Will Wilkinson asks whether it's useful to refrain flying in order to prevent global warming. Answer: no. Any one consumer's demand will not impact the level of carbon emitted, just as no consumer who refrains from eating meat will actually cause the amount of meat consumed to fall; the random mismatch in the supply and demand in your local market for chicken will far exceed the number of chickens you might have eaten for any time frame you choose.
So why do it? To create a cultural norm about carbon emissions, or chicken eating, says Will. I have a different intuition, which is that if you want everyone to do something, you are morally bound to do it whether or not they follow suit. I am rethinking that--but I have a sense that those sorts of illogical bourgeois committments to virtue are precisely what allow us to overcome collective action problems without coercion.