My human civilization is facing (much like us) the threat of anthropogenic climate change. For whatever reasons, they are unwilling to take action by reducing the use of fossil fuels and refuse to use "normal" geoengineering.

Ultimately, they decide for a rather unusual (and stupid) solution: air-conditioning

Pretty straightforward eh! If the atmosphere is too hot just cool it down. Obviously the consequences on the climate would be dire to say the least. However, I am not interested in that. What I'm asking is:

Do we have the technology to build an "air-conditioner" (the scale is not important, a single gargantuan one or a billion tiny ones I'm not interested) that can cool the atmosphere, such that the waste heat is in the form of infrared photons that are (mostly) radiated into space? (So that we have a net cooling of the planet as a system)

Limitations: It can use only current technology and must be powered by electricity.

EDIT: It seems many are confused about this question. All I'm asking is if we can build a machine that cools the air and radiate the waste heat in outer space.

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    Does it have to be infra-red emission? After all greenhouse makes that more difficult and you'd end in a vicious cycle of more heat -> more emission -> more greenhouse -> more heat – ArtificialSoul Sep 13 at 13:09
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    Depends on how far you are willing to loosen the definition of air-conditioner: The greenhouse effect may be dubbed a reverse air-conditioner, and thus any technology designed to bring up the amount of infrared radiated into space, or more specifically, the parts of the atmosphere then engineered to radiate more, may be eligible for the monicker 'air-conditioner' - but then the borders between terraforming and building of an airconditioner would be blurred to the extreme. – bukwyrm Sep 13 at 13:41
  • @ArtificialSoul I don't care about infrared, I just want to cool the atmosphere directly with work, so the waste heat must go into space, I don't care how! – SilverCookies Sep 14 at 7:56

Not possible

enter image description here

Earth's energy budget is such that there is an estimate +0.58 W/m$^2$ energy flux, averaged over the Earth's surface. For a surface of $5.1\times10^{14} \text{ m}^2$, this means we have to push about 300 TW back into space.

Total human energy consumption from all sources is about 18 TW. Global primary net productivity is around 70 TW. Therefore, all humanity, and all plants and algae on the planet, capture about 1/3 of the energy that we need to direct back into space.

The sun hits the Earth with 174,000 TW of solar power, so it is kind of overwhelming. Current technology can't solve the global warming problem by direct energy transfer.

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    +1 for the numbers showing the magnitude of the problem. We can absolutely pave Africa and Central Asia with reflective tinfoil. Nobody lives there anyway. (For suitably chosen meanings of "nobody"). We can place lots and lots of mirrors in orbit. We can spread a planet-wide aerosol cloud in the stratosphere. And if (or maybe, when) the climate will really take a bad turn we will most certainly do it. – AlexP Sep 13 at 13:37
  • Mirrors in orbit or a sunshade at the Earth-Sun L1 point are about the only conceivable ways to reduce insolation with current technology. – Thucydides Sep 14 at 4:14
  • very interesting point, but not the answer I was looking for. I am simply asking for technological capabilities – SilverCookies Sep 14 at 7:52
  • @SilverCookies My answer is that you can't do this. We need to capture 300 TW and beam them into space with your air conditioning machines, but all of humanity only generates 18 TW. So, no matter what the design of your machine, there isn't enough power to make it work. – kingledion Sep 14 at 12:04

Completely possible

Fly your trusty Giant Ice Cube spaceship to comet, cut out a giant block ice, fly it back to Earth and drop it in the ocean. Repeat every few years until the comet is empty, then panic and destroy all robots.

enter image description here

(If it works for Futurama, it'll work for you!)

Build a shade. No, build many shades.

Weather baloons are cheap, so are the space blankets in a first aid kit. Attach 4 baloons to the corners of a big blanket, add a frame to keep the blanket unfolded and let the construct soar into the sky. Just make sure you have the cooling side of the blanket facing down...

Weather baloons usually rise until they pop in the thin atmosphere, so you need to anchor your sun shades above cloud level somehow. A thin wire back down to earth might work, or you attach a little water tank and a controller to the bottom (parachute style). The controller measures the current altitude and releases water if the baloon sinks too low due to gas escaping.

And if you insist on using more energy than the controller needs to measure altitude and release water, you can replace the weather baloons with drones. These would have to have big rotors (they would resemble a helicopter or military drone more than a quadcoper drone) to even be able to reach the required altitude and use up far more energy.

Sure thing! (as long as you remove the need for it to be powered)...

Stanford researchers have developed a composite which does exactly what you need, with the bonus of not requiring power and therefore pumping more heat in to your environment. Don't forget, every watt of power you consume is a the same amount of heat created.

Cover as much of the earth's surface with this as possible and you'll see some pretty severe temperature swings. It works in two ways, by reflecting 97% the incoming solar energy back in to the atmosphere, and emitting heat in long infrared to minimize interaction with the atmosphere.

And if you REALLY need them to require electricity, then I can install a green flashing LED on them to let you know everything is working fine.


This is a computer heat sink:

CPU hest dink

It is built out of metal, and to maximize its surface-to-volume ratio.

You need is continental arrays of these beasts in temperate areas, and in such a way that they get the least solar exposition possible. They should also be sealed within glass with a vacuum inside. By night they will pull heat from the ground and radiate it to space. You may have to move the population of North America, Europe and Russia to the tropics in order to cover enough area for this to work, but hey, what is a little eviction between friends?

  • A computer heatsink is designed to maximize contact-based thermal transfer between the fins and the atmosphere. There's no atmosphere in space, so instead you need to transfer heat by radiation. A heatsink is worse than useless for that: not only does most of the radiation from the fins get re-captured by other fins, but radiative efficiency increases dramatically with temperature, while the increased surface area of the fins moves things the other way, reducing the temperature. – Mark Sep 13 at 22:01
  • I agree. The reason for the ventilator is convection: So to get rid of heat you need air. Heat Sinks do not radiate away their heat. The transfer is CPU -> Metal body (through thermal conduction). Then metal body -> surrounding air (through convection). – ArtificialSoul Sep 14 at 8:37

The greenhouse effect is what keeps this earth from being a snowball, without it, global mean temperature would be -17°C - it is just the tiniest amount out of whack - about 2.7W/m2, meaning two and a half Watts per square meter too much power is retained, slowly heating the earth. ( So to just cancel it, we'd need to get that down to zero. To actually cool down, we'd need to go beyond that. Heat pumps are about 300% effective, meaning for every Watt invested you heat as much as you would using resistive heating of three Watts. Same applies to cooling. So to get -3W of effect, we need to invest 1W into a heat pump. For every square meter. This should work solar powered, because otherwise the energy-production will free even more energy (it might bite us in the rear with solar modules, too, because they absorb a lot of the light to heat - we'd need special modules that have a high albedo). So we'd need 1W/m2 of solar capacity, on the whole earth, or, assuming 20% efficiency on the solar panels, 250W/m2 light (already including nightime) - solar cells on 1/50th of global surface, which is just double the surface of North America.

The direct way of increasing albedo by covering some landmass in mirrors would be hugely more effective, but no airconditioning per se (if you're not inclined to redub earth 'airconditioner'...)

  • Heat pumps have to pump the heat somewhere. Where would you put the part of the circuit that heats up? – Elmy Sep 13 at 14:26
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    Into the ocean for rather quick karma, or as infrared above the clouds. Both are bonkers, but on different levels. OP wanted an airconditioner, which is a heat pump, so i went for it. – bukwyrm Sep 13 at 14:39

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