Air pollution/climate change/etc.
That issue is going to get tougher as our technological needs increase. Got stuff that’s powered? Don’t want to use a foot pedal? Then you need an engine to do it for you. How do you get the engine to do it for you? Electricity is nice. Alternative current back and forth – great for motors.
But then, how do you make electricity? You need a generator. How do you get the generator to generate the electricity? It’s gotta move.
Steam’s nice for that.
How do you make steam?
Water and heat.
How do you get the heat?
and… that’s where things get messy.
But, I don’t see an increase in the demands of foot powdered phone chargers, so I guess “less offensive” noxious burning residue is best. I read something about the debate between shale vs coal; whole things’s a mess.