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My question relates to the fact that 1- the human population is continually increasing, and 2- everybody is constantly 'doing more stuff' (or causing more to be done). So doesn't 'more people doing more stuff' heat the environment correspondingly more and contribute directly to 'global heating'? Yet I have never heard of this argument, only that of increased greenhouse gas emissions blocking the dissipation of solar heat. I leave out the fact that, as people age, at some point they do a lot less stuff. (However, could they still cause overall even more stuff to be done, e.g. when they get sick and need intensive infrastructure -- care, transport, medicines, operations etc.)

There seems to be the general perception, or claim, that everything is 'getting more efficient', so we are thereby using less energy (and heat production, in my above model?). But some comentators say that this just leads us to use a lot more of the new, more efficient technology, so that overall energy consumption and heating increases. Could telephone use today per capita (and over some unit of time) actually consume less energy than it did in, say, 1960? Offhand, it seems unlikely, especially since the definition of 'telephoning' today is much broader than the 1960s' activity.

Could increasing direct heating of the earth by human activity perhaps not explain why, at present, we are seeing consistently higher global warming measurements than were only recently predicted? (Today's Guardian headline: 'Climate crisis: alarm at record-breaking heatwave in Siberia -- Unusually high temperatures in region linked to wildfires, oil spill and moth swarms'.) (Just consider how much 'new heat' is caused indirectly and directly by one more rocket launch. And of course there isn't 'just one more', but many more.) To be sure, a lot of this heat dissipates with time into space by natural processes. But isn't the global warming argument that the sun's heating of the earth is being accumulated in the greenhouse effect, so why shouldn't the 'direct' heat from human activity, released into the environment, also be captured and add to the overall effect? (Apologies to the experts here who may find my proposal much too simplistic, but I would be interested to hear why.)

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  • $\begingroup$ An average human body emits ~100 W (value used by architects). So with 7 billion humans, the global population emits ~7 10$^{11}$ W. According to the IPCC (see this figure ipcc.ch/site/assets/uploads/2018/02/Fig-1.04-01-2.png), the total radiative forcing caused by humans is ~2 W/m², so ~10$^{15}$ W over the area of the Earth. More than a thousand times the heat radiated by our bodies. $\endgroup$ – Jean-Marie Prival Jun 18 at 7:32
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    $\begingroup$ This question is very related (borderline duplicate): earthscience.stackexchange.com/q/3041/725 $\endgroup$ – Gimelist Jun 18 at 7:55
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    $\begingroup$ @Jean-MariePrival Yes, and it's effectively net-neutral because that corporeal radiation is just reemitting energy that was very recently absorbed by primary producers (i.e., photosynthesis). It's a part of the surface energy budget that's so small we don't include it in climate models. $\endgroup$ – Deditos Jun 18 at 9:03
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It does, but globally it's negligible compared to other heat flux densities.

Simply do the math:

  1. World wide primary energy consumption: 162,494 TWh (2018)
  2. Hours/year (2018): 8760 h
  3. Earth surface: 510,100,000,000,000 m²

Assuming all this energy is transformed to atmospheric heating, this is an average heat flux (𝜙q=E/t*A) of 0.036 W/m². Locally this varies widely depending on climate (and the necessity to heat or cool buidlings), the degree of industrialisation, the population density etc. One figure I've found in Wikipedia for Germany: 1.2 W/m², Antarctica obviously: more or less 0.0 W/m², Hongkong (2018) 40.2 W/m² (calculated myself). BTW the average geothermal heat flux is 0.087 W/m².

Compare this to the solar contant: 1361 W/m². Considering albedo, day & night etc. the average (solar short wave) flux density on Earth's surface is ~ 175 W/m². The atmospheric back radiation is ~ 300 W/m².

So the average solar short wave flux density on Earth's surface alone is ~ 4,850 larger than the heat flux density directly induced by human energy consumption.

The heat flux density indirectly induced by human energy consumption (CO₂-, CH₄-, N₂O- etc. accumulation in the atmosphere) currently adds up to netto ~ 2.3 W/m² additional back radiation, which is roughly 60 times larger than the directly induced heat flux density.


Conclusion: direct heating of the atmosphere caused by energy consumption is almost insignificant compared to other effects.

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