I think people are underestimating the amount of energy production required for sustainability. We use fossil fuels in many other applications besides turning into combustion fuels and if we want to start scrubbing CO2 so we don't turn into Venus that is even more energy. Take fertilizer production for example, we already know it is an energy intensive proccess, a large portion of global energy supply is used on making fertilizer, but it goes farther than that. The base reagents we turn into solid or liquid synthetic fertilizer is more fossil fuels which doesn't get accounted for as energy production, yet it is containing a ton of energy still. We could draw what we need for the fertilizer from the atmosphere and water, but it will increase our energy expenditures for production an entire order of magnitude higher, if not more. Who is counting the carbon pollution from that fertilizer after it comes out of my ass or rots on the ground? The same goes with other processes and materials. Plastics is a big one, nobody counts the amount of 'energy' stored within plastic as a material, plastic doesn't easily degrade, but it does degrade and release its decomposition products into the earth and atmosphere, and at increasing rates if we take the reports of plastic-consuming bacteria evolving and gaining numbers seriously.