It might be carbon for us, but in general it might just be exponential growth. Exponential growth will always hit some kind of limit in a finite world. e.g. if

It might be carbon for us, but in general it might just be exponential growth. Exponential growth will always hit some kind of limit in a finite world. e.g. if we got a magical free energy source and dealt with carbon emissions, we'd still run into direct issues with waste heat eventually. Even at a seemingly modest 2% yearly growth, energy usage would reach the level of energy Earth receives by the sun in just 500 years or so.