A great deal of the modern-day concern about fossil fuel burning can be swept away by imagining a time, roughly six generations from now, when nobody burns carbon out of the ground any more, either because people outlawed the practice or because it's gone. You ask "What happened?"
The premise is science fiction, but it's also a way to separate the technical matters from political ones, which is critically important in this subject. Elementary engineering, physical law and economics so constrain what can happen that you can make reasonable guesses about some things. For example, battery-powered airplanes are probably not in the cards because elementary principles limit a battery's energy-to-weight ratio. That being the case, either there will be no airplanes or people will find a way to make the fuel airplanes need. I will discuss a few similar constraints and their implication for the future.