# Global warming - why doesn´t mankind collect heat (thermal energy) and turn it into electricity or send it to space?

Why doesnt mankind "collect" thermal energy (there has to be some way: thermal couplings, detour over chemical energy, whatever) and after it has been concentrated at one point, turn it to electrical energy (like steam turbines do) or at least radiate it to space?

• Heat exchangers can be purchased for home use, working like refrigerators in reverse in the winter for heating, and not in reverse for cooling in the summer. There are solar farms where sunlight is redirected at a heat exchanger to make steam for electricity generation. Why would one send energy out into space (besides TV and radio doing that all the time)? – CrossRoads Jan 9 at 16:42
• @CrossRoads to at least get rid of it - solving global warming - if its not possible to use it. If so - even better! Do heat exchangers maybe need more energy than they can create by bundling heat and sending it to a turbine i.e.? – Martin Eckleben Jan 9 at 17:09
• Re: "dumbest thing ever asked", no, there are plenty of dumber things that have been asked. And even if there were not, as you imply, everything that everyone ever learned was learned on some day in their life. Today is your day for this question. Re: "there has to be some way" -- Science already knows how to solve global warming. There is a way. What there is not is a way to solve the problem without massively changing energy policy. Governments lack the will to implement even the first baby steps of a solution. Unfortunately the victims of this inaction will be your generation. – Eric Lippert Jan 10 at 1:02
• @EricLippert Well, there are things that can be done to cool the global environment certainly. We just have to make sure whatever cure or combination of cures is chosen: That the cure is not worse than the disease. Going off the oil cold turkey is guaranteed to cause more problems than it solves... – Stian Yttervik Jan 10 at 10:41
• There's a difference between "stupid" and "ignorant". "Stupid" either can't or won't learn anything, but ignorance is simply a lack of information. Asking this question admits ignorance, not stupidity, since you are trying to get more information to curb your ignorance. And everyone is ignorant about something, since no one knows everything. – computercarguy Jan 10 at 19:27

Collecting thermal energy is really hard. As others have said, things like heat pumps exist for moving heat around, but the laws of thermodynamics (which are fairly fundemantal in physics) require that moving heat around will always generate more heat.

Now, the amount of extra heat generated can be less than the amount of heat that's being moved - so if we had a way to build a heat pump that moved heat out of the earth system and into space, then it might be worthwhile. There are three problems with that,

1. We don't know how to do that. A system of pipes going into orbit probably isn't practical!

2. Having got the heat into orbit, getting it away from the equipment and into space is hard. You've probably learned about heat moving by conduction, convection, and radiation? The first two are not available in space, because there's no material to conduct into and no atmosphere to convect. So radiation is all that's left. On top of the hypothetical heat pump to orbit, we'd need a massive radiator system in orbit as well.

3. The scale at which it would have to be done is gigantic. Even if we knew how to do it, we might not be able to do it.

So it probably isn't theoretically impossible - at least so far as we know - but it's not something that's possible at the moment.

It's also worth noting that like all ideas that are about getting rid of heat rather than reducing the greenhouse effect, it doesn't actually solve the problem - it just mitigates the symptom. If we carried on emitting greenhouse gases while using this system then we'd have to keep using this system, more and more, for ever.

(theoreticians: am I missing something? Is there actually a theoretical, rather than practical, blocker here?)

