Let's assume a world where humanity managed to stabilize the climate again and maybe even reversed the effects of the current climate change. (So that we can ignore the current global warming in this question.)

In this world humanity grows further and builds more machines and electronic devices for an ever increasing standard of living. All of them are extremely optimized to have minimal energy consumption and such but no matter what we do each device (and each living being) produces some waste heat even if it is not much.

How realistic is it that in this world the waste heat will ever contribute significantly to the temperature of earths atmosphere?

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    $\begingroup$ Seems answered by en.wikipedia.org/wiki/Waste_heat#Environmental_impact $\endgroup$
    – user535733
    Feb 19 '20 at 16:56
  • $\begingroup$ Renewable energy doesn't generate excess waste heat, so if we stabilized climate by relying on sources like solar and wind this wouldn't be a problem. On the other hand, if we start building huge numbers of nuclear power plants (fission or fusion), or even solar satellites that collect light above the atmosphere and beam power down, it could be a problem several centuries from now (see the article here). In a civilization that advanced a lot of people might be living off-world though. $\endgroup$
    – Hypnosifl
    Feb 19 '20 at 17:02
  • $\begingroup$ @Hypnosifl If I am not mistaken, the type of waste heat based global warming you reference was also included (as a world-building aside, not as a plot point) in Arthur C. Clarke's 3001. $\endgroup$
    – tbrookside
    Feb 19 '20 at 17:07
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    $\begingroup$ @Hypnosifl I would argue that e.g. solar panels come with waste heat, as they channel energy into the earth system which otherwise would have been reflected back to space. $\endgroup$
    – M. Winter
    Feb 19 '20 at 17:17
  • $\begingroup$ Eventually, civilization will want more energy than can be harvested renewably without (for instance) competition between solar collectors and cropland becoming a major issue. Fusion, the only genuinely long term solution, does produce waste heat, both in generation and in use of the electricity it produces. If we can't make a Dyson swarm before we outstrip Earth-based passive solar, fusion will be the only way out. $\endgroup$
    – Zeiss Ikon
    Feb 19 '20 at 17:23

Waste heat (on planetary scale) is not an issue today, and likely not going to be an issue for the next 100 years and even more. But as the civilization approaches a full Kardashev I level, it inevitably should deal with waste heat. Either through decreasing planetary albedo (for effective energy capture), or by building space collectors, beaming energy to the surface, or via other, non-solar sources like fusion, energy balance of the planet will be shifted.

An obvious answer here is moving all energy-intensive operations to space. Over there, we can spread our infrastructure as thin as we like, eliminating the heat issue.

One logical consequence of this approach is that planet-bound civilization can never truly achieve Kardashev I level. We can get close to capturing all solar energy reaching Earth, but some percentage of it would inevitably go to waste heat, so we should be careful with maintaining Earth's albedo.

Are there any ways to cool a Kardashev I planet? Yes, it is possible to build radiant "planetary air conditioners". However I can not estimate their net effect on a planet and can not tell if they would be practically feasible.

  • $\begingroup$ 100% of energy inevitably goes to waste heat. Once waste heat begins to be significant, simply start installing infrared blocking shades between the sun and the earth to offset the heat. $\endgroup$ Feb 19 '20 at 19:38

The simple way to avoid problems with waste heat on Earth is to gradually move the most energy intensive aspects of human civilization off world. As more and more energy using and waste heat producing activities go off world, a larger and larger percentage of the human population will live in space close to energy using activities, and a smaller and smaller percentage of the human population will live on Earth, until eventually all humans might live in space habitats and Earth might be maintained as a nature preserve.


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