From 'The Solid Earth' by CMR Fowler (the geophysics book closest to my desk), the Earth's surface heat flux is 44 TW. This is not the total heat energy in the

From 'The Solid Earth' by CMR Fowler (the geophysics book closest to my desk), the Earth's surface heat flux is 44 TW. This is not the total heat energy in the earth, it's the amount of internal heat (from the sources you've specified) radiated into space every second. I think that the difference between 44 and 51.9 is not budgetary (in the sense that the 8 TW difference is a different source) but reflects uncertainty in the estimates. This is just to clarify what the numbers really mean, in case anyone thinks ~50 TW is the total heat energy (i.e. mass * heat capacity * absolute temperature) of the earth. My back of the envelope calculation is the total heat energy (m * Cp * T) = 2.5 E 31 W, using mean temperature of 4500 K (mantle) and 11000 K (core), Cp 1000 (mantle) and 450 (core) (in J / kg), and the fraction of the earth's total mass (6E24 kg) made up by the mantle (0.6) and core (0.3). I'm ignoring temperature dependence of heat capacity because I don't want to look it up. And ignoring latent heat, and other simplifications...