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Greenhouse warming 100 times greater than waste heat

What the science says...

Select a level... Basic Intermediate

Greenhouse warming is adding 100 times more heat to the climate than waste heat.

Climate Myth...

It's waste heat

"Global warming is mostly due to heat production by human industry since the 1800s, from nuclear power and fossil fuels, better termed hydrocarbons, – coal, oil, natural gas. Greenhouse gases such as carbon dioxide (CO2 play a minor role even though they are widely claimed the cause." (Morton Skorodin)

At a glance

There are various kinds of climate science deniers out there, but one grouping can usefully be classified under the acronym ABCD - Anything But Carbon Dioxide. These people appear to accept the climate is heating up. Flailing around to try and identify something other than CO2 causing the heating, they will seize upon all sorts of candidate causes. This is one of them. There are many others.

All the energy we use dissipates into the environment post-use, be it a driftwood fire on the beach or the heart of a busy metropolis, on the go 24-7. So it should come as no surprise that 'waste' heat does have a role - a minor one - in heating the planet. Humans have always been fond of fire since they learned to ignite things and there's nothing better than sitting round a blaze of a night with a few friends. No need to feel guilty about that. It's harmless in the overall scheme of things.

Waste heat is of course a much studied subject. After all, more sophisticated heating systems, compared to that fire on the beach, are energy-intensive and that translates as expensive. Ways to minimise heat loss and thereby improve efficiency form an active research topic. In that sense, a number of studies have looked at the bigger picture: just how much waste heat is there?

Unsurprisingly, cities, where huge numbers of people work, rest and play, are megacentres of heat wastage. The term, 'Urban Heat Island', acknowledges this. But the planet is a big old place and cities occupy relatively small parts of it. To find the warming contribution of waste heat, you need to have two figures: the total energy lost and the surface area of the planet. Doing the maths you can then derive the amount, expressed in watts per square metre. You can then compare it to other heat sources.

All studies of waste heat have arrived at a similar conclusion. There's a lot of waste heat over cities but the total, global amount, expressed as watts per square metre of the planetary surface, is a tiny fraction of the heating caused by the greenhouse gases. So while it's highly desirable to find better efficiencies in energy use and conservation, thereby saving money, when it comes to temperature it's greenhouse gas emissions we have to hold firmly in our focus. ABCD indeed. Next.

Please use this form to provide feedback about this new "At a glance" section. Read a more technical version below or dig deeper via the tabs above!

Further details

Heat is released to the atmosphere as a result of human activities, many of which involve combustion of fuels, directly or indirectly. Sources of this 'anthropogenic heat' include industrial plants, heating of buildings, air-conditioning, vehicle exhausts and many more. In cities, anthropogenic heat typically contributes 15–50 W/m2 to the local heat balance, and several hundred W/m2 can be reached in the centres of large cities in colder climates.

This heat doesn't just disappear - it dissipates into our environment. How much does waste heat contribute to global warming? There have been several studies over the years, widely-cited examples being Flanner (2009) (if you want to read the full paper, access details are posted here), Dong et al. (2017) and Varquez et al. (2021). All have come up with similar numbers despite differences in methodology: the core message is that while waste heat is an issue and is self-evidently undesirable, its contribution to global warming is a tiny fraction of that brought about by CO2.

Flanner concluded that the contribution of waste heat to the global climate was 0.028 W/m2. That was with respect to the mid 2000s. In contrast, the contribution from human-emitted greenhouse gases at the time was 2.9 W/m2 (fig. 1). So in the mid 2000s, waste heat amounted to about 1% of the total warming, with greenhouse gases making up much of the rest. The above numbers refer to radiative forcing, the change in energy flux at the top of the atmosphere. Or putting it in plain English, the amount of heat being added to our climate.

Relative radiative forcings due to waste heat and CO2.

Fig. 1: the relative radiative forcings due to waste heat and CO2 in the mid 2000s, from the numbers presented by Flanner (2009).

Since that time, both greenhouse gases and energy use have gone up (fig. 2), so it should come as no surprise to see increases in radiative forcing in both cases. Future projections have largely been focussed on recovery of the waste heat, such as that by Firth et al. (2019). An important conclusion of theirs is that, "full recovery of the theoretical potential is found to lead to a 10–12% reduction in the combined forcing of CO2 and waste heat over this period, mainly due to a reduction in CO2 emissions."

An important point to consider here is that the warming from thermal energy production occurs when a fossil fuel undergoes combustion. Whoomph! and that's that - the energy is produced in a single pulse then dissipates away. In contrast, warming from the emitted CO2 continues for the lifetime of CO2 in the atmosphere - potentially thousands of years (Zhang & Caldeira 2015). Zhang and Caldeira showed that "the energy released from the combustion of fossil fuels is now about 1.71% of the radiative forcing from CO2 that has accumulated in the atmosphere as a consequence of historical fossil fuel combustion." Again a small fraction of the CO2 radiative forcing, and emphasising the issue of the cumulative build-up of CO2 due to its relatively long atmospheric residence time.

