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I had been thinking about the way an air conditioning system moves heat from one place to another. The unit runs and drops the temp. in the building and raises the temp. outside. Also there is mechanical energy that converts to heat (the compressor and fan motors) and is also put outside. If this is the case, is there an effect caused by A/C systems running on the outside temp.?

Can the total amount of heat being moved from inside to outside contribute to global warming? Consider how many systems there. As more and more A/C systems are installed and more and more buildings built, can't this lead to (if it hasn't started already) a higher temp outside?

I am not a scientist; if this question is wrong, I would like to know why.

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  • $\begingroup$ It does with the urban heat island effect. However, the CO2 from the generation of the energy warms the Earth about 10,000 times more. $\endgroup$
    – Alan Rominger
    Jul 14, 2014 at 2:25

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The heat energy being moved does not contribute to any global warming. The A/C is simply moving energy from inside to outside; the heat just turns around and flows back into the room, and the total stays the same. It's like someone trying to keep a leaky boat from sinking; you dump some water over the side, and it (or some just like it) leaks back in. A certain capacity pump can keep the water level in the boat low enough for the boat to survive. The A/C does the same for our houses.

But...

The energy used to drive the A/C is a different matter. Depending on the source of this electrical energy, there could be a minor contribution to global warming.

If the electricity came from fossil fuels, then the energy is stored solar energy from whenever the fossil fuel was first formed from atmospheric carbon dioxide by plants using sunlight. You could say that the energy absorbed by plants through photosynthesis kept the earth somewhat cooler than it otherwise would have been, and now we're "correcting" this by burning the fossil fuel back to carbon dioxide.

Here in Ontario, much of our electricity historically came from hydro-electric plants, like Niagara Falls. Does this contribute to global warming? Not really... Sunlight (energy) falls on the ocean. Some of this energy warms the water. The rest evaporates some water, lifts it kilometers into the air, and lets it fall as rain on elevated land. As this water flows back to the ocean, it converts its potential energy into kinetic energy, and then into heat. The water flowing away from Niagara Falls is slightly warmer than the water at the top. But, if the water goes through a generator on its way down, electrical energy is extracted, and the water is cooler than it otherwise would be. So, the heat produced in Toronto by using electricity is exactly balanced by the slightly cooler Niagara River. Eventually all the water makes it back to the ocean, and all the original solar energy is converted to heat...

As commented by @AlanSE, the negative effect of the carbon dioxide in the atmosphere greatly outweighs these energy transfer effects...

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    $\begingroup$ Even if the electricity was generated at, say, nuclear power plants, which don't produce CO2 but do release quite a lot of waste heat, the effect on global temperature would be quite minimal, because the Earth is in a similar dynamic equilibrium as the boat in your analogy. The Sun radiates heat to the Earth, and the Earth radiates the same amount of heat away. If there's an additional source of heat, the heat radiation simply increases. CO2 disturbs this balance by reducing the heat radiation. $\endgroup$
    – ntoskrnl
    Jul 14, 2014 at 10:42
  • $\begingroup$ I appreciate the answers to this. I was not sure just how minimal this effect would be but know I think I understand it. THANKS!! $\endgroup$
    – Cbow0516
    Jul 14, 2014 at 10:46
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    $\begingroup$ "we're "correcting" this by burning the fossil fuel" -- true, and the Jurassic was fun in all sorts of ways. Although people tend to look at you funny if you go any further than this, for example by saying that oxygen is the primary artificial atmospheric pollutant and we should correct this by wiping out everything that photosynthesizes to get back to nice, wholesome anaerobic bacteria ;-) $\endgroup$
    – Steve Jessop
    Jul 14, 2014 at 15:32
  • $\begingroup$ The heat energy being moved may not contribute; but the method used to move the heat energy would contribute. The pumps/compressors in AC units would generate heat from electricity. It's not as simple as "this all came from the sun so it evens out". Every time you are converting the energy you generate more entropy which reduces the useful energy on the Earth turning it to heat instead. $\endgroup$
    – JMac
    Sep 6, 2018 at 10:50
  • $\begingroup$ Interesting would be if the A/C was powered by PV solar energy. In this case, the amount of electricity would otherwise have turned into sun radiation heat, now converted to electricity - used and again turned into heat, making the system temperature neutral? Is that correct? $\endgroup$
    – Bachi
    Aug 3, 2021 at 7:26

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