....Seriously, I think hobbies, whatever they be, will be tailored to fit the cloth. I commented elsewhere that road traffic seemed waaay down on what you'd usually expect for a sunny summer weekend. Loads of people can't afford to drive as much. And haven't birders admitted to swapping long-distance twitching for local patch/county twitching in the past because of expense? Costs will always make us adjust our carbon footprints more than right-on views..
I think you're right Kev. When I look back at my birding career, it's changed from dude, to twitcher, to local patch birder to, to surveyor, to recorder, back to dude again, and now semi local twitcher / biking birder. None of this was planned, it just happened so that I could fit birding in with the rest of my life, (e.g. got job, got married, bought house, had kids, changed jobs, kids growing up etc.). My birding had to adapt or die. Like most other people, no part of my life has ever stayed the same from one year to the next, so my birding has had to evolve to suit. The main changes in my life so far have been driven by time and money, and I don't really see that changing.
To answer the original question, whilst I firmly believe that Global Warming is real and is Man made, and I do many miles by bike, and I recycle all I can, I have no intention of giving up my car or birding holidays abroad, in order to reduce my carbon footprint. It is time and cost that would stop me using the car for birding, twitching or otherwise, not carbon footprints. And prices would have to rise an awful lot more than they are now to stop me flying for example. I enjoy my holidays too much to worry about an extra £100 on the cost.
Incidently, when I last changed jobs, I was out of work for 5 months whilst I looked for a job close to home. I was determined not to travel far to work, and turned down jobs while I was looking. In the end I've ended up 5 miles from home, with no traffic to speak of. Takes me 15 minutes to get to work. It was a difficult 5 months, but now I'm reaping the rewards, and that alone reduces my carbon footprint signifcantly.