One recurring theme in science fiction is that after mankind taps some practically free source of energy (like nuclear fussion), the planet is in danger of overheating due to excess use of energy.
What would be some ways of dumping Earth’s thermal energy? Since we now have all that free energy, dumping heat wouldn’t be too hard, would it?
IT IS? CITE?
Conduction? Wont work. Nothing to conduct it through/with.
Convection? Wont work. No medium to carry it away from earth.
That leaves radiation to space, the only game in town is left, and it does work.
What "Free Energy?
Have you been frequenting the free-energy nut case sites?
An admirer of Tom Bearden, A proponent of the “Joe Cell.”
Let me sell you a tinfoil hat!
Well conduction can work, you can heat a object then shoot that object into space.
I think the OP was being hypothetical.
I’ve seen excess heat mentioned as a Bad Thing in a number of SF stories. ISTR that the heavily-urbanised puppeteer homeworld in Niven’s Known Space series suffered from it before it was launched into interstellar space as part of the Fleet of Worlds. Afterwards, the excess heat just kept the place toasty-warm. (The accompanying worlds needed artificial suns to provide their energy and sunlight.)
In my opinion, there’s nothing particularly whacko about the idea of excess heat worldwide being a problem, once you assume a sufficiently-large flow of incoming energy. The overall temperature of the surface of the earth is affected by the rate at which energy leaves it, and the rate at which energy enters it.
Ideally there’s a balance between the rate of energy leaving and the rate of energy entering. If suddenly less energy can leave the earth at a given temperature, the earth will warm up until the rates balance again. Likewise if more energy enters the earth (such as from some new human source of energy. )
Global warming is a problem because the rate at which energy leaves the earth at a given temperature is decreasing. Changes in atmospheric composition are reducing transparency to emitted infrared radiation, and thus the equilibrium temperature of the atmosphere must increase until the outbound radiation balances the incoming energy again.
That could be considered very solid radiation. 
Free energy? Grab some nearby resource rich moons, form a Klemperer rosette, and abandon the sun. No problemo!
A heated-earth situation is mentioned in Arthur Clarke’s 3001: The Final Odyssey. There are other SF works but I can’t recall any titles.
Sorry, I was speaking hypothetically. Please read my last sentence as: “If we had all that free energy, dumping heat wouldn’t be too hard, would it?”
Assuming 1kW of solar energy per square meter and an aspect area of 1.3x10[sup]14[/sup] m[sup]2[/sup], we would have to be generating in the millions of terajoules of waste heat per second to even be on the same order of magnitude that the Earth normally sheds. By the time we can produce sufficient energy to waste that much heat, we’ll be able to build big equatorial radiators extending to space, or better yet, build orbital habitats and turn the planet into a giant nature perserve. It’s not high on my list of things to be worried about.
Stranger
We could strongly influence the strength of Earth’s radiation by altering its emissivity. Reducing atmospheric CO2 would help. Also, we could make Earth appear lighter in color to reduce the solar radiation that we convert to heat.
We could deploy a solar shade in orbit to block some of the sunlight.
Heat pumps powering high power lasers - pref x-ray to prevent atmospheric absorption (cf Sundiver by David Brin, albeit on a much larger scale).
probably need to be located at the pole pointing along the axis of rotation.
Has the added advantage of being able to be used to drive a solar sail starship to the pole star 
Si
If we’re going to do that, it would be nice to put them to some kind of use, perhaps modulating the transmission to transmit information toward hopeful extraterrestrial SETI projects, at least.
Set up ground-based lasers to shoot the myriad tiny objects in LEO; they’re a hazard to navigation anyway. Perhaps not as much as ground-based lasers that can vaporize something in orbit, but what are ya gonna do?
Invent matter replicators which consume a huge amount of energy. With the planet supporting billions of people, that should soak up a fair amount of the excess energy, giving everybody their own flying car and metallic jumpsuit.
You could get ice from a comet and drop it into the ocean.
I’m not sure about the laser idea - for it to act as a radiator, wouldn’t you need to use the ambient heat to power the beam? And to do that, you need a temperature gradient, which means you need to bring “cold” from outside the earth by some other means.
Seriously, the most practical ways to cool the earth are to (1) increase the IR radiation, e.g. by reducing atmospheric CO2, and (2) decrease heat input, e.g. with a sun shade.
I think it would be quite hot by the time you got it to sea level.
There are usable temperature gradients here on Earth; if you use these to generate energy and dump that energy out into space as X Rays, then the net heat on earth is reduced (the remaining heat is also less organised)
You just have to bring it down gently, preferably in a spaceship.
(Although that was supposed to be a Futurama reference and not a serious suggestion. Not that it wouldn’t work, but it’s probably not the most efficient method.)
OK, that’s true. But by the time we need to consider such drastic means for cooling the earth, there may not be any big sources “cold” left on the earth. Also, if there were any left, it would be more efficient to use the gradient to generate electricity and feed it into the power grid, thus reducing the amount of energy that needs to be generated by fusion.
[post=7804833]Difficult, but conceptually feasible[/post].
Yeah, you’re adding all that kinetic energy. The negative thermal energy of the ice in the comet is a nonce in comparison.
I don’t think you could get an overunity coherent output directly from any hypothetical medium from a distributed “heat” energy source, particularly one with the small thermal differences you find on Earth, and any staged process using a mechanical heat engine or conventional solid state heat transducer is going to have so many inefficiences that’s it’s probably not worth it. And you’d have to figure out some way to “pump” heat from the environment into the medium, which itself would result in net heat production. (Unless we posit Maxwell’s Daemon, stopping the slow moving atoms from entering and only allowing the fast ones, which if course is thermodynamically impossible.) Plus, that would have to be one gignormous lasing cavity for a high energy infrared laser.
You might be able to bind up some of that heat energy into gravitational or chemical potential energy, but I don’t think there’s much you can do from a conventional standpoint that will increase the Earth’s natural thermal balance to a negative. (Making it retain additional heat seems to be somewhat easier, but that’s obviously not our goal.) So, move your heat polluting industries off-planet, 'kay?
Stranger
It’s not just the friction; it’s the dissipation of all that potentisal energy too - for the same reason that the ‘vapour canopy’ hypothesis put forward by some Biblical literalists wouldn’t work.
There’s nothing thermodynamically impossible about the idea; it might be horribly inefficient and pitifully ineffective, but you can extract energy from thermal gradients (at the expense of flattening them), and that energy can be made to leave the system, at least in theory.
The only way the planet is going to have a net loss of energy is by radiation, non? And (assuming otherwise unalterable graybody properties) radiative emissivity is essentially a function of temperature difference so far as the Earth is concerned. So, in order to get a steeper heat transfer gradient, you are going to have to have to create a high temperature reservoir in what is otherwise a closed system. Pumping heat from a low thermal state to a higher thermal state results in net energy “waste”, i.e. more entropy and net enthalpy loss, thus any system that involves increasing the temperature to make a process thermodymically efficient is going to be a losing game in the end. The only way you can make this work is to create a refrigeration cycle that uses an extraterrestrial low temperature reservoir, which is what you’re trying to accomplish in the first place. In other words, the Earth is already has a maximum throughput for radiative thermal balance, and that’s as good as it’s going to get without creating a thermal conduit that is more conductive and (at its terminus) radiative than the atmosphere. Only Maxwell’s Demon can violate the 2nd Law of Thermodynamics, and like Schrödinger’s simultaneously alive and dead cat, he doesn’t exist in the real world.
Stranger