Viable non-fossil replacement for jet fuel: synthetic kerosene made from various biological sources. Approved for 50% blend on commercial aircraft, some older things depend on fossil components but a very fixable problem if it came to it.

https://aviationbenefits.org/environmental-efficiency/climat...

These guys claim an estimate of $3-4 per gallon (pre-tax and pre-distribution) for synthetic gasoline. Not 20 or $50 per gallon. https://carbonengineering.com/air-to-fuels/

> "Somewhat more expensive" fertilizer means more expensive food, which means starving people, which is horrible on its own, but which could also create a very dangerous political situation.

It really is only somewhat more expensive. Because of natural gas nonsense, the price of nitrogen fertilizer tripled ( https://www.dtnpf.com/agriculture/web/ag/crops/article/2022/... ) and is still getting used, we're talking about a moderate increase in price to switch from methane hydrogen in the amonia-from-air process to electrolyzed water sourced hydrogen.

Lots of nonsense based fearmongering goes around, the actual solutions are sure to exist and don't involve doomsday, but moderate price increases (and probably once they scale, price reductions)