The problem I always see with using taxation to solve problems (to prevent too many people from doing X), is that you're filtering by socioeconomic status. You're making it so that only the richer people can do it, and the poorer people are screwed once again. It's a simple fix from an institutional point of view, and it might "solve" the problem, but it just feels wrong to me. Not that I have a better solution though...

Welcome to the real world. Besides, how many poor people are flying multiple times per year anyway? I don't have the numbers, but I would bet that this tax would be paid overwhelmingly by businesses on behalf of their employees who travel for work.

And that tax would be absorbed unnoticed in the businesses' expense again right next to the reciepts for over-priced steak dinners and strip clubs. The whole reason airlines can get away with charging so much for business class is because businesses don't generally give a shit if their sales personal are charging them for in-flight champagne when they go to close a billion dollar contract. The truth is that you'll have to be more strategic than randomly throwing a tax at the problem if you want to change the behavior of entities who already dump hundreds of thousands on maintaing a private jet fleet so that a C-level doesn't have to wait in line at security.

You could have a revenue-neutral carbon tax, where each person gets a share of the tax proceeds, and then lower income people get paid on net when they don't consume carbon

In the US, we would probably drive our own cars anywhere within a 250 km (150 mi) radius, which costs about $170 in fuel and vehicle maintenance, and takes about 2 hours each way.

Tax flying in the EU, and people will likely take more trains. Try it in the US, and you're just pushing people back into their cars.

For a trip of 150 miles, does flying have a lower carbon footprint than driving? (For that matter, for any distance, same question.)

Airliner aircraft burn more fuel closer to the ground, at takeoff and landing, and less fuel at cruising altitude, where the air resistance is less. On shorter trips, the proportion of the trip spent at lower altitudes is greater. Some flights might not reach optimal cruising altitude at all.

One can adjust the flight profile for maximum fuel efficiency, but this tends to be uncomfortable for the passengers and crew, and it takes longer to reach the destination. Most US passenger airlines don't do that, but military and cargo carriers will.

That aside, some portion of the fuel is spent continuously keeping the weight of the aircraft aloft, and with ground vehicles, the equivalent expenditure is the rolling resistance of the tires. Furthermore, an airliner plane tends to carry all the fuel it needs for the entire flight on takeoff, which translates to additional weight, whereas the ground vehicle can refuel enroute at a truck stop or gas station. Some aircraft can refuel in flight, but another plane has to carry it up there and maneuver it into place. A train on electrified rails need not carry any fuel at all.

So to some extent, it depends on the ground vehicle and the aircraft. In a contest between an ultralight or powered paraglider and a heavy pickup truck towing an RV trailer up in the Rocky Mountains, the flyer might have a lower footprint. But for a trip over flat ground, such as Chicago to Indianapolis or Cincinnati to Cleveland, in a medium-sized hybrid ICE+battery sedan, driving at or below the posted speed limits on US Interstate or Autobahn-like restricted access divided highways, I think the car will win against anything other than a solar-powered lighter-than-air craft.

I haven't done the bar napkin math, so I could be wrong.