As it happens I've advanced the bathtub analogy on AB several times myself, so I was wondering if you'd remembered it coming from me. Although it's probably not original, and works very well. Even the natural variation bit can be accommodated with not much work at all -- the point being that the human contribution is a consistent, and growing, addition to annual carbon emissions, coupled with a consistent, and growing, destruction of "carbon sinks". The natural variations average out, for the most part (and when they do not, that's what causes natural climate change), so you are left with a strong, consistent, and at this point pretty undeniable signal of increased CO2 levels driven heavily by human activity (to say nothing of the artificial greenhouse gases that have no natural variations because they are never produced naturally, although CO2 is the most prolific).
If you're thinking in terms of the UK, there's little we can do ourselves to deal with the problem, it's true. It will take a global effort, and the will is not there. In part, that's because even nations that have historically tried to do something seem to be giving up. In part too, perhaps, it's because there is no way to solve the problem that doesn't also involve such a radical overhaul of how we live that it's hard to imagine anyone agreeing to it.
All the same, 0.08% (or 2% if you neglect the natural CO2) can have a surprisingly large impact when it's 0.08% of such a large number. 2013 human-sourced CO2 emissions were in the order of 35 billion tonnes, so that 2% of that is still a hefty 350 megatonnes. It might well be that if we stopped producing greenhouse gases tomorrow then it would only take six months or so for Chinese output to make up the difference, but then the effects are cumulative anyway so it is still important to at least try and reduce the amount we pump out ourselves.