This topic worries me. As I mentored a young lady flying her dad's 180HP PA-18 a few years back, I reminded her to enjoy it, 'cause one way or another, when she's my age, we just won't be burning 35 liters per hours of leaded Avgas to fly 90 MPH for fun - society just won't find that to be environmentally acceptable, and something is going to change. For my own piloting life since 1975, I look back, and think of the gasoline and jet fuel I have burned. I figure it's around 350,000 liters since 1975, 75% recreational/personal transport, and 25% "work". But that's a lot of pollution I've put out there. Doing that made me a very experienced pilot, and I got some work done, which someone wanted accomplished, but has it benefited society in proportion to the pollution I've put out there? I'm not so sure....
I can, and am, cutting back on flying, no more 200 liter weekend adventures in the plane, just some short flights, and business travel, combined with some recurrent practice on handling and emergencies. I keep my skills up, but don't just go out and burn fuel for no purpose any more. What worries me is how the industry need for light aircraft experienced entry level airline pilots will be met. It takes a lot of gasoline for a pilot to build the amount of solo flying experience we would like to see, to be confident in each pilot before the occupy right seat in a regional airliner. Yes, simulators will be very beneficial in taking on lots of the training needs with zero emission, but I opine that a pilot only gets to be truly "experienced" by venturing out solo a number of times, and scaring the heck out of themselves a few times, so they realize the importance of good decision making. Sure, we can send out four new pilots in a four place GA airplane, so they can learn together, but we hear from time to time about a poor decision resulting in four fatalities, and the need for true "solo" flight is really not met with four pilots collaborating on a decision/mistake .
But the notion of amassing a near thousand hours of solo GA piloting prior to that first right seat job (the norm, when I learned to fly) will be a self solving problem, as most aspiring pilots will simply be unable to afford it! These factors are going to combine to cause significant changes in commercial aviation. The industry will have to accept much less experienced entry level pilots, and compensate for much less "solo" experience to satisfy the demand for safety. Training can do it, but it's got to be different.
I think about my carbon footprint in life. I consciously consider if I can buy local products to reduce needless worldwide shipping. My most glaring and embarrassing error in this regard was my choice to buy the better part of a ton of "Product of Canada" hardwood floor for my house. I found out to my horror upon receipt of the last part of the shipment (which was late), that the wood grown a few Canadian provinces away from me, which could have been finished locally, was in fact sent as raw planks to China by sea, where it was finished and sent back to Canada for sale. That near ton of wood has crossed the pacific ocean twice, and not employed my fellow Canadians in a wood finishing mill! I'm paying a lot more attention to these things now, and only accept offshore products when there is no local equivalent, and, I actually need them.
Whatever happens, the 43 cents per gallon (10 cents per liter) lead free 80/87 I began building piloting experience on, is now at least 190 cents per liter (locally to me) leaded Avgas. I see that most new pilot cannot afford large amounts of this, money or environment. Aviation still a very small fraction of worldwide use, but it's going to become more publicly visible as time goes by, this will not go back into the shadows. We in aviation must apply our experience, and think proactively about reducing are carbon footprint wherever we can...