I think you will find that flying is, excluding solar power, the most efficient form of transport.
The fuel consumed to move 300 people across the atlantic by 767 is much less than a boat or equivilent distance by car. Of course the number of people on the airplane would affect this but then they carry less fuel due less weight.
And then point out the number of cars occupied by a single person in the M25 or your local stretch of traffic jam, all with the engines running and big engines at that and aircraft pale into insignificance!!
And then when they say, ahh, the electric car, you can counter with, "and where does the electricty come from to charge the batteries?" and when they say about fossil fueled power stations, suggest Nuclear, they are clean and have minimal pollution except when it goes wrong. How many times have there been major accidents over the whole time they have been producing commercial electricty?
Last year in Australia was highlighted because per capita it produces more gas pollution than any other developed country, the simple reason is that Australia only has a population of around 20 million, and the amount of smelting and conversion form raw to refined materials that occurs, per capita it isnt so good.
remember there are Statistics, damn statistics and Lies, back it up with good arguments and youcan get most of the greenies to back down.
Enjoy, Hay Ewe