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Anthropogenic-sourced greenhouse gases are commonly cited as the main source for human-caused climate change. However, something that I never see discussed is the actual heat produced by human activities. It could be that it's negligible, but I'm still curious to see quantitative data.

For example, a running engine in a vehicle produces $\ce{CO2}$ due to fuel combustion, but the engine also produces heat. What about heat produced from ovens, fireplaces, incandescent lighting, etc.? Ignoring the carbon footprint of such activities, can the heat alone be sufficient to affect the atmosphere on a global scale?

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  • $\begingroup$ Yes, it does cause some warming. The important thing that both sides never bring up is the fact that we won't be burning fossil fuels much longer. Burning stuff from the ground is so very very primitive. In about 50 years ... maybe a little more we won't be burning any fossil fuels. Why is everyone so worried about something that is on the brink of going away (burning fossil fuels). The damage we do over the next 50 years is very very very minor compared to all the benefits and progress of having energy. $\endgroup$ – slindsey3000 Feb 1 '17 at 16:31
  • $\begingroup$ @slindsey3000 You may call me selfish, but I'm worried because the damage we do over the next 50 years coincides almost perfectly with my remaining lifespan. $\endgroup$ – kingledion May 2 '17 at 2:15
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A recent study by Chen et al. (2014) in the article Anthropogenic Heat Release: Estimation of Global Distribution and Possible Climate Effect defined the heat release as you described as being Anthropogenic heat release (AHR), and has it basis as a product of economic prosperity, which leads to energy usage and excess heat produced - usually in large cities globally - this is sometimes referred to as 'waste heat'.

In their research, Chen et al report on an earlier global estimate made by Chen and Shi, 2012:

  • Globally, the estimated AHR is 0.03 Wm$^{-2}$
  • Over land, this average becomes 0.10 Wm$^{-2}$

Although, globally, these amounts are considerably less than that from $\ce{CO2}$ emissions, they still add to the problem - especially as the rate of urbanisation, hence the use of heat generating appliances is increasing rapidly, this value will become more significant.

However on a regional scale, over large cities for example, such as Tokyo, the effects of AHR are more profound. In and around the region around Tokyo city, the AHR can exceed 400 Wm$^{-2}$. So what are the consequences of this flux? Most of it causes regional effects, in particular (from Chen et al.):

  • Can influence urban climates and is a significant contributor to the urban heat island, which amongst other things can affect regional rain patterns.
  • Can affect the dynamics and thermodynamics of urban boundary layers.
  • Can influence the reaction rates and types of emitted aerosol and particulate species.

All of which have a compounding effect in the regional and to a lesser degree, global environment, that Chen et al. attribute to as being a cause of a 1-2K temperature rise in high altitude areas in Eurasia and North America and as a disrupting influence in global atmospheric circulation.

Edit 28/2/2016: There is an interesting blog post about a similar phenomenon: Dubai construction alters local climate

Additional references

Chen, B., and G.-Y. Shi, 2012: Estimation of the distribution of global anthropogenic heat flux. Atmos. Oceanic Sci. Lett., 5, 108–112.

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Disclamer: I am not an atmospheric or climate scientist; corrections are welcome if I have anything wrong.

Human heat production

According to the IEA, world primary energy consumption in 2012 was 13370 million tons of oil equivalent, which works out to being $5.6 \times 10^{20}$ Joules. Averaged over a year, this equates to $17.8\,\mathrm{TW}$. Wind, solar, etc., are a negligible part of this, but it does include a small but noticable amount of hydro and biomass. Strictly speaking, all of the hydro and some of the biomass should be excluded as they are simply a short-term "reuse" of energy that has already arrived from the sun, and not "new energy". Let us use the figure above but treat it as an upper bound.

The area of the earth is $5.1 \times 10^{14}\, \mathrm{m^2}$(source: Wolfram Alpha), which means that the figure above comes out to $0.033\,\mathrm{Wm^{-2}}$, a comfortingly close match to the figure given in the literature in Sabre Tooth's answer.

Energy from the sun

According to the Wikipedia page "Earth's energy budget", average solar insolation on the surface of the earth, taking into account day and night, summer and winter, is around $240\,\mathrm{Wm^{-2}}$. The figure that we should use is higher than this, as some is absorbed in the atmosphere and contributes to warming, but let us treat this as a lower bound. Multiplying by the surface area of the planet gives us an incoming energy flux of $1.22 \times 10^{17} \, \mathrm{W}$, or 122 petawatts.

Comparisons

Total human heat production, then, is in the order of 0.01% of the energy from space, and as such one might consider it negligible. By contrast, the total energy imbalance that results in global warming - including any effect from anthropogenic heating - is estimated to be approx 300 TW, or 20 times the total anthropogenic heat output.

(As an aside: Initially when writing this I thought "human fuel use is 5% of the planet's energy imbalance - that's significant!". But of course the greenhouse effect results in an imbalance that is a proportion of the total radiated energy, and human energy makes an insignificant difference to that total radiated energy.)

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  • $\begingroup$ It is very small but, what is its perturbing effect? Local scale unequal heating, however, small may cause big weather and climate effects. I can think of the Lorenz's " butterfly effect". $\endgroup$ – Gemechu Fanta Garuma May 17 '16 at 16:33
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Basically, we can ignore the heat we release compared to the effect of the $\ce{CO2}$ we release. To be more specific:

Heat we release has only a temporary effect because heat is radiating out to space. In fact you can get an idea of how long it takes for newly released heat to radiate away by checking how quickly temperatures drop when the sun sets. It's fast.

The heat we released a year ago is gone. In fact, probably the heat we released yesterday is basically gone. There's no cumulative impact. The extra heat we release now is effectively decaying exponentially in time as the system tries to get to its equilibrium, and its half-life is pretty short. However, that equilibrium it is trying to reach is determined in large part by the $\ce{CO2}$ concentration.

Our release of $\ce{CO2}$ is cumulative. The $\ce{CO2}$ we released 10 years ago is still having an impact on current $\ce{CO2}$ levels, and will continue to have an impact for many, many years. The $\ce{CO2}$ we release now is being added to this.

If we turn off industry, our impact due to heat released will be gone within days or weeks at most. Our impact due to $\ce{CO2}$ released will take much longer than a human lifespan.

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