So I have this (possibly dumb) question about the implications of the second law of thermodynamics to the use of renewable energy for the world, so please bear with me. Here goes: Apart from the finiteness of fossil fuels (FFs), which is obviously an issue, the main problem for sustainability in burning FFs for energy is that it leads to the release of greenhouse gases. These trap a lot more of the incoming solar energy than otherwise would have been the case, leading to global warming. OK. So we need to move to solar, wind, nuclear, etc.
But the second law implies that we can only extract some finite amount of energy for useful work, and the rest invariably goes to heat (right?). Solar panels, batteries, wind farms, etc. all presumably leak all unconverted energy into heat. And a lot of this energy is coming from 'outside' the biosphere. So doesn't that mean that even with renewable sources, we will inevitably leak heat into the biosphere leading to at least some global warming?
So isn't it really only a difference of scale in terms of the warming that is caused by greenhouse gases from FFs vs. from renewables? Won't we always heat up the surface, no matter how efficient we get?
Also, increasing efficiency could (and I think tends to) lead scaling up our use of energy, so that the total waste heat generated might still increase. Is it possible to keep the biosphere at the same approximate temperature even if billions more people start using the same amount of energy per capita as say a modern wealthy European does?
So finally, are there 'sinks' for all this excess heat that we could tap into? Space is at ~4 K, right? So can we use space as an infinite heat sink?