I'm sorry, but this argument seems rather confused to me.
Assuming some upper limit on the cost you're willing to pay to reduce carbon emissions, your best strategy is to choose the option that provides the greatest reduction for the least personal cost.
No, it's to choose the best n options, up to the point at which you reach your cost limit. Depending on the limit, and the options you face, n could be 0, or 20, or 100; but there's no particular reason to think it should be 1.
Of course, assuming a fixed upper bound on willingness to sacrifice runs counter to the idea that the sacrifices you're willing to bear should depend on the benefits obtained. There are two alternative perspectives you could take here:
From the perspective of what's best for human welfare generally (which was the basis of my original claim) you simply shouldn't have such a limit. If the net effect of an option (taking into account opportunity costs) is positive, you should just do it (This applies even if the option is suicide, though the opportunity cost of suicide is probably quite high compared with other ways of promoting human welfare.)
From the perspective of an imperfect altruist, a better way to think about it is in terms of the marginal rate of substitution that you're willing to accept between your own welfare and others'. This will presumably increase as your own welfare decreases (and is probably the real reason we wouldn't commit suicide to reduce emissions, even if the benefits to others did outweigh the personal and opportunity costs).
You've got to consider opportunity cost and marginal utility.
Agreed. The thing is, the opportunity cost of becoming vegetarian isn't like the opportunity cost of $5. If I spend $5 on carbon offsets, that's $5 I can't spend on something else. If I become vegetarian, I haven't really used up a resource that I could have done something else with; in fact I've probably saved money (maybe I've used up a bit of willpower in the process, I'm gonna say the effect is minimal). The opportunity cost of vegetarianism is my direct loss of utility minus whatever utility I can get from the money I've saved.
Assuming the costs can simply be summed
They can be, if you denominate them in human welfare. They clearly can't if you denominate them in dollars, but I never claimed they could be, and my argument doesn't rest on it.
it needs to reduce emissions more effectively than other equally costly options.
Perhaps I'm misunderstanding, but this still seems inaccurate to me. If there is a more effective yet equally costly option O, but the total benefit of O+Vegetarian is still greater than the total cost of O+Vegetarian, then Vegetarian is still worth it (as is O). Your framing seems to deny this.
My original question was an attempt to ascertain whether the reduction in greenhouse gas emissions was truly your primary reason for choosing vegetarianism
Yes. It was, and is. I guess there's an added benefit in terms of cost, but given that I don't care about the animals themselves, I really don't have any other reasons for it.
The (seemingly) more common animal welfare justification for vegetarianism seems more directly linked to the particular decision to not eat meat than does a carbon emissions argument.
Sure. But it would hard to get a more direct link than the animal welfare argument, so that's not saying much. Something in the order of 20% of global GHG emissions can be attributed to livestock, so it's not like the link between meat and emissions is weak.
I guess the complication is that there's a reasonable amount of variation in emissions depending on what meat you're talking about. Ruminants (cows, sheep) are especially bad (because of the methane), as is dairy (for the same reason). Farmed and deep sea fish are pretty bad too, but other fish are probably OK. Chicken (and especially eggs) aren't so bad either (and are probably better the worse you treat the chickens).
Ultimately, I figured that it would be easier (and therefore more effective) to have a clear no meat rule than to try to make too many case-by-case calls that I might then be tempted to weasel out of. Nonetheless, in an effort to become slightly more consistent, I've made a deal with myself that I can start eating (OK) fish again if/when I manage to completely ditch the dairy (given that the latter is almost certainly worse from a GHG perspective). Haven't quite managed it yet though.
It's not clear to me that vegetarianism would be the best choice
Given that vegetarianism doesn't exclude other strategies for emissions reduction, I'm unclear why you think it's relevant whether or not it's the single best strategy. Surely all that's required is that it have a net positive effect?
it seems like it would be a bit too convenient if a comprehensive cost benefit analysis came out with the answer 'become a vegetarian'
Convenient for people who are vegetarians on other grounds, perhaps; not so much for me.
In any event, I don't think anyone was suggesting that vegetarianism is the single best way to reduce your carbon footprint. (The specific suggestion being made was presumably that becoming vegetarian was likely to be more effective than buying an equivalent tonnage of offsets. I think this was true when I became vegetarian, but perhaps the certification mechanisms for offsets have now improved enough that the real issue is cost.)
Whether vegetarianism could be the single best way for any given individual to reduce their carbon footprint will depend heavily on: (a) what margin you're working at (e.g. if you already don't drive or fly much, but eat a lot of red meat and dairy then it's more likely to have a large percentage impact); and (b) the relative value you place on the activities that you could scale back on (which will also vary from person to person).
To get somewhat more precise, the paper I linked to in my previous comment concludes:
a person consuming a mixed diet with the mean American caloric content and composition causes the emissions of 1485 kg CO2-equivalent above the emissions associated with consuming the same number of calories, but from plant sources. Far from trivial, nationally this difference amounts to over 6% of the total U.S. greenhouse gas emissions.
Individual mileage will vary of course. Because my carbon footprint was already pretty low (around 1/4 to 1/3 of the US average), I estimated the reductions I could achieve by eliminating meat and dairy at somewhere around 20%. (Which pretty much did make it the best single option I had.)
FWIW, I'm a little unsure about the value of buying local for a couple of reasons.
Variation in production efficiency can swamp transport costs. The classic example here is that it's apparently more energy efficient to ship lamb from New Zealand than to produce it in the UK. (Though much of this apparently comes down to coal vs. hydro electricity generation, and won't apply to all forms of production.) More broadly, I worry that increasing demand for local products because they are local could incentivise inefficient production.
Large supermarket chains actually have pretty efficient distribution systems, and, as I understand it, most of the emissions from food transport tend to enter at the point-of-sale to front-door stage anyway.
(Not convinced it's bad, either. Just unsure about the size of the benefits.)
If your main reason for eating a vegetarian diet is to reduce your carbon footprint, how effective is your dietary choice? My impression is "not particularly".
Is that impression based on anything in particular? The evidence that it will reduce one's individual carbon footprint seems fairly solid (see e.g. here) . The extent to which that translates, via reduced demand, into actual emission reductions is perhaps more arguable, but that doesn't seem to be what you're getting at. Conversely, there are rather more serious, and well-recognised concerns about the efficacy of offsets.
he doesn't really miss it any more so he didn't appear to be attempting to persuade anybody.
Actually, I think the fact that it's possible to adapt pretty easily to a meat-free diet strengthens the case for others doing (or at least trying) it.
P.S. What makes you assume I'm male?
Assuming I felt like it, it would depend significantly on the efficiency (particularly energy efficiency) of the production process.
I think that's an accurate characterization of my concerns. I didn't take the offset route for three main reasons.
I think we're pretty much in agreement. Any remaining differences are either trivial, semantic, or (at the risk of angering the Aumann Gods) "things reasonable people can disagree about".