On the topic of planes' emissions, does anyone have links handy to studies of the net effects of air travel. It is my impression that short term they may not have a great effect because of the cooling from particulates etc. But long term, iirc, they may have outsize effects even for their outsize emissions per mile since they put ghgs (not just CO2, but also water vapor) at levels of the atmosphere where those gasses are relatively rare, so the percentage increase is far greater than if the emissions were closer to ground level. That's what I recall, anyway; but I can't recall where I recall it from. 
Any help for this aging, feeble mind would be more than welcome.
I think the main issue with planes ultimately is just the way in which they empower individuals to very rapidly dump literally tonnes of carbon dioxide into the atmosphere? The tonnes emitted with planes mount up awfully fast. Some people will point out that the emissions per passenger mile aren't really that unfavourable compared to some cars (especially American ones!) - but that ignores the issue that most people don't take their car and drive thousands of miles a day at the speeds of a modern jet liner (and that cars are still a very serious source of carbon dioxide).
In my case, having operated a very fuel efficient car for only a few years (and no car the rest of the time) and having lived pretty frugally - my modest number of plane trips really hits my lifetime carbon footprint. In fact it's almost certain the tons of jet fuel I've burned are a multiple of the tons of road fuel, given most of those flights were long haul.
Flights are also unfairly cheap compared to other forms of transport because the airlines seem to get special tax breaks on the fuel they burn (at least in the UK). So for road fuel in the UK - you pay approximately $6-9/gallon (for example, but it is really that expensive). Do you suppose the airlines pay that? Certainly not.
So why should a person too poor to fly be paying far more for their fuel to commute to work and put food on their table than a person who is flying thousands of miles for a business meeting that could be done by telephone or for a fancy vacation? That said, maybe the increasingly considerably taxes levied on flying go some way to closing the gap - those aren't directly comparable (though I should note the cost of motoring in the UK is also extremely high, fuel is far from the only major expense incurred).
Flying makes a mockery of the very minor steps most people take to save energy. Buy energy efficient light bulbs, switch off your electronics, buy a fuel efficient car, insulate your house - then throw away all those savings and more with a single plane flight?
