Getting causal impotence right

Parker’s broad view is that, because metered-dose inhalers (MDIs) emit far more greenhouse gases (GHG) than do dry powder inhalers (DPIs), and the two are equally effective for most patients, the healthcare system should switch most patients on MDIs to DPIs, and the patients have a pro tanto duty to accept this change.1 The problem is that no individual inhaler use causes harmful climate change, and so it is difficult to explain a duty not to use MDIs. It seems that my individual behaviour ‘makes no difference’ to climate change, so familiar more principles have a difficult time justifying a prohibition of such behaviour.

Parker’s response to this worry fits into the consequentialist tradition,2 3 as he argues that each individual contribution to climate change causes some amount of ‘expected harm,’ because it contributes a little bit to future climate changes which will cause harm. And since we have a duty to minimise expected harm, we have a duty not to make such small contributions to climate change.

I think we should be sceptical of this sort of argument. It makes the most sense if we endorse a bathtub metaphor, in which the atmosphere is like a bathtub, and once it is full, every …