Total energy use on Earth.

Fig. 2: total energy use on Earth, 1800-2023.

To conclude, greenhouse warming is currently adding some 60-100 times more heat to our climate than waste heat. That's not to say we should not be bothered about waste heat though, There are many sound reasons, including economic, for reducing heat wastage. It makes no sense at all to tolerate systems that for various reasons are grossly inefficient. But that needs to be considered as a separate entity from the huge problem of human CO2 emissions.

Last updated on 7 January 2024 by John Mason. View Archives

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Comments 1 to 25 out of 204:

  1. In 1983 I asked my Dad if it was warmer outside because everyone was running furnaces to heat their houses. He said yes.
  2. Somebody's crunched numbers. Small globally, noticeable regionally: Nearly all energy used for human purposes is dissipated as heat within Earth's land–atmosphere system. Thermal energy released from non-renewable sources is therefore a climate forcing term. Averaged globally, this forcing is only +0.028 W m−2, but over the continental United States and western Europe, it is +0.39 and +0.68 W m−2, respectively. Here, present and future global inventories of anthropogenic heat flux (AHF) are developed, and parameterizations derived for seasonal and diurnal flux cycles. Equilibrium climate experiments show statistically-significant continental-scale surface warming (0.4–0.9°C) produced by one 2100 AHF scenario, but not by current or 2040 estimates. However, significant increases in annual-mean temperature and planetary boundary layer (PBL) height occur over gridcells where present-day AHF exceeds 3.0 W m−2. PBL expansion leads to a slight, but significant increase in atmospheric residence time of aerosols emitted from large-AHF regions. Hence, AHF may influence regional climate projections and contemporary chemistry-climate studies. Flanner, M. G. (2009), Integrating anthropogenic heat flux with global climate models, Geophys. Res. Lett., 36, L02801, doi:10.1029/2008GL036465.

