Burgers rock.
I'm sure he didn't literally cutting out burgers only, and nothing else... but...
"1. We would have to try to work out what to do with millions of tons of straw every year"
Shredded Wheat (it's good for your heart)? House Insulation (think Grand Designs on channel 4) ;)
"2. Upland/marginal/river margin land would become unproductive (a sheep can graze on land you cannot get a tractor on)."
Deer parks, nature reserves, or new prisons built in an area no inmate would want to escape to?
"3. You would have to learn to live without other foods, not just burgers. Think milk, cheese, yogurt, cream, bacon etc.."
You are assuming these burgers are 100% beef, which they normally are not, so you can add cheese (I like cheeseburgers), bacon (I like bacon cheese burgers), eggs (to bind the burger together), and milk (sometimes used in light fluffy breads like burger buns, and also milk solids in some burger sauces)... plus, isn't cream, yogurts and cheeses just thick old milk anyway?? :)
"4. If you include Chickens (major methane producer) in the mix, you also loose eggs, and the cheapest and most widely eaten protein source"
MMmmmm... chicken burgers... I love loose chickens, although I think they prefer to be called free range, or "whore" chickens under my roof... but I believe in this case you meant lose?
"5. There would be a serious protein shortage, which would require serious management of the populations diet in the West."
No protein shortages, I think the original suggestion was to just eat less burgers, not cut them out entirely.
"6. The countryside becomes huge expanses of either fallow scrubland (uneconomical to grow crops on), or vast belts of arable monoculture."
Not sure what a vast belt of arable monoculture is, but it sounds itchy and incurable.
"7. Nature abhors a vacuum. Natural animal life (admittedly a lower greenhouse gas producer) will move in where the farmed animals used to be."
Not sure nature dislikes anything, as it's not really a sentient being, but I'm fairly certain a few woodland creatures would have a preferable economic impact than a battery hen factory of thousands.
"8. And finally, if the human population were to move on to a pulse and/or brassica based diet (think brussel sprouts or cabbage for the latter), then WE would probably become the largest producer of methane (at least in my experience!)"
Agreed... I gave my 1 year old a veggie meal yesterday, he's been farting for queen and country all day.
Disclaimer: I have no actual point, I neither agree nor disagree with anything you said - I just picked some random comment and decided a blow by blow comment of my own would fill the time I need to wait for my wife to stop watching america's next top model so I can go bed... sorry if I've wasted anybodies time by wasting my own...