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According to Earth's internal heat budget (Wikipedia) “About 50% of the Earth's internal heat originates from radioactive decay”.

However, this makes up only a small portion of the Earth’s heat budget due to the large input of solar heating.

How much cooler would the Earth’s surface be if there was no contribution from radiogenic heating?

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  • $\begingroup$ The entire heat budget is irrelevant for the surface temperature - no matter how much is radiogenically generated. $\endgroup$ Commented Nov 16, 2023 at 21:42
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    $\begingroup$ If Earth is at thermal equilibrium, it radiates as much heat as it receives (solar) and generates (radiogenic, gravitational, tidal and geologic). Thermal radiation varies with the 4th power of absolute temperature. If heat production (in this case, radiogenic) increases, the surface temperature increases until equilibrium is re-established. $\endgroup$
    – Woody
    Commented Nov 16, 2023 at 22:11
  • $\begingroup$ Yes, generally it is $F_{internal} + F_{stellar} = F_{emitted}$, but since $F_{internal}/F_{stellar} \ll 1$, it is irrelevant. "Thermal radiation varies with the 4th power of absolute temperature. " Your point being? Radiogenic heat doesn't magically scale up to the fourth power, just to establish equilibrium. $\endgroup$ Commented Nov 16, 2023 at 22:16
  • $\begingroup$ Thanks for the thoughtful question and answer. However, isn't the salient question about whether the 100M barrels of oil+ we have been pumping out of the mantle has reduced the previously provided radiation/heat barrier and whether the global 1.2 trillion ton+ ongoing ice melt isn't indicative of a growing heat imbalance? I hope this discussion grows as we record one global/regional heat record after another. $\endgroup$ Commented Nov 20, 2023 at 17:52
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    $\begingroup$ well without it plate tectonics would stop, which would stop almost all volcanics, which cool the planet just through the loss of co2. $\endgroup$
    – John
    Commented Nov 21, 2023 at 21:50

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