I mean, doesn’t the atmosphere in our big greenhouse always retains a non-zero amount of energy, no matter the CO2 etc. in the air? If that is true, then so far the net energy out flux was positive, but now we see with rising greenhouse concentrations that it’s turning. If we then raise the stock of energy inside the greenhouse, it overheats, no?
In any case this stuff will never produce so much as one solitary kWh of commercial power, so the question is wholly academic. Fusion heat would cost much, much more to extract in usable form than fission, and fission is already not competitive.
The dream of unlimited power without spending on fuel -- capex but no opex -- is already here, and we call it renewables + storage. We just need to build it out fast enough that civilization doesn't collapse first. Fusion is a pernicious distraction, in present circumstance.
This is inaccurate, both production and storage have service lives (in years, cycles or both) so need to be continually replaced. This is opex in practice
We currently generate most of this power in exactly the same way, but by burning coal and gas to make heat rather than by nuclear fusion.
The difference would be that no CO2 is released with a fusion power plant.
5W/m^2 or 0.5% is enough forcing to be catastrophic which puts us roughly in the 20x current consumption or 2100-2140 range if we don't stop growth.
So yes. We're in exactly the same position now WRT heat as we were when scientists first started warning about greenhouse gases. Ironically switching to PVs and starting the transition was an option then too even though the first commercial PVs were thought to be thermoelectric.
We can all live well, but we can't all live in an air conditioned uninsulated mcmansion with a 9 tonne electric suv each going everywhere via highway and throwing out half our appliances which we move by truck every year.
10 billion or so people can live at current average western levels without it being a problem.