Which pollutes less: driving a long distance of flying?

It depends on a few factors:

You pollute more if you, drive a car ( all alone) compared to travelling on a fully occupied 747 on a long haul flight.

However, for shorter distances, you are better off in a car. Take off and landing consume a lot of fuel than travel in thin air at 10 km height.

At the height a plane flies, UV light is more and it decomposes a lot of pollutants.

One would argue the plane would take off whether you are on it or not, so from that standpoint you personally aren't creating any CO2 emissions ( although you did drive to the airport right? )

However I suppose most people don't look at it that way. :) Besides, if lots of people decided not to fly the flight would indeed be cancelled.

So...back to your question. It is actually a much more complex problem than you might think. An accurate answer to your question depends on both the car and the plane's CO2 emissions. Also depends on how many people you put the car/plane. If you drive a Hummer by yourself you will get a different number than jamming 5 people into a hybrid sedan. Older planes/cars also have higher emissions than newer ones, etc.

To answer this accurately I would look at the kind of car you plan to drive, find out from the manufacturer how much emissions it puts out, then divide it by the number of people who are going (perhaps making a slight variation for weight). Then do the same for the plane, and you will have your exact comparison.

Based on what I have read if you have a reasonably new car with decent gas mileage it will win most of the time by a decent margin.

In case you care, a train would actually be the most environmentally sound way to travel by a longshot.

Driving. Jets use a lot of fuel--but the engines are a lot more efficient than car engines and so produce less pollution for the number of passengers they carry.