Its a bit of linguistic pedantry: https://www.merriam-webster.com/words-at-play/fewer-vs-less

Except they didn't even correct correctly. GP said "We need to find ways for people to burn less carbon," which is totally correct. "Carbon" is being used as a mass noun.

I don't know if you are referring about my comment "fewer hydrocarbons", but it was a direct reference to the post I was referring to, "cool way to burn hydrocarbons". I wasn't trying to be pedantic or correcting anybody. Maybe I should have said less, but... I just didn't. The point is simply that higher efficiency doesn't directly equate to more usage; though it can in some cases.

My bad, I misinterpreted the intent behind the emphasis. Sorry :)

That rule only exists for prescriptive wannabe grammarians anyway.

Generally these planes fly very high and encounter reduced air resistance.

Okay, but 9 Mach is a lot. And flying higher also burns more fuel to reach that altitude. Not sure which of the effects dominate though.

All in all, I'd be extremely surprised if this technology reduces fuel consumption.

The only mention in the text about fuel usage is that they need to use a special engine with lower fuel consumption to even be able to put people and equipment on the plane. Why don't regular jets have that problem? Because they don't consume that much fuel.