We generally tend to underestimate sizes and masses of planetary, let alone stellar bodies. A little giveaway is that for all non-astronomical means and purposes we consider the earth's mass *infinite* without any measurable error.

Let's make an estimation. Let's assume that the average specific heat of the earth's matter is that of granite, 0.8 J/g. This leads to the following results:<sup>1</sup>

<pre>Specific heat of Granite (J/(kg*K))             8.00E+2
Earth's mass (kg)	                            5.97E+24
Earth's energy/K                            	4.78E+27
	
World primary energy supply 2015 (Mtoe)         1.36E+4
J/Mtoe	                                        4.19E+16
World primary energy consumption 2014 (J)	    5,60E+20
--------------------------------------------------------
Years of world energy consumption with 1K       8.53E+06
========================================================</pre>

That's actually less than I thought, by a factor of 100 or 1000 or so, but still ... long.


----
<sub><sup>1</sup> The original primary energy consumption number is from [the IAEA](https://www.iea.org/publications/freepublications/publication/KeyWorld2017.pdf). *Mtoe* stands for *mega ton oil equivalent*, roughly 4,187e+10 J.</sub>