Weird thing to say to a comment that explicitly says this is about warming the oceans. The original calculation, assuming all the energy is dumped directly into the ocean would be: 87B / (60*60*24*365*4) = 689.69 years.

Funny thing about the atmosphere though is that it requires ~1300x less energy to heat up by 1 degree, so if you dump all that energy into the atmosphere, the temperature would go up by ~2 degrees per year.

The reality is that global warming warms up both the oceans and the atmosphere to varying degrees (and the earth's crust, to much lesser degree), with the ocean absorbing most of that. The atmosphere only absorbs about 23% of that, and a significant amount of the of the excesses radiate back into space.

But even with a conservative estimate that only 1% of this heat is being stored in the atmosphere, that would still lead to a global atmospheric temperature increase of 1 degree Celsius every 50 years. The worst-case scenarios estimate 2% of this heat is retained, dropping that down to 25 years.

I'm going to go ahead and guess that waiting 2.5M years isn't the answer. That's geological time scales anyway, Humans could have gone extinct and been replaced with new intelligent life in that kind of time. Whatever math you did to reach that figure, it's completely wrong.