• Thank you for the explanation it made a lot clearer and I agree on every point made. I actually thought (very shortly :) ) about every point you made before I asked. Just for the lulz: for 2. I thought about heating stone to magma with as hot as one can heat it and then discarding it to space - but immediately threw the idea as sending millions of tons of stone to space as payload is probably the heart attack of every space project financial officer :D – Martin Eckleben Jan 10 at 15:18
• @Martin Eckleben The SpaceX BFR is projected to lift 150 tons of payload into low Earth orbit. Let's assume all of the energy of the magma is radiated into space (some will be reabsorbed by Earth). 150 tons of rock near its melting point (1200°C) has ~90 gigajoules of thermal energy. Incident solar energy on the Earth is ~180,000,000 gigajoules each second! Your hot-rock rocket would be a drop of water in a rainstorm. Removing CO2 from the atmosphere, or not adding it in the first place, reduces heating over many decades by altering the amount of solar energy trapped by the Earth. – WaterMolecule Jan 10 at 17:03
• WRT radiating heat to space, it might be instructive to look at the cooling system for the ISS: en.wikipedia.org/wiki/External_Active_Thermal_Control_System Not exactly a small project, and that's for 3-6 people and equipment, with no fossil fuel burning involved. And a mostly white habitat module, so it probably doesn't absorb much solar radiation. – jamesqf Jan 10 at 20:20
• @MartinEckleben: you would do well to start habitually computing orders of magnitude as in WaterMolecule's example; this is a valuable skill that many middle school students, and indeed many adults lack. People are not accustomed to thinking about heat on a planetary scale. The amount of sunlight falling on a single square meter of land at the equator at noon is an energy equivalent of 14 hundred watt light bulbs. Multiply that by all the square meters being illuminated, and that is rather a lot. – Eric Lippert Jan 10 at 20:38
• Futurama (theinfosphere.org/Transcript:Crimes_of_the_Hot) covered this scenario: "Fortunately, our handsomest politicians came up with a cheap, last-minute way to combat global warming. Ever since 2063 we simply drop a giant ice cube into the ocean every now and then...Of course, since the greenhouse gases are still building up, it takes more and more ice each time. Thus solving the problem once and for all." :) – CCJ Jan 10 at 22:53

Your middle school physics perhaps hasn't gotten to thermodynamics yet. The three laws of which can be summarized as 1) You can't win; 2) You can't even break even; 3) You can't leave the game.

The crucial point here is that heat engines don't actually work on heat, they work on temperature differences. So you can't really "collect" heat and turn it into other forms of energy, because you need a colder place to transfer the heat to in order to convert the heat to say electricity. Which is why power plants are usually situated by oceans, lakes, or rivers, in order to use the water as the cold side of the generator. (And ones that aren't have large cooling towers, in order to use the air.)

When you do move heat around, say with the heat pumps used for home heating and cooling, you're always using some extra energy to "pump" the heat from one place or another. If you're heating, you move some heat from the ground outside to your house, but the net result is that the system of ground+house gets a bit warmer, because the electricity used for the pump becomes heat.

WRT sending the heat back into space, that's actually the cause of global warming. Atmospheric CO2 acts as an insulating blanket, preventing some of the sun's heat from being radiated back out into space. By increasing the amount of CO2 in the atmosphere, we've increased the thickness of the blanket, so the Earth gets warmer.

