The thermodynamics and energy density is irrelevant. The external costs of fossil fuels in a scenario without a green transition is so enormous that it can lite

The thermodynamics and energy density is irrelevant. The external costs of fossil fuels in a scenario without a green transition is so enormous that it can literally crash the current civilization. That means the net savings could also in the worst case scenario be the entire world economy plus all future growth for thousands or even more years.