I live in the UK, and a question some people here ask is this: why should we bother about emissions in our small country when any small change on our part will be as nothing next to the impact of China and the US? In my view, this argument is wrong-headed because it ignores the manner in which preferences shift over time.
Consider slavery. At some point, in some "liberal" enclave, some people would have started thinking that slavery was morally wrong. At that point, a nay-sayer could reasonably have pointed out that all the total amount of slave-owning in the room was tiny compared with the vast mass of slave-owning in the Deep South, say. Yet it should be clear in retrospect that the efforts of an initial minority to argue a morally correct case can pay off, as more and more people start to listen and see their own values change. (It seems to me that such changes can be seen as propagating through a network, and can be highly non-linear, such that after a slow start things can really gather pace.)
Moving back to the present, when we in Britain see some European countries recycling and controlling their output of rubbish more effectively than we do, and when we see Germany's sustainable energy use at 12% and rising, it affects our political debate. Equally, when policy experts elsewhere look at our rapid adoption of leading standards for sustainable fishery (MSC) and forestry (FSC), they can see that it is possible to make these issues important to consumers.
These effects are certainly going to be subtle at first, but nonetheless very real. It's just much more powerful to be able to point to a policy choice that is already in place elsewhere, rather than an abstract idea which has not been tried. In addition, technologies or standards which are already working elsewhere are relatively easy to import. We hear this argument all the time in the context of the diffusion of technology, but I think it's just as applicable to ideas.
It therefore makes sense for a small country (or individual) to "go green" on three counts. First, the reduction in impacts, however small, is a good in and of itself. Second, there is a political and moral “ripple effect” which can be a potent source of change, both within and between countries. Third, the push to develop new technologies, standards, accounting practices in one place give late movers elsewhere working tools which can then be rapidly adopted.