• For answer to your comment, see below. – Michael Walsby Jan 9 at 19:24
• @MartinEckleben: The good news is: we have a device which extracts CO2 from the atmosphere, and another which combines it with hydrogen to form synthetic fuel. The bad news is that it costs around $600 per ton of CO2 processed, which is orders of magnitude more expensive than planting a few hundred trees. See technologyreview.com/s/612928/… – Eric Lippert Jan 10 at 1:11 • @Martin Eckleben: Chemical reactions are subject to the same thermodynamic laws. (It's just more complicated to explain.) Endothermic chemical reactions have to be driven by some energy source. They might, as with photosynthesis using sunlight to turn CO2 & H2O into hydrocarbons & carbohydrates, store energy in the end products of the reaction. But when you go to extract that energy, say by burning firewood, you never get back 100% of the energy that went in. – jamesqf Jan 10 at 5:18 • @EricLipper Well, yeah, the main problem is that there's just so incredibly tiny amounts CO2 in the atmosphere to begin with. Trees suck at it too (other plants do much better), but they mostly reproduce on their own. There have been other proposals, like fitting vast algae tanks to e.g. coal power plants that consume the carbon dioxide emitted from the plant and sunlight, and produce fuel. Of course, taken as a whole this is far less efficient than something like a concentrated solar power, but at least it can be reasonably well fitted to existing plants and doesn't need continuous sunlight. – Luaan Jan 10 at 8:00 • @EricLippert When you said that we have a device which extracts CO2 from the atmosphere and makes fuel with it, my first thought is that the device you were referring to was a tree. - haha – reirab Jan 10 at 9:00 The new materials reflect a broad spectrum of light, in much the same way as mirrors or white paint do. In the crucial 8–13-µm part of the infrared spectrum, however, they strongly absorb and then emit radiation. When the materials point at the sky, the infrared rays can pass straight through the atmosphere and into space. That effectively links the materials to an inexhaustible heat sink, into which they can keep dumping heat without it coming back. As a result, they can radiate away enough heat to consistently stay a few degrees cooler than surrounding air; research suggests that temperature differences could exceed 10°C in hot, dry places. • That pretty neatly avoids the absorption due to carbon dioxide, too. Though I suspect that even with a concentrated effort, you'll never get anywhere close to the amount of radiation needed for any appreciable global cooling, not to mention the likely disruption of the weather patterns if you could. :P – Luaan Jan 10 at 8:04 • Key to this is that the sun is small in the sky, while the radiators emit over a hemisphere. The absolute heat flux is rather small, so they're mainly proposed for keeping solar panels cool (efficiency drops with increasing temperature) or to reduce the power consumption of refrigeration and air conditioning, i.e. very much local. It would be interesting to model whether this can be scaled up to the city level, to reduce urban heat island effects (also @Luaan) – Chris H Jan 10 at 8:38 • @ChrisH given that many urban areas don't even make use of the low hanging fruit which is trees, I don't see wide scale adoption of construction standards utilizing this material any time soon. – Turksarama Jan 10 at 14:05 • @Turksarama of course you're right, but passive radiators can go on rooftops (of course so could solar panels, and adoption of those is pretty poor too). – Chris H Jan 10 at 15:13 • I fail to see how a panel which is cooler than the environment will help cool the planet by radiating more than its surroundings into space. The opposite is needed: One which is hotter because one has concentrated dispersed heat in it, by which means ever. – Peter - Reinstate Monica Jan 12 at 21:31 As others have pointed out, if you use the energy, it turns right back into heat. Radiating it back to space is at least theoretically possible. But there is a problem with scale. The Earth receives about a 100 petawatts of energy from the sun. And it radiates almost exactly the same amount back out. Everything humanity do with energy is about 0.02 petawatts. Even if we radiated all that energy into space it still wouldn't matter much. Still, it is barely possible to do something like this, by bouncing the sun's light off the Earth surface as it arrives. While mirrors would be ideal for this job, they are expensive. Fortunately, any really bright white object does almost as good a job. Look up Albedo for more information. It would take a very large area of land to make any difference. And land is expensive. And we would need a lot of white stuff to do the job. Even if it is cheap by the square meter (sq feet), it will be expensive by the million square kilometer (million sq mile). So, this is on the list of things we could do if we only found the money for it. • This! The equilibrum you mention in your third paragraph will always hold - what we suffer from is that the the state of our athmosphere controls to what (ground) temperatures the radiation equilibrum corresponds. Adding greenhouse gases leverages a lot more temperature change than any "industrial" form of active radiation can counter – Hagen von Eitzen Jan 10 at 20:59 • There is a severe misconception here: reflective surfaces do not cool via albedo. It is too late to rise albedo once solar radiation has reached the ground. It is trapped, mirror or not. They can help reducing energy consumption of air conditioning and avoid the heat island effect of urban areas (unproven). But better use the area for solar panels (or green roofs) than mirrors or white paint. – user18607 Jan 11 at 21:19 • @EricDuminil (I compressed my reamrks) This is how greehouse gases work: en.wikipedia.org/wiki/Greenhouse_gas. For albedo to be effective (like in ice ages and ignoring other conditions), atmopsheric greenhouse gases must be low. You can't paint a continent white or cover it with mirrors. Covering all roofs with reflected surfaces would lower energy demand in hot areas, but could raise the overall atmopsheric temperature and have the contrary effect. web.stanford.edu/group/efmh/jacobson/Articles/Others/…. Albedo alone is not a cure, in our case of global warming. – user18607 Jan 12 at 20:54 • @ebv: I give up. At least one thing you wrote is correct : "there is a severe misconception here". – Eric Duminil Jan 12 at 21:05 • @EricDuminil: sorry, maybe i should have written "does not cool the atmosphere but