We know that global warming has a component caused by greenhouse gases, but I was wondering how much of the heat is caused directly by burning fuel.

I made this classification to explain what i am referring to.

Global warming causes:

  • Natural causes
  • Artificial causes
    • Indirectly by releasing CO2 and other greenhouse gases
    • Directly by burning fuel
    • Other

I guess the overall heat directly released by burning (not taking into account the CO2 released) is still relatively small.

Second part. What if we finally achieve "almost free" energy (i.e. nuclear fusion)? What if we reach the point where anyone can make their own reactor on their backyard?

For the sake of my argument, imagine 1 billion fusion reactors on earth, how much heat would that generate, and how that may affect temperature. At what point the temperature increase would be comparable to that caused by greenhouse gases?

Anybody dare to do the numbers?

Edit: Maybe I should have been more polite in my question. Anyway, the number i've taken from the responses is that this direct heat release is about 1% reponsible for global warming. So, as I understand it, we still have 1 or 2 orders of magnitude left for clean energy generation before it creates the same problem as greenhouse gases.

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    $\begingroup$ I'm fairly sure this is a duplicate. The answer is this is insignificant. $\endgroup$ Jan 6, 2023 at 16:57
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    $\begingroup$ I'm not the downvoter, but you are probably being downvoted for the purely hypothetical stuff at the end of the question. This is not the site for questions that specifically ask for unverifiable opinions. I suggest you take that latter part to the Worldbuilding StackExchange site. $\endgroup$ Jan 7, 2023 at 13:24
  • $\begingroup$ the ending of your question:Anybody dare to do the numbers?.science is the numbers and nothing else,science does not belive in climate change it is not a religion,science is about what can be measured and quantified opinions does not have a place in science. $\endgroup$ Jan 7, 2023 at 14:45
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    $\begingroup$ i did not downvote your question but i can understand why somebody might do it. $\endgroup$ Jan 7, 2023 at 15:53

1 Answer 1


A 2009 study - "Integrating anthropogenic heat flux with global climate models" by Mark Flanner found anthropogenic waste heat - which includes all energy used as well as wasted from non-renewable energy sources, ie energy from nuclear and fossil fuels - to be +0.028 W m−2 or about 1% of the climate forcing from enhanced greenhouse effect. It contributes to urban heat island, ie affects local areas at greater than the global average, and Flanner suggested it should be included in climate modeling to better show how much warming in urban areas.

Another study Anthropogenic Heat Release: Estimation of Global Distribution and Possible Climate Effect (2014) shows similar values.

So there is a contribution to global warming from anthropogenic heat release but 99% of global warming is from other causes - with enhanced greenhouse from CO2 (from fossil fuel burning) being the single largest warming influence. And atmospheric aerosols (from fossil fuel burning) the largest cooling influence.

I don't know if it included in the "Other Human Drivers" or not but this is from IPCC AR-6 SPM -

Contributions to warming


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