Let me lay this out for you. There IS a huge change in climate coming. It WILL affect a lot of food supplies and lives. And those people who have a garden ARE going to be better off. It's that simple. Furthermore, those that are gardening without the use of chemicals (i.e. the permaculturers) will be better off again because they won't be at the mercy of fertiliser and pesticide supply & demand.
So I'm not just disappointed by Ian's gloom and doom outlook. I'm totally disappointed.
I'm not permaculturing my vege patches because I think it'll magically reverse global warming if enough people all follow me and do the same. I'm doing it because I know that it will reduce one person's carbon footprint by a little, it'll make me more aware of the issues involved, it may help slow down the coming disaster, and it will give me a food source that isn't dependent on some supermarket chain and all the trucks and ships that they need to bring me my crisp Romaine lettuce that was grown in the US somewhere and shipped here.
Factory farms (the farms that grow hundreds of acres of one particular crop only, for sale to one particular supermarket or food distribution chain) are an example of why permaculture is better: They grow one crop (for argument's sake let's stick with Romaine lettuce) and that's it. If the six month season is bad for Cos lettuces, then an entire crop might get ploughed back into the ground due to being not quite perfect enough for the market.
The typical factory farm has fields levelled by laser, plants their Cos lettuce seeds with a large machine that chomps through rather a lot of fuel, and then waters it with "side dressings" of fertilisers and growth stimulants, sprays the crop with pesticides targeting the most common Romaine robbing bugs, and ships lettuce from one or two geographical locations to the distribution center from where you'd be surprised where those footloose lettuces end up, sometimes half the world away...
If there's a climate shift or bad few years, that's pretty much it for the Cos lettuce supply around the world.
Permaculture, with its requirement to have redundant solutions for every system, would firstly have other crops in rotation/complement so if their lettuces fail, they are still growing other produce. Furthermore, because it's a lot of small gardens and farms spread over a wide area, there's a chance that the Romaine at your neighbour's place grew up nice and green so you won't miss out. Because the crops are planted and grown using minimal mechanical interference, there's not so much pollution associated with it. Because there is no need to add fertilisers or pesticides, less pollution there, too.
I noticed with amusement that Ian has a sheep dog. Which I'm willing to bet isn't fed on the chickens and sheep that he grows, so that dog food has to come from offsite. And there's really no justification for a dog on a permaculture farm, almost everything (including animal management) should be designed to be low impact, and have redundant systems as well.
Also, there's the problem (illustrated by this charming story here) of prior land use. I noticed that there was a lot of flat ground, which is indicative of the land having been a broadacres farm in a past life. Just as the White House grounds are polluted by lead sludge used as a fertiliser in the past, broadacres land is likely to be contaminated by pesticides and herbicides and fertilisers, and compacted, to boot.
Not having a go at Ian, just pointing out that he's making a difference in the land, improving it from its previous state, and EVERY improvement is cumulative, EVERY person who takes up such an activity makes a few pounds' worth of carbon of difference. I think he should realise that no one person is going to turn the tide, and no one effort (be it recycling, permaculture, slow food, frugality, or whatever) is going to make a huge impact. However, every person growing beans and corn in their back yard is also doing one other very important thing - they are acknowledging that a problem exists, and that will permeate every other facet of their lives...