I did a quick alalysis and it actually matched the ~1.5 degree celcius rise pretty accurately. It required a bunch of incorrect simplifying assumptions, but it was still interesting how close it comes.

Estimated energy production from all combustion and nuclear from the industrial revolution onwards, assumed that heat was dumped into the atmosphere evenly at once, calculate temperature rise based on atmosphere makeup. Ignores the impact of some of that heat getting sinked into the ground and ocean, and the increased thermal radiation out to space over that period. In general, heat flows from the ground and ocean into the atmosphere instead of the other way around, and the rise in thermal radiation isn't that large.

On the other hand, this isn't something that the smart professionals ever talk about when discussing climate change, so I'm sure that the napkin math working out so close to explaining the whole effect has to be missing something.