How much time is enough time to create a technology that will:
allow us to travel at the speed of light
create personal supplies of food and water that follow us around so no one will ever starve
stop any virus like Covid before it starts
prevent any asteroid from ever hitting the Earth
deflect gamma rays from distant supernovas
I want all of the above now so the government should tell big companies to make it so.
The point is that 30 years won't be enough simply because we wish it to be. We can absolutely stop using fossil fuel five minutes from now. We went thousands upon thousands of years without using it. If we stop in 5 minutes the results would not be pretty but humanity would survive in some form. Those advocating 30 years instead of 5 minutes are either stupid, advocating it simply as a method of exerting/gaining control and/or using the rules to tilt economics to allow profiteering in their own favor. 30 years has no more basis in reality than 5 minutes does. This game is as old as the hills. Only the subject matter has changed.
The best alternatives are:
Allow people the freedom to develop technologies as they see fit. If green energy is where they choose to be then fine. Government should aggressively combat any monopolistic behavior to designed prevent development.
Along with the above, truly assess and measure the impacts of fossil fuel use from all angles, including how many will die without it. We clearly don't have the technology or the will to be 100% accurate in that regard but give it a shot. This way we will be as informed as possible.
Wishing for a solar powered 747 in 30 years is preposterous and the politicians currently pushing it are the same ones who want to eliminate the rich. How will that work exactly? Will some middle class dude in his garage tinker around with solar jet engines until they are perfected and hand them over to AOC so she can save the world?