  3. The central concern of man-made CO2 emissions has to do with its IR absorptive qualities, and for this reason it is referred to as a "greenhouse gas". Given that CO2 represents a very small percentage of the Earth's atmosphere, and in respect to the particular concerns, the implication is that its efficiency to radiate and absorb IR must contrast substantially with that of N2 and O2. The effect of greenhouse gas warming has to do with final results, such as the melting of polar caps and glaciers, and the warming of ocean water and land as well as the N2 and O2 that make up 97% of the Earth's atmosphere (i.e. climate change). Exothermic man-made industrial waste heat involves IR emission, but most of this heat consists of direct convective heating of both water and air. The idea that a significant portion of global warming could be attributed to industrial waste heat resides in the question of how N2 and O2 dissipate heat when its temperature is elevated beyond mechanisms that are normally found in Nature. While N2 and O2 (the bulk of the Earth's atmosphere) are not the best radiators at nominal atmospheric temperatures, they do cool nicely convecting to cooler water and ice, so as to provide a heat channel from one's home or automobile directly to oceans, glaciers and polar caps. On the other hand, it can be assumed this system is lossy to some degree in that CO2 picks up some of this energy and sends it upward to the heavens, but for all practical purposes, energy that enters the atmosphere stays here on Earth. For however small this energy may be, if it is accumulating, we should begin to notice it as something that is building slowly (i.e., hocky stick graph). And addressing those that dismiss waste heat on arguments based on numerics, it is not a matter of comparing a figure of forcing per square meter if this heat is not efficiently involved with radiative processes. In other words, if N2 and O2 are not GHGs they can only deliver heat by convection to cooler places.
  4. RSVP errata (a) but for all practical purposes, energy that enters the atmosphere IN THIS WAY stays here on Earth. (b) can only deliver heat by convection to cooler places (i.e., global warming).
  5. RSVP, there's no difference between heat that enters the atmosphere via radiative absorption and heat that enters the atmosphere as waste heat. It's not that one "accumulates" and the other doesn't. It's just that, globally averaged, the quantity of watts from waste heat is much smaller than the quantity of watts from absorption by GHGs. Doug kindly provides the numbers in his comment before yours. Globally, waste heat is roughly two orders of magnitude below the sum of CO2, CH4, N2O, and halocarbons. It's not zero, but it's negligible.
  6. RSVP at 19:53 PM, to determine whether or not waste heat is accumulating and contributing to global warming, it's only necessary to go back to the very basics. If the rate at which the planet is warming is less than that which waste heat adds, then NO, waste heat possibly does not contribute to the global warming and is dissipated. However, if the rate of global warming is greater than that which waste heat adds, then YES waste heat must both contribute, and continually accumulate year upon year.
  7. Sorry, johnd, but that's not particularly logical. Re your first statement, one could imagine a scenario where waste heat was contributing a huge warming forcing, but it was being countered by an even larger cooling forcing. The fact that the (imaginary) planet was cooling overall wouldn't negate the actual warming effect of waste heat. Re your second statement, the candles on my dining room table must "contribute" to warming the global atmosphere, too. But not in any meaningful amount! This is why it's important to quantify forcings, which is exactly what Doug Bostrom does in his comment upthread. Globally, waste heat is two orders of magnitude below greenhouse gases in its importance. Saying that non-quantitatively it must "contribute" is pretty much useless.
  8. RSVP, let's for the moment assume that the 'waste heat' argument isn't complete nonsense. Temperatures are still rising at the same rate. Humans are still causing it (i.e. it is still "AGW"). Fossil fuel use is still the source. What then should the proper course of action be? Under this view the rising temperatures which have been observed are due to the buildup of heat from burning fossil fuels over time. Does this not argue for converting from fossil fuels to renewables like solar and wind? The only significant difference is that nuclear power is out as an alternative because it is just as much a 'waste heat' generator as fossil fuels. So... that would suggest that you should support all the changes being suggested by AGW proponents EXCEPT that you should be against nuclear power. Is that the case?
  9. "Ned at 21:38 PM on 26 July, 2010 RSVP, there's no difference between heat that enters the atmosphere via radiative absorption and heat that enters the atmosphere as waste heat. " I agree. Heat is heat. However how it gets to the atmosphere is different. Internal combustion engines for instance are very efficient in the way they employ convection to rid themselves of excess energy. The car's radiator heats N2 and O2 directly, pushing cool air over a large surface areas. Heat that accumulates on a boulder during the day on the contrary, cools for the most part via radiation. Most all of that energy makes its way into outer space. If this was not true, the Earth would not maintain its temperature equilibrium. The AGW theory precisely points to anthropogenic CO2 as improving the "efficiency" of the atmosphere in capturing this radiated energy, even though most of this energy passes through like a sieve (i.e. the atmosphere is IR opaque in relation to "GHG" concentration.) Another way to explain this... If CO2 heat capturing efficiency is 5% (I am making this up for sake of the discussion, and referring to the efficiency of CO2 to pick up heat that warms the air), as compared 90% efficiency of convective heating of say an air conditioner. If I have 100 joules, in the first case, I am only going to warm the atmosphere by 5 joules, whereas with my air conditioner it will leave 90 joules.
  10. RSVP, the radiative forcing from CO2 (and other GHGs) only includes the outgoing longwave radiation that is actually trapped within the atmosphere. It doesn't need to "get to the atmosphere"; it occurs within the atmosphere. All of your arguments about waste heat accumulating in the atmosphere apply in exactly the same way to heat from GHG forcings. The only difference is that GHGs produce vastly more heat.
  11. CBDunkerson at 23:01 PM on 26 July, 2010 "What then should the proper course of action be?" I personally dont think humans are better off changing the chemistry of their atmosphere. And the challeges are huge. As such, we better get our ps and qs straight. There is no guarantee that the ill effects of global warming are going to be sufficient to stop fossil fuel burning. It might even be the biggest straw man to justify continuing to do so. If on the otherhand it turns out that higher CO2 levels has profound ill effects on the biosphere (for who knows what reasons), then that is where the science and effort should be dedicated.