prevent heating of the ground directly underneath". Unfortinately, there is more to it than just raising albedo, radiation must be able to esacpe to space. Peace :-) – user18607 Jan 12 at 21:18 Just to hammer it down: the amount of energy transferred to Earth by the sun every single day is colossal. In comparison, the heat generated by all human activities is negligible. For instance, burning every single tree on Earth would release less than 1% of the heat the sun sends our way every day! Taking human activities as an intuitive reference point is utterly misleading. Heat exchanges in the atmosphere involve massive amounts of energy that are far beyond anything human industrial capabilities can handle. Greenhouse gases act like a kind of space blanket: a very thin and light insulating layer that can still trap quite a lot of heat. Though the excess of gases we release only capture a tiny extra fraction of it (well below 1%), the energy the sun sends our way is so tremendous that this little extra heat is enough to mess up our climate badly. Our problem is not to make any use of this extra solar energy. We could move around a minute fraction of it to our advantage (for instance concentrating it inside a house in winter and pumping it out in summer), but as a global system our habitat (the surface of the Earth and a bit of breathable atmosphere above) is receiving far, far too much heat, on a scale that dwarves all human uses of energy. Our problem is to get rid of it, that means sending it some place where it can't wreak havoc with our climate. At this scale, that leaves only outer space or deep soil as potential dumps. So far our atmosphere did quite a nice job of sending solar energy back into space, but we fouled it up. What a bummer... We sure could think of just moving all that heat out of the way ourselves. But alas, as the 2nd law of thermodynamics and its dreaded entropy states, any kind of mechanical work requires additional energy and generates more heat. Even a refrigerator adds more heat into the environment than it pumps out of its internal compartment. All we can hope to achieve is transfer heat from place to place. At the cost of more energy, raw materials, time, industrial capacity and, naturally, money. That is dictated by fundamental laws of physics that no amount of wishful thinking can sway. Painting deserts white or drilling deep underground geothermal wells or putting fancy space radiators into orbit are just sci-fi fantasies. We simply don't even come close to having the energy, materials and technology to implement any of these on a scale that would solve the problem. Picture yourself being wrapped in a space blanket, getting a bit too hot for comfort. Trying to move the hot air away from your body will only make you warmer, while removing the blanket might cool you down fast, with a lot less efforts. Indeed, the only thing we could hope to act upon is the blanket itself. Wisdom would dictate to start by not making it any thicker. Stop burning fossil fuels and breeding farting cattle for a couple of centuries, waiting for all the junk we spewed so far to dissipate. There is also the crackpot scientist alternative: spewing more junk (like sulphur) into the atmosphere to try and mitigate the greenhouse effect. Frankly I hope I'll be dead before I see the idiots try. • Yeah, humor is the best way to stomach this thread. sigh – user18607 Jan 11 at 21:22 • We're in for a rough ride, but maybe we can still strive to go down with style? – kuroi neko Jan 11 at 21:57 • Excellent and completely correct answer. Well done. – Eric Duminil Jan 12 at 16:52 • @EricDuminil Correct except for the disdain towards geo-engineering. We are geo-engineering already and should better get it right real soon. – Peter - Reinstate Monica Jan 12 at 21:36 • Also, I don't think the answer is correct. 1. "All we can hope to achieve is transfer heat from place to place." This is exactly what the OP suggests, yet you seem to dismiss it. (2) "Even a refrigerator adds more heat into the environment than it pumps out of its internal compartment." Well, if the environment is space this is again exactly the OP's suggestion. We couldn't care less how much we radiate out as long as we cool our planet. Earth is by no means a closed system, and the OP proposes to exploit that fact. – Peter - Reinstate Monica Jan 12 at 22:25 Your idea: concentrating the heat, using the energy for something useful and then dissipating it into space could actually be accomplished by a space mirror. There is a special orbit called L1 that's in between the Earth and the Sun and is just the right distance so that something in that orbit will track and orbit in sync with the Earth. It could both shade the Earth a bit and be a massive power plant. You might check out this article from live science on space mirrors. It goes over the pros and cons of this idea. Wikipedia also has an entry on this idea. • Hmm even this orbit is probably full of junk? Also gathering and sending up an amount of materials as needed for such a giant space mirror would probably not work due to scale? But very interesting idea :) – Martin Eckleben Jan 11 at 9:55 • No, Earth-Sun L1 is not full of junk yet. But the mirror or whatever shady device or devices one puts there must be gigantic to have a noticeable shadow on earth. Mass and technology far beyond our capabilities. We have already said it needs station keeping and steering because L1 is unstable (things fall out if not kept in place). Such a thing would be pushed away by the solar wind and solar radiation anyway. It won't work. The only thing that works is cutting down greenhouse gas emissions. – user18607 Jan 11 at 20:55 • It currently costs in the range of$1000 a pound to launch something into space. Given that you would need millions of square miles of mirror, a space mirror sounds very expensive. Putting the mirrors on the ground is a bit cheaper. – user4574 Jan 11 at 22:53
• @user4574 The mirror would only(?!?) need to be about 600,000 sq miles (155,399,287 hectare) in order to provide a 1% reduction in solar energy reaching Earth. That is about the same size as the US state of Alaska. Or about the size of France, Italy, Spain, and Portugal combined, for our European members. – krb Jan 12 at 4:47
• @krb The cross section of the earth that is facing the sun at any given moment is 49 million square miles. Taking into account that the mirrors will change angle as the earth rotates, and also that its night half the time you probably need more like 1.6 million square miles to reflect one percent of the light into space. – user4574 Jan 12 at 5:56

