I was shocked - and frankly, really sceptical - to realise that eating meat was one of the biggest climate impacts I was having. On the flip side, that's a good thing, because it's one of the easiest things to change on our own, without upending society. Easier than rerouting the air travel industry! I've been doing it for a couple of years now and hey - it's actually been surprisingly easy and enjoyable.
Yes meat-eating really is an important factor in climate change: see e.g. this recent letter from scientists to the world - but see also the great book "How Bad Are Bananas" for a nice readable intro. For even more detail this 2014 paper and this 2013 paper both quantify the emissions of different diets.
The great thing is you don't have to be totally vegetarian, and you don't have to be an absolutist. Don't set yourself a goal that's way too far out of reach. Don't set yourself up for failure.
So, my climatarian diet. here's how it works:
Actually, that rule is the only rule that I follow as an absolute. Avoid other meat as far as possible, but don't worry too much if you end up having some chicken/pork/etc now and again. The impact of chicken/pork/etc is not to be ignored but it's much less than beef, and I find I've not really wanted much meat since I shifted my eating habits a bit.
I never thought I'd be able to give up on beef (steaks, roasts, burgers) but the weirdest thing is, within a couple of months I just had no inclination towards it. Funny how these seemingly unchangeable things can change.
If CO2 is what you care about then you might end up preferring battery-farmed animals rather than free-range, because if you think about it battery-farming is all about efficiency, and typically uses less resources per animal (it also restricts animal movements) - however, I'm saying this not to justify it but to point out that maybe you don't want to have just a one-track mind.
Vegans have an even better CO2 footprint than vegetarians or almost-ish-vegetarians like me. Vegan food is getting better and better but I don't think I'm going to be ready to set the bar that high for myself, not for the foreseeable. Still, sampling vegan now and again is also worth doing.
Is this plan the ideal one? Of course not. The biggest problem, CO2-wise, is cheese, since personally I just don't know how to cut that out when I'm already cutting out meat etc - it's just a step too far for me. The book "How Bad Are Bananas" points out that a kilogram of cheese often has a CO2 footprint higher than that of some meats. Yet vegetarians who eat cheese still contribute one-third less CO2 than meat-eaters [source], because of course they don't eat a whole cheese steak every day!
You don't have to be perfect - you just have to be a bit better. Give it a go?