  12. RSVP - Do you not remember our conversation over GHG's acting as an IR antenna? Energy goes into the atmosphere (conduction/convection from your automobile radiator, household AC, LWR from the ground. The air mass from this energy acquires a certain temperature. The source doesn't matter, just the total energy! GHG's radiate over their thermal spectrum based upon the temperature of the air mass. The 'waste heat' (mis)issue is that total industrial waste heat is 2 orders of magnitude smaller than the GHG forcing, the extra solar energy held by greenhouse gas increases. Those are the numbers, RSVP, waste heat is only 1% of the problem, hence nobody is really worried about it.
  13. Ned "All of your arguments about waste heat accumulating in the atmosphere apply in exactly the same way to heat from GHG forcings. The only difference is that GHGs produce vastly more heat. " The bulk of the atmosphere is N2 and O2. Most of the heat radiating off of the Earth goes up and out, otherwise we would have temperatures like the hot sidewalk midday. If a photon happens to excite a CO2 molecule, this energy may or may not make it to a nearby N2 or O2 molecule. All this describes a not so efficient heat capturing system. Nearly all the heat passing over a heat engine elevates the temperature of N2 and O2 directly (through convection). These gases in turn are not good emitters of radiation.
  14. KR "RSVP - Do you not remember our conversation over GHG's acting as an IR antenna? " I do. :) KR "The source doesn't matter, just the total energy! " I disagree. The efficiency of energy capture is what matters.
  15. RSVP "The efficiency of energy capture is what matters. " Example... Depending on the material, an object placed in a microwave oven may or maynot get hot. This is how it works.
  16. RSVP, if the CO2 molecule re-radiates the IR, the energy leaves with the photon. If not, the CO2 heats up, and hence the air mass does as well. The thing is, given the average path length before absorption for surface pressures and GHG concentrations, the photon will hit another GHG molecule before it's gone very far at all. There are so many chances for absorption that it's not going very far. So that energy will add/subtract repeatedly to the energy of the air mass, and to its temperature. If first you don't succeed, try try again... really expresses this. The only way that energy leaves/cooling occurs via LWR is if the sum of emission events is higher than the sum of absorption events - which happens at the surface (396 W/m^2 going up, 333 W/m^2 going down), between the layers of the atmosphere as it cools with height and absolute GHG concentration drops, and the top of the atmosphere (238.5 W/m^2 LWR going out).
  17. CBDunkerson #8 "So... that would suggest that you should support all the changes being suggested by AGW proponents EXCEPT that you should be against nuclear power. Is that the case? " Renewable does not guarantee avoidance of warming. A black solar panel lowers the planet's albedo for instance. This is however getting off topic.
  18. KR "The only way that energy leaves/cooling occurs via LWR is if the sum of emission events is higher than the sum of absorption events " I assume you are talking about diffusion at some atmospheric boundary layer. However if I was passing overhead on a satellite pointing my IR detector towards the ground, I assume I would "see" IR energy as long as it was "brighter" than this intermediate IR "cloud". In other words, the GHG issue you are talking about is real but subtile, not unlike being able to see fog lights through daytime fog. The point being that if the ground is hot enough, the IR energy will make its way out.
  19. RSVP writes: The bulk of the atmosphere is N2 and O2. Most of the heat radiating off of the Earth goes up and out, otherwise we would have temperatures like the hot sidewalk midday. And the heat that goes "up and out" is not included in the stated radiative forcing for CO2. Thus, we can directly compare the radiative forcing from CO2 to the waste heat forcing. As has been pointed out over and over again, the latter is two orders of magnitude smaller than the former.
  20. RSVP, it would help if you would please give us a reference to a paper or a study that shows that the magnitude of the forcing from waste heat has been dramatically underestimated and that it's comparable to the 2.5 W/m2 from greenhouse gases.
  21. RSVP - yep, a glowing fog is all you would see from a satellite at GHG wavelengths. You need to choose a different wavelength (visible, for example) to resolve ground objects. You still have not addressed the base issue of this thread, however. That is the fact that all industrial energy production (waste heat, used energy that eventually becomes heat via entropy, etc.) sums up to a number 2 orders of magnitude smaller than the GHG entrapment of solar energy. If we were to convert all energy production to solar power, with a decrease in Earth albedo, the 1-2% forcing gain in albedo and solar panel waste heat inefficiencies would be more than balanced by the 99% decrease from GHG entrapment. See the RealClimate estimates of energy balance from solar replacement of fossil fuels.
  22. RSVP wrote: "I personally dont think humans are better off changing the chemistry of their atmosphere." Sooo... you agree that we shouldn't be emitting all that CO2. Excellent. That said, a few things which need explaining if you want to continue running with this 'global temperature increases are being caused by waste heat' bit; 1: Why are temperature increases most pronounced at the poles... where there is virtually no industry generating waste heat? 2: Why do we not see huge spikes of increased heat around urban industrial centers gradually leveling off as you get further into non-industrial regions? 3: Why has warming been most pronounced at night and during Winter? That makes sense if the warming is due to decreases in the rate heat escapes... but not if it is due to increasing 'accumulated heat'. 4: Why is the stratosphere cooling? Again, that makes sense if heat is being prevented from escaping to the stratosphere... but not if the total heat of the planetary environment is increasing. Those are just a start. There are dozens of other things which clearly indicate that 'waste heat' is not the cause... even setting aside issues of scale.
  23. CBDunkerson, those are all interesting questions. For me, though, they're secondary. Being a skeptic by nature, I'd like to see some evidence from RSVP, in the form of a paper or a study or some actual data. Until something like that is presented, why should anyone care about waste heat? Flanner 2009 calculates that it's minuscule, and RSVP hasn't given us any references to contradict that.
  24. Ned, many deniers assume that all data which contradicts their beliefs has been faked. Thus it may help to present proofs based on basic logic in addition to those based on data. Or not. Some are impervious to both.
  25. Yes, CBD, I think that's a useful approach for many topics here. In this case, though, RSVP hasn't offered any empirical evidence in support of his claims for waste heat. Well, I'm a skeptic. I want to see some evidence before I concede that it's even worth discussing.

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