-trivial amount of land. I'm not sure how much space tree needs to grow properly - let's assume 10m^2. In my country, we have around 40mil people. 10 trees per year per person is 40.000.000 * 100m^2, which is 4.000.000.000m^2, which gives 4000km^2. Each year.
Entire land area of country is around 300.000km^2. 30% of it is already forest. 60% is agricultural land.
What you are suggesting is planting 1.3% more area of forests each year. In 50 years, there would be no agriculture anymore - just 90% fo
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"Just starve all people out by destroying all agriculture lands in one big go, planet will heal itself. Not that there will be anybody to care."
I suspect the planet may have reached that point already, but then we get into the sticky matter of population control. A topic that from experience gets ugly pretty quickly.
Personally I think we're all screwed and CO2 is only single link in a chain of serious issues. Environmental contamination with heavy metals, particulate matter, plastics etc etc are things tha
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That'll be the Walkie Talkie building
http://www.bbc.co.uk/news/uk-e... [bbc.co.uk]
The problem isn't reflectiveness alone, the shape of the building played a part too.