Of all the types of energy there is, heat is the "waste" of the energies. See, energy is only useful if organized, and heat is the least organized of them all. I.e, the energy must be able to push car wheel in that particular direction, not to every direction at random, like molecules of a hot gas would.

In order to reorganize the energy, according to the laws of physics (the second law of thermodynamics, in particular), you must have a cold place to where the heat could flow. Most (all?) heat engines relies on the environment being colder than the heat source in order for it to work: a car or a airplane engine only works because the ambient temperature is smaller than the temperature inside the engine, and a coal plant relies on the ambient being cooler than the steam turning the turbines.

By being immersed in a hot ambient, you can't use that very ambient as the cold side in order to extract energy from it, so you can't possibly build a device that is powered solely on the heat of the environment it is immersed in.

That is one half of the problem. The other is: if we could extract energy from the environmental temperature, we would certainly not radiate it away to space: we would use it as electricity, power our cars, planes, and would never need fossil fuels again.

Fossil fuel based energy is very inefficient; the amount of heat wasted exceeds that which gets used. In addition global heating from enhanced greenhouse effect is adding heat at rates estimated at around 100 times that from total waste heat. In order to get zero global heating (whilst continuing to burn fossil fuels) by collecting heat and sending it to space requires collecting in excess of a hundred times more energy than human economies are currently using as well as developing and building and operating the technology to send all that heat somewhere else, ie to space.

That is effectively impossible, but developing a means to utilise low grade heat for energy generation could significantly aid the displacement fossil fuel burning, that would reduce global heating by that factor of a hundred. Technology for turning low grade heat into higher grade energy exists - eg Stirling engines - but they are not cost effective. Some other tantalising possibilities do exist, such as Nantennas aka Optical Rectennas.

