I know that facts and figures aren't everything, but if we're going to think about why flying is such a big issue, we need to put it in some kind of context. I do believe that flying is the elephant in the room when it comes to cutting our carbon emissions, and it's a very big elephant.
The average citizen of the UK is responsible for about 11 tonnes of carbon dioxide emissions per year. The world average is about 4 tonnes. We all need to reduce our emissions to 1-2 tonnes a year if we're going to give the planet a better-than-even chance of sustaining human life. In my family I reckon we're down to about 4-5 tonnes a person so far - including one tonne per person for travel, one for domestic energy use, one for food and one for everything else we buy.
The trouble with flying is that it blows these efforts completely out of the water. Now, don't be fooled by the figures some airlines etc may quote for the carbon emissions of flying, which may refer literally to the amount of carbon dioxide created when the aircraft's engines burn kerosene (fuel). The trouble is that the plane's effect on global warming comes mainly from other sources, mostly the effect of the water vapour that those engines also produce, and the fact that they produce it at high altitudes. There's some debate about exactly how damaging these other emissions are, but the consensus seems to be that you need to triple the figure for carbon dioxide alone, to get a reasonable idea of the plane's overall contribution to climate change.
This means that the contribution I make to climate change if I fly to, say, Italy and back, is equivalent to about 1.5 tonnes of carbon dioxide - more than my "travel" budget for the entire year. If I fly to New York, it's over 4 tonnes. Australia, 11 tonnes. So, if we succeed in getting our personal carbon footprints down to the kind of level the Government has signed us up to - say 2 tonnes each - that flight to Australia will cost you 5 years of doing absolutely nothing - no eating, no heating, no car, no nothing. Even the flight to the USA will cost you 2 years of total abstention. And yes, the industry is working to reduce its footprint, with bigger planes, straighter flight paths and less stacking, but those are only going to deliver marginal savings, they don't change the game.
So I think it's clear that aviation has no place in our future. It's simply impossible to achieve the kind of carbon reductions we need to make, while flying anywhere.
That leaves us all with the question of how quickly we're willing to make the transition to not flying. Some of us might say "Lord let me be chaste, but not yet". Others of us might argue that we can't suddenly stop flying because we arrive here with circumstances we can't immediately change, like close family in foreign countries that we want to visit. And that's a tough one. My own family moved en masse to the west of Ireland, and I've decided that from now on I'll visit them by car and ferry, or bus, or train. If they'd moved to the USA, I'm not sure what I'd decide. (In fact, previous generations of my family did move to the USA, including my own parents until just before I was born, and people generally just accepted that they'd see each other very rarely, if ever again.)
I don't want to make any absolute judgements about whether other people should ever fly. I've decided that I won't, but I understand that people might feel a need to fly to visit distant relatives (occasionally!), or for certain kinds of work that might possibly be worth the environmental cost. But I do think we owe it to each other, to the planet and especially as Jane says to the planet's poorest people, to think very long and hard before we buy a plane ticket.