However, effective low emissions energy options that reduce fossil fuel use and the enhanced greenhouse warming and that are cost effective already exist; I think those should be the primary focus of our current response to global warming.

The problem with turning many forms of waste heat into other forms of energy by conventional (heat engine) methods is that significant temperature differences are needed - and that the temperatures making up the differences are counted from absolute zero (0 Kelvin). Only if that ratio is large, you get an efficient conversion. For example, if you look at the waste heat from a computer CPU, it might be at 340 Kelvin, 40 degrees Kelvin (Kelvins are absolute-zero-referenced centigrades for you Fahrenheit types) over an ambient temperature of, 300 Kelvin. You can't force the heat to build up to much higher levels since you will damage the CPU. The efficiency of a heat engine trying to make anything useful of this situation would be 40K/340K*100% = drumroll ... 11%. Hardly WORTH trying to recover.

This is because Carnot, one of the patron bastards of physics, made that the law in 1824, and no one repealed it yet.

This does not apply to heat radiation, which isn't heat per se but heat that has already been converted into long wave infrared light, which gets converted back into heat if it hits something. It can indeed be relayed at will by lenses, mirrors and prisms made of the appropriate materials (not: run of the mill window or optical glass!). Unfortunately, creating significant heat radiation is also something that takes high temperatures....

Well the most straight forward way to radiate sunlight into space is with a mirror.

But creating millions of square miles worth of mirrors sounds very expensive. Probably in the range of a 100s of Trillions of US dollars. If we got rid of all government spending we might be able to pay for it over the course of a 100 years or so.

• Yes! Increase the albedo! I quite like this answer because it's a shortcut which avoids heat, in other words, high entropy, which would need to locally be reduced again (at the expense of more energy and entropy) in order to create high temperatures. A mirror should work well because the atmosphere is transparent for the wavelengths reaching the ground which implies that they can readily leave without heating the atmosphere much. Since you seem to be politically conservative I suggest to call your idea to send the radiation right back at the border the Trump principle. – Peter - Reinstate Monica Jan 12 at 22:47

Mankind does collect natural sources of heat and turn it into useful energy: heat pumps, solar arrays, geothermal etc, but it would be impossible to reduce global warming in this way. Most of the heat collected for useful purposes is in any case given back to the atmosphere when the energy is used. If you think about it, even wind farms are collecting solar energy, because it is the sun's heat which drives the winds. When the energy is used, it is re-converted into heat. As a physics student you should know this.

• Yes, it is well possible to use regenerative energies like solar and geothermal to reduce greenhouse gas emissions and thus global warming. It is the greenhouse gases' trapping of IR radiation that causes warming. – user18607 Jan 9 at 18:06
• Oh maybe I expressed myself wrong - I dont study physics - I only had it as a subject in school :) Lets leave that factor of energy creation completely aside (which would be only even more beneficial but is not the point of my question). Would it work to dissipate more heat into space (by any means at all) to solve global warming? – Martin Eckleben Jan 9 at 19:16
• All the methods yet suggested of reflecting solar energy back into space, such as painting the deserts white, are environmentally unacceptable, as well as being prohibitively expensive.. – Michael Walsby Jan 9 at 19:21
• True, but no serious source suggests that. @MartinEckleben: energy can not be created, only transformed and converted. And yes, it would be trivially possible, by reducing greenhouse gas emissions to remove the atmospheric trap. – user18607 Jan 9 at 19:29
• @ebv "energy can not be created" Yup the three laws of thermodynamics I understand (at least their symptoms). OK removing the atmospheric trap would be awesome but I dont see the world being able to do that fast enough. If we could "actively" take heat (energy) away from the atmosphere and send it "actively" to space I feel humanity would maybe be more committed as no one would have to lose comfort or life quality. – Martin Eckleben Jan 